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Technical investigation and restoration

The evolution of preparations for painting on canvas in sixteenth century Spain Pantoja de la Cruz, Juan

In the mid-sixteenth century canvas replaced wood as the typical support in Spanish painting. This change brought with it a review of the usual systems of preparing the surfaces before painting. Based on the analysis of microsamples from several works in the Museo del Prado collection, this article traces the evolution of the preparation of canvases in sixteenth- and seventeenth-century Spain. The information obtained is compared with the instructions found in the main treatises of the period.

Boletín del Museo del Prado, Tomo XXVIII n.º 46, pp. 39-59, 2010 (english translation):

The evolution of preparations for painting on canvas in sixteenth and seventeeth century Spain

María Dolores Gayo and Maite Jover de Celis. Analysis lab, Museo Nacional del Prado

The evolution of preparations for painting on canvas in sixteenth century Spain

Margaret of Austria, Juan Pantoja de la Cruz. 1606. Oil on canvas, 207 x 122 cm.

Introduction

The introduction of canvas as a support for painting, brought about by Venetian painters who developed and popularized its use, was a giant step forward in the history of art. Canvas possessed numerous advantages compared to traditional painting supports: it was more resistant to damp than fresco painting, and at the same time it permitted larger formats than wooden panels, it was less costly and less prone to deterioration (cracking, insect damage, etc.) and, as it was lighter and could be rolled up, it was easier to transport1.

In the mid-sixteenth century, following the example of Italy, painting on canvas began to develop in Spain. In Northern Europe, however, the use of panels would continue as the main medium support for easel painting, especially for important works, and it was not until the seventeenth century that the use of canvas would finally prevail2.

This shift towards the use of canvas as a support brought with it a new preparation procedure to prime it before the painting process began, since the system used for panels (applying thick coats of gypsum or calcium carbonate aggregated with animal glue), proved to be too rigid for such a flexible, deformable material as canvas. Thus commenced the search for alternative formulas to attain a surface suited to the new requirements arising from a base layer possessing very different characteristics and behaviour.

That search not only extended to the suitability of the materials in terms of their physical properties –such as flexibility, absorption, and drying– but also to an artistic transition moving towards new lighting and colour effects which would be effected by the colour chosen for the surface to be painted on. The aim was to find a procedure that guarantee proper conservation of the painting while also contributing attractive possibilities as a starting point to create shadows, backgrounds and colours.

The terminology employed to refer to the inner layers of a painting has always been confusing and, in a certain sense, contradictory. In this study we have opted for the following definitions:

  • Preparation: is the modern term used to refer to the whole set of layers which are applied to the support to facilitate painting on it. The preparation comprises both the ground layer and the priming layer. 
  • Ground layer: its role is to isolate the support. It is generally formed by a succession of layers; the innermost one is an organic sizing which acts as a sealant coating usually covered by other layers of inert materials, such as gypsum or calcium carbonate, with the aim of creating a smooth, flat surface3. This succession of layers can be finished off with a final layer of animal glue or of drying oil which reduces the absorption of this porous surface.
  • Priming layer: this layer, which possesses a specific colour freely chosen by the artist, will be in direct contact with the paint. Most often the priming layer is oil-based, something that also helps to seal the ground layer, and in this manner prevents the painting having a matte appearance. It is also possible to paint directly onto a colourless ground layer, though this was infrequent in the period we are referring to and its usage was not been described as a commonplace practice in contemporary treatises4.

In publications, especially in English, it is quite common to find the term «double ground» used to describe this system. However, in this article we have opted to employ the terms explained previously, owing to their more widespread usage in Spanish terminology, particularly in artistic treatises on Baroque painting which we will be referring to further on.

The objective of this paper is, therefore, to initiate a study of the development of preparations for painting on canvas in sixteen and seventeen century Spain. To this end we have compared works by various painters at different moments in time, systematically analysing the colour and composition of the aforesaid layers. Furthermore, we have had recourse to studies of other works published in the literature in the last few years, comparing the results with the painting procedures recorded in the artistic treatises of the period.

In a separate section, we have studied the preparations used by a group of artists who worked together on a single project: the decoration of the Hall of Realms in the new Buen Retiro Palace, from 1634 to 1635. This commission, quite unique in terms of the painting of the period, provides us with a collection of works by Spanish artists in a single setting, and with the opportunity to compare the features of precisely contemporaneous examples.

The existing information we have about the materials employed by the artists is scanty and incomplete. This paper aims to take the first step in researching this broad and complex subject, which is open to review and to development in other directions. The addition of new data from the study of more paintings by the Prado Museum’s Analysis Laboratory combined with data from specialist literature will allow for a more comprehensive study.

1

Despite the obvious advantages of canvas, at first it was regarded as a second-class material, due perhaps to its comparatively low price. Felipe de Guevara expresses his opinion along these lines in Comentario de la Pintura [Comments About Painting], written in about 1560, regarding the quality of the supports made using canvas compared to the traditional wooden panel. While he admits the usefulness of canvases - "they are most convenient [...] by being portable one may more easily move them from one place to another"-, he continues to regard them as a flawed material compared to the "excellence" he ascribes to painting on panel. According to this author "This latest technique of painting with oils on canvas is generally so well-received this day and age, that I almost think it has [sic] acevilado "debased" [a variant spelling of envilecido according to a clarifying note by Antonio Ponz, or acivilado according to the Dictionary of the Real Academia Española de la Lengua] painting to a large extent, having overthrown the authority and perpetuity of panels". One needs to bear in mind, however, that Guevara was not himself a painter, and his comments are therefore those of a theoretician and not of someone who knew his materials and was required to use them in his profession. F. DE GUEVARA, Comentario de la Pintura [...] y algunas notas de Antonio Ponz, Jerónimo Ortega (ed.), Madrid, 1788, p.75.

2

A noteworthy example of this may be found in the many works, including large-scale pieces, painted on panel by Peter Paul Rubens, which coexisted with his use of the canvas right up until his death in 1640.

3

The Spanish term for ground layer, "aparejo", is used in the sense of "parejo", which means even, smooth and uniform, to allude to the characteristics a surface prepared for painting should possess.

4

In effect, it is more common to find paint applied directly on top of the ground layer when it comes to painting on wooden panels. See M. GÓMEZ and M. JOVER "Fernando Gallego en Trujillo: Estudios Químicos", Bienes Culturales, 8 (2008), pp. 49-60, and M. GÓMEZ, "Estudio analítico de la técnica pictórica. Aplicación a tablas y retablos españoles", in A. SERRA et al., La pintura europea sobre tabla. Siglos XV, XVI y XVII, Madrid, 2010, pp. 148-159.

The artistic treatises

Of the various artistic treatises written in this period, the ones by the painters Francisco Pacheco (1564-1644), Vicente Carducho (1576-1638) and Antonio Palomino (1655-1726) contain the most detailed explanations about the materials used5. In all three cases the treatises deal with the art of painting in general and include, at shorter or greater length, references to the materials and the procedures employed by artists. In addition, the text often includes an assessment of methods by comparing technique and approaches.

Arte de la Pintura [The Art of Painting] by Francisco Pacheco, was published posthumously in 1649. The Libro Tercero [Third Volume] is the most interesting from the point of view of artistic techniques and it contains detailed descriptions of procedures to follow in choosing materials and tools, in preparing supports, mixing colours, etc. This artist and theorist not only regarded the canvas as a recommendable support, he went as far as to extol its advantages: «the invention of oil painting on canvas was very useful because of the risk panels have of opening and because of its lightness making it easy to carry paintings to various provinces»5. With regard to the application and composition of the ground layer and
the priming layer, he considers a number of different systems and evaluates the suitability of each6:

"

Some prepare with a porridge made of flour or spelt meal, cooking oil and a little honey (a not very appetizing, almost edible, mixture) […] and once it dries they apply pumice stone to it and prime it with oil

In other words, it is a very organic style ground layer (flour starch, oil, sugars from honey), but without any inert materials which therefore made it prone to deterioration when exposed to a damp atmosphere, something the author also points out. He goes on by describing other methods,

"

Others ground with glove glue, which after drying is applied with the same again, tempered with finely sifted gypsum […] and they prime it with a brush once or twice

This refers to a gypsum and glue ground layer, similar to the ones used to prepare panels, but unlike these it was applied in a single layer.

"

Others ground the canvases with glove glue and finely sifted ash, instead of gypsum and […] they prime it solely with common red ochre ground up with linseed oil; this they use in Madrid

On this occasion, ashes are used to ground the canvas and a red priming layer is applied on top on which to paint, and he expressly associates this technique with painters from Madrid.

"

Others employ a priming layer made of white lead, red lead and charcoal black all ground together with linseed oil on top of a gypsum ground layer

This priming layer produced a warm grey tone, which was also applied on top of a gypsum ground layer.

Those first four methods involve a relatively thick ground layer containing varying amounts of organic material. Pacheco discouraged their use because «the canvases get damp and rot over time and the painted areas scab and flake». He suggests an alternative system:

"

A more reliable means I have found is soft glove glue… which is used thinly to cover the pores of the canvas; leave it to soak in well and […] prime it on top […]. The best and smoothest priming layer is that kind of clay used in Seville, ground to powder and tempered on the millstone with linseed oil […] to which you may add, if you wish, some lead white to the clay to give it more body

In other words, he proposes a ground layer reduced to solely a few hands of animal glue covered by a thick priming layer (he specifies at least threes coats should be applied) made of clay and a touch of lead white which would act as a siccative7. This was the method employed by the painters of Seville.

When it comes to describing materials and methods, The Eighth Dialogue of Vicente Carducho’s Diálogos de la Pintura(1633) [Painting Dialogues] is quite meagre in details compared to Pacheco’s treatise. As regards the process of readying the canvases prior to being painted in oils, his only comment is: «firstly coating with glue that which is to be painted on, and afterwards the rest of the gypsum ground layers and priming layers are added»8. So he mentions animal glue followed by a gypsum ground layer and a priming layer, but without describing in any detail the kind of binder each layer should use nor its amount or thickness. Since our study includes an analysis of various micro-samples taken from works by Vicente Carducho, later on we will discuss the correlation between these instructions and the method actually employed by the author.

Lastly, the volume La práctica de la pintura [The Practice of Painting], from the complete work El Museo Pictórico y Escala Óptica (1715-1724) [The Pictorial Museum and Optical Scale] by Palomino, is extraordinarily prolific in explanations and all kinds of considerations regarding the right or wrong practice of a painter’s trade. It describes, among other matters, materials and utensils, ways to stitch the canvas, its properties, how to nail it in addition to ways to prepare it prior to painting. Like Pacheco, he weighs the many advantages of the use of canvases in comparison to panels, a support he recommends solely for small-scale works which do not entail assembling various pieces. With regard to the preparation of the canvas, he mentions a variety of methods, which generally coincide with the ones described by Pacheco9:

"

The first coat for the ground layer […] is made by heating water […] and then adding finely sifted flour to it […]; some people subsequently add a little honey and a touch of linseed oil according to their liking, but not ordinary cooking oil.

This ground layer, devoid of inorganic inert materials, is the same as the first one described by Pacheco, and Palomino too discourages its use «because it becomes mouldy when left in damp places». He continues: «The other method of preparing the canvas in the first coating is with glove glue». This type of thinner and organic ground layer was the one most recommended by Pacheco and it appears that Palomino prefers it too as he does not mention any drawbacks to its use whatsoever. At the end of the chapter he refers to a final system which in his opinion is not to be recommended: it is the same one made of ashes and animal glue that Pacheco mentioned. Palomino regards these ground layers as excessively thick and rigid, deeming it better for the priming layer to be practically touching the canvas10.

In the next paragraph he goes on to describe oil priming layers, noting the differences between techniques followed in Seville and Madrid. Firstly he describes –generally coinciding with Pacheco– a clay priming layer, made mainly of ferruginous clays and an oil binding:

"

Made for this or that kind of ground layer, an oil-based priming layer is prepared, which in Andalusia and other places is made from river silt deposited during flooding which, when it dries in hollows, can be prised up like shingles.

With regard to Madrid he clarifies

"

… when this is not available, greda may be used, which in Madrid they call tierra de Esquivias, the kind used to cure wine, the priming layer is made, grinding it up firstly on a stone mill […] and then adding a small amount of red ochre to grant it colour and consistency, and mixing in linseed oil.

This priming layer uses a different type of white clay called greda, which is coloured by adding red oxide pigments11. This layer is the same colour as the one described by Pacheco, but has different components, since Pacheco makes no mention of greda.

Lastly, in both cases Palomino advises adding some kind of siccative, «since both silt and greda are non-drying». He is referring to the addition of «a portion of old colours»12 –in other words, the leftovers of colours on the palette or sometimes, the direct use of «sombra del viejo» [umber pigments], associated with very dark brown coloured shading pigments composed of manganese oxides– which actively encourages the drying of oils. Other pigments with siccative properties could be found in palette leftovers (such as white lead, copper and cobalt pigments and manganese too).

Both Carducho and Palomino, mention how incommodious this process of preparing the canvases prior to painting is for artists, a task that should be carried out by «millers, or servants» or entrusted directly to specialist workshops. This detail is worth bearing in mind when it comes to trying to understand some of the similarities between works by different artists or discrepancies in the oeuvre of a single painter who seemingly employs different materials indistinctly.

The extent to which the methodological descriptions contained in these treatises faithfully reflected real practices and whether they have been borne out by current analytical data will be assessed in subsequent sections.

5

F. PACHECO, Arte de la pintura (1649), Bonaventura Bassegoda (ed.), Madrid, 1990, pp. 480-490; V. CARDUCHO, Diálogos de la pintura, imprenta de Manuel Galiano, Madrid, 1865, pp. 296-301; A. PALOMINO, Museo pictórico y escala óptica. Tomo II: La práctica de la pintura (1715), Madrid, 1988, pp. 125-134.

6

PACHECO, op. cit. (note 5), p. 481.

7

Ibid, p. 481.

8

CARDUCHO, op. cit. (note 5), p. 297

9

PACHECO, op. cit. (note 5), p. 481; PALOMINO, op. cit. (note 5), p. 134.

10

Ibid, p. 130. With the term "Tierra de Esquivias" he refers to a greda (a whitish, sandy clay) from this area of Toledo, which was used to cure wines and liquors in much of Castile. This term has been shrouded by a degree of confusion as it has been mistakenly identified on occasions as creta (calcium carbonate). The Diccionario de la Lengua Castellana [Dictionary of the Spanish Language] of 1734, p. 78, 2, defines it as: "A type of sticky, white earth, often used to mill and wash woollen fabrics and cloth, and to clarify wine in addition to other functions". See also VVAA, Semanario de Agricultura y Artes dirigido a los párrocos, Real Jardín Botánico, Madrid, (21) 1798, pp. 362-363 and A. HERRERA, Agricultura General, imprenta de Josef de Urrutia, Madrid, 1790, p. 379.

11

PALOMINO, op. cit. (note 5), p. 134.

12

CARDUCHO, op. cit. (note 5), p. 299: «in Madrid there are professional primers to relieve us of this burden»; en PALOMINO, op. cit. (note 5), p. 134.

Methodology

About 70 Spanish paintings have been included in this study. The paintings, most of which belong to the Prado Museum’s collection, were executed by masters who were, for the most part, active at the Hagsburg court in Madrid. Evidently this collection of paintings is only a small group if we consider it in terms of the entire artistic output of the period; however, the paintings analysed were by artists whose work had an influence on their contemporaries.

Micro-samples taken from the paintings have been used for the purposes of this study. The samples analysed the various preparatory layers, and also recorded the visual observation of their colour and measured the presence of additives blended into the mixes to alter colour or to encourage the drying process13.

13

Analysis techniques employed: an optical microscope with polarized light for observing the colours of the layers and the stain tests; a scanning electron microscope - microanalysis by energy-dispersive X-ray spectroscopy (SEM-EDX) for analysing pigments and inert materials as well as for estimating the proportions of elements present; gas chromatography mass spectrometry (GC-MS) for analysing binding media.

Results: Tradition

(Table 1)

The process of preparing canvases was based on the tradition of preparing panels using thick successive layers of gypsum and animal-based glue, on top of which a thin, and generally light-toned, priming layer could be applied, which sealed the absorbent surface and provided it with a light base on which to build the painting.

The preparation of panels had not changed substantially over the centuries, old methods and materials were still used as is reflected by the art treatises and confirmed by laboratory analysis. Even some seventeenth century works by Fray Juan Bautista Maíno (1581-1649) –Saint Catherine of Siena and Saint Dominic, from the altarpiece of the church of San Pedro Mártir, painted from 1612 to 1614– and by Francisco de Zurbarán (1598-1664) –the works made for the Charterhouse in Jerez, painted in about 1639– are good examples of late paintings on panels employing a traditional gypsum and animal glue ground layer, despite the fact these artists had embraced the new techniques when painting on canvas14.

The most immediate solution adopted by artists using canvases in the midsixteenth century was to reduce the number and thickness of the ground layers, while still employing the same materials: gypsum and animal glue. On top of this first layer, a clear or coloured priming layer could be applied. In Spain, a method of this kind may be found in a number of the works attributed to Alonso Sánchez Coello (1531/32-1588), which retain the use of a gypsum ground layer covered by a thin, light-grey, priming layer15.

In artistic circles in Toledo at the end of the sixteenth century, we know of one studio which continued to use gypsum and animal glue ground layers on canvases: the studio of the painter Blas de Prado (c. 1555-1599), to whom a few surviving works are attributed. In one of these, Holy Family with Saint Ildephonsus of Toledo, John the Baptist and Master Alonso de Villegas (1589), we discovered quite a peculiar priming layer: applied on top of the gypsum and animal glue ground layer there is a priming layer consisting of white lead, finely ground charcoal blackand thick grains of red lead bound together with linseed oil (fig. 1). Despite being exactly one of the types of priming layer described by Pacheco in his treatise16, it has not proved very common in the group of works analysed17.

El Greco is another artist who preserved his customary technique of covering the gypsum ground layer with reddish-toned priming layers (fig. 2), even in works painted well into the seventeenth century18. Possibly due to his Venetian training, from the outset El Greco employed warm priming layers, often attained by a complex mixture of pigments: white lead, red earth pigments, charcoal black, lead tin yellow, red lake and azurite. This wide range of ingredients was not intentional, rather it was the outcome, in all likelihood, of using paint leftovers from his palette, the “old colours” mentioned earlier, which allowed for a more economical use of the materials while at the same time obtaining a suitably toned surface for painting.

In the earliest work we know for certain was painted by this artist in Spain, and from which we have been able to obtain data (The Martyrdom of Saint Maurice and the Theban Legion, 1580–1582), we find a light-toned, reddish priming layer made from a mixture of white lead and earth pigments. In the works from a later period, however, the artist favours a patently reddish or brownish coloured priming layer, with much more intense tones19.

<p><strong>Fig.1(a):&nbsp;</strong>Blas de Prado, <em>Holy Family with Ildephonsus of Toledo,&nbsp;John the Baptist and Master Alonso de Villegas</em>, 1589. 209 x&nbsp;165 cm (P-1059).</p>

Fig.1(a): Blas de Prado, Holy Family with Ildephonsus of Toledo, John the Baptist and Master Alonso de Villegas, 1589. 209 x 165 cm (P-1059).

<p><strong>Fig.1(b):&nbsp;</strong>Blas de Prado, <em>Holy Family with Ildephonsus of Toledo,&nbsp;John the Baptist and Master Alonso de Villegas</em>. This cross-section of the micro-sample&nbsp;shows the gypsum ground layer (<em>aparejo</em>) and the grey&nbsp;priming layer (<em>imprimaci&oacute;n</em>) containing thick agglomerates of&nbsp;red lead.</p>

Fig.1(b): Blas de Prado, Holy Family with Ildephonsus of Toledo, John the Baptist and Master Alonso de Villegas. This cross-section of the micro-sample shows the gypsum ground layer (aparejo) and the grey priming layer (imprimación) containing thick agglomerates of red lead.

<p><strong>Fig.2(a):&nbsp;</strong>Detail of El Greco, <em>Adoration of the shepherds</em>. The brownish tone of the priming&nbsp;layer (imprimaci&oacute;n) is perceptible in the cross-section of the&nbsp;micro-sample, and can be seen especially in the background&nbsp;and the edges of the figure around its back and under its&nbsp;hand.</p>

Fig.2(a): Detail of El Greco, Adoration of the shepherds. The brownish tone of the priming layer (imprimación) is perceptible in the cross-section of the micro-sample, and can be seen especially in the background and the edges of the figure around its back and under its hand.

<p><strong>Fig.2(a): </strong>Detail of El Greco, Adoration of the shepherds, 1612-14.&nbsp;319 x 180 cm (P-2988).</p>

Fig.2(a): Detail of El Greco, Adoration of the shepherds, 1612-14. 319 x 180 cm (P-2988).

<p><strong>Table 1.</strong> Datos obtenidos en el Laboratorio de An&aacute;lisis del &Aacute;rea de Restauraci&oacute;n del Museo Nacional del Prado. De no especificarse lo contrario, las obras pertenecen a la colecci&oacute;n de dicho Museo. Se incluye, adem&aacute;s, informaci&oacute;n complementaria que se identifica en las tablas con el siguiente c&oacute;digo: (a) informaci&oacute;n extra&iacute;da de la bibliograf&iacute;a; (b) datos proporcionados por Patrimonio Nacional; (c) datos facilitados por el Instituto del Patrimonio Cultural de Espa&ntilde;a (IPCE). Se indica en negrita el pigmento o material de carga mayoritario en las capas de imprimaci&oacute;n y de aparejo con composici&oacute;n heterog&eacute;nea.</p>

Table 1. Datos obtenidos en el Laboratorio de Análisis del Área de Restauración del Museo Nacional del Prado. De no especificarse lo contrario, las obras pertenecen a la colección de dicho Museo. Se incluye, además, información complementaria que se identifica en las tablas con el siguiente código: (a) información extraída de la bibliografía; (b) datos proporcionados por Patrimonio Nacional; (c) datos facilitados por el Instituto del Patrimonio Cultural de España (IPCE). Se indica en negrita el pigmento o material de carga mayoritario en las capas de imprimación y de aparejo con composición heterogénea.

14

See M. D. GAYO, «Materiales y apuntes sobre la técnica de ejecución utilizados por Francisco Zurbarán en la serie de pinturas de la cartuja de Jerez» in J. A. BUCES AGUADO (coord.), Estudio y Conservación de los Monjes de la Cartuja de Jerez, Madrid, 1998, pp. 117-135; Z. VÉLIZ, «Técnicas de los artistas: tradición e innovación en la España del siglo XVII», in H. Brigstocke y Z. Véliz (eds.), En torno a Velázquez. Pintura española del Siglo de Oro, exhibition catalogue, London, 1999, p. 30.

15

C. GARRIDO, «Estudio técnico», in Alonso Sánchez Coello y el Retrato en la Corte de Felipe II, exhibition catalogue, Madrid, 1990, pp. 215-243.

16

PACHECO, op. cit. (note 5), p. 481.

17

In fact, we only have evidence that it is also present in one other painting, an anonymous piece, at the Prado Museum, which has matching features in terms of canvas, ground layer and priming layer, King Philip II Offering His Son, Prince Ferdinand, to God after the Victory of Lepanto (P-5226) and in the suite of paintings for the Charterhouse of Granada executed by Juan Sánchez Cotán (1560-1627), a follower of Blas de Prado, which were painted in the first third of the seventeenth century. See M. GÓMEZ and M. JOVER, "Estudio de un conjunto de obras de Sánchez Cotán de la Cartuja de Granada", A report of the Instituto del Patrimonio Cultural de España (hereinafter, IPCE), Madrid, 2003.

18

C. GARRIDO, «Estudio técnico de cuatro Anunciaciones de El Greco», Boletín del Museo del Prado, 23 (1987), pp. 85-108; A. SÁNCHEZ-LASSA y C. GARRIDO, «Estudio técnico», in La Anunciación de El Greco. El ciclo del Colegio de María de Aragón, exhibition catalogue, Museo de Bellas Artes de Bilbao and Museo Thyssen-Bornemisza, Bilbao, 1997, pp. 59-83.

19

Patrimonio Nacional [National Heritage], inv. n.º 10014707. The data referring to works belonging to Patrimonio Nacional has been provided by Pilar Baglietto, Head of the Chemical-Radiological Laboratory of the Department of Restoration of Works of Art at Patrimonio Nacional.

Results: The Change

(Table 2)

Since the beginning of the sixteenth century painters from the north of Italy started to use brownish-red, grey or brownish-grey coloured priming layers, with varying degrees of brightness, on top of a gypsum ground layer20. By the seventeenth century, these coloured oil-based priming layers constituted a practice that had spread right across Italy, and about which there are ample references21.

Juan Fernández de Navarrete, “El Mudo”, was a prominent artist on the Spanish art scene in the second half of the sixteenth century, who trained in Italy –according to the majority of art historians– where he must have had access to the techniques of the great masters prior to his involvement in the El Escorial project22. His death in 1579 interrupted the commission to execute thirty-two canvases for the monastery’s basilica, of which he had only finished seven. Consequently, Alonso Sánchez Coello, Luis Carvajal (1556-1607) and Diego de Urbina (c. 1516- c.1595) were brought in to finish the suite23. The canvas Saints Cosmas and Damian (Patrimonio Nacional, Inv. N. 10034887) –commenced by “el Mudo”, but left unfinished– was completed by Luis de Carvajal and, therefore, is dated in about 1580. The analysis of micro-samples from this painting illustrates the presence of a brownish-red priming layer combining lead white, brown and red coloured earth pigments, charcoal black and traces of azurite, on top of an animal glue ground layer devoid of gypsum. Hence, this is the earliest example yet found of a painting employing the system which would subsequently become the most popular preparation in the following century: an oil-based priming layer without an underlying gypsum ground24.

Another entryway for these new painting techniques, in parallel to Navarrete and his contemporaries who visited and trained in Italy, was the group of Italian painters that came to El Escorial brought there by Felipe II to decorate the monastery. Indeed, some future Hispanic artists –such as Vicente Carducho, of Italian descent, who came to Spain as a child in the company his brother– would be raised in this environment.

The next influential painter in whose oeuvre we encounter a thick, coloured priming layer is Juan Pantoja de la Cruz (c. 1553-1608). Despite being a close follower of Alonso Sánchez Coello in his early years, in the works he paints after the death of his master he favours dark priming layers instead of the light-grey used previously. The three paintings studied, Saint Augustine of Tolentino, A Knight of the Order of Santiago and Queen Margarita of Austria, executed between 1601 and 1606, have dark brown coloured priming layers composed of brown earth pigments, charcoal black, and a small proportion of white lead (fig. 3). Taking into account, from what we know of this artist’s life, that he never visited Italy, this drastic change in his approach to painting can only be explained by his coming into contact with painters like Navarrete and his circle or with the Italians who came to El Escorial.

<p><strong>Table 2.</strong>&nbsp;Datos obtenidos en el Laboratorio de An&aacute;lisis del &Aacute;rea de Restauraci&oacute;n del Museo Nacional del Prado. De no especificarse lo contrario, las obras pertenecen a la colecci&oacute;n de dicho Museo. Se incluye, adem&aacute;s, informaci&oacute;n complementaria que se identifica en las tablas con el siguiente c&oacute;digo: (a) informaci&oacute;n extra&iacute;da de la bibliograf&iacute;a; (b) datos proporcionados por Patrimonio Nacional; (c) datos facilitados por el Instituto del Patrimonio Cultural de Espa&ntilde;a (IPCE). Se indica en negrita el pigmento o material de carga mayoritario en las capas de imprimaci&oacute;n y de aparejo con composici&oacute;n heterog&eacute;nea.</p>

Table 2. Datos obtenidos en el Laboratorio de Análisis del Área de Restauración del Museo Nacional del Prado. De no especificarse lo contrario, las obras pertenecen a la colección de dicho Museo. Se incluye, además, información complementaria que se identifica en las tablas con el siguiente código: (a) información extraída de la bibliografía; (b) datos proporcionados por Patrimonio Nacional; (c) datos facilitados por el Instituto del Patrimonio Cultural de España (IPCE). Se indica en negrita el pigmento o material de carga mayoritario en las capas de imprimación y de aparejo con composición heterogénea.

<p><strong>Fig.3:&nbsp;</strong>Juan Pantoja de la Cruz, Margarita of Austria, Queen of&nbsp;Spain, 1606. 207 x 122 cm (P-2583). The dark-brown&nbsp;priming layer (imprimaci&oacute;n) is visible in the cross-section.</p>

Fig.3: Juan Pantoja de la Cruz, Margarita of Austria, Queen of Spain, 1606. 207 x 122 cm (P-2583). The dark-brown priming layer (imprimación) is visible in the cross-section.

20

The Prado Museum's Laboratory has evidenced the existence of bases coloured in various tones in numerous works by Titian and Tintoretto. See also J. DUNKERTON and M. SPRING, "The development of painting on coloured surfaces in sixteenth century Italy", in Painting Techniques; History, Materials and Studio Practice, IIC Conference Proceedings, Dublin, 1998, pp. 120-130.

21

The Prado Museum's Analysis Laboratory, for example, has been able to evidence the use of this kind of priming layers in works by Caravaggio (The Penitent Saint Jerome, from the Montserrat Monastery Collection), Annibale Carracci (Venus, Adonis and Cupid, P-2631) and Ribera (The Resurrection of Lazarus, P-7768, The Martyrdom of Saint Philip, P-1101). See also A. SÁNCHEZ LEDESMA et al., "Estudio de Materiales" in VVAA, Caravaggismo y clasicismo. La pintura italiana del Museo Thyssen-Bornemisza. Un estudio técnico e histórico, Madrid, 2008, pp. 235-259. L. KEITH "Three paintings of Caravaggio", National Gallery Technical Bulletin, 19 (1998), pp. 37-51. M. D. GAYO et al, "Estudio de materiales", in G. FINALDI (ed.),  Ribera. La Piedad, exhibition catalogue, Museo Thyssen Bornemisza, Madrid, 2003, pp.73-79.

22

R. MULCAHY, Juan Fernández Navarrete «el Mudo», pintor de Felipe II, Madrid, 1999, pp. 5-8.

23

F. B. DOMÉNECH, «La pintura religiosa en Alonso Sánchez Coello», in Garrido, op. cit. (note 15), pp. 114-127.

24

The only painting by Navarrete belonging to the Prado Museum (The Baptism of Christ, P-1012) was executed on a wooden panel, and as such it has not been taken into account for this study. However, we have been able to access analytical data about a painting attributed to Navarrete's circle, Saint Fabian and Saint Sebastian (Diocesan Seminary of Logroño), possessing a similar single brown, oil-based priming layer, but which, curiously, contains a high proportion of gypsum in the mixture. M. GÓMEZ "San Fabián y San Sebastián, círculo de Navarrete", Report of the IPCE, Madrid, 2000.

Results: Development

(Tables 3 and 4)

In the first half of the seventeenth century the use of coloured priming layers would rapidly become widespread, setting the standards, with regard to the practice of painting, which would characterize both the schools of Seville and of Madrid25.

The priming layers used in Seville, represented in this study by the works of Diego Velázquez (1599-1660), Francisco de Zurbarán (1598-1664) and Bartolomé Esteban Murillo (1617-1682), show some distinguishing characteristics, consisting of a composition based on brown coloured earth pigments with a significant amount of calcium carbonate content (either already contained in the earth or added on purpose) as well as a small proportion of charcoal black and white lead (fig. 4)26. The materials match the descriptions found in the treatises by Pacheco and Palomino, including white lead as a siccative27.

Only on rare occasions may a ground layer be detected beneath the brown priming layer, which is quite logical since, as the authors of the treatises point out, it has been reduced to a thin layer of animal glue or some light inert material.

In paintings by the Madrid school the recurrent use of ground layers combining animal glue and calcium carbonate accompanied by small amounts of charcoal black and other minor compounds has been observed28. This medium-grey coloured layer was frequently employed in paintings by various artists in Madrid in the seventeenth century, which leads us to suppose that specialist workshops prepared the canvases for the painters. On top of this grey ground layer, the priming layers used in Madrid possess distinctive red tones composed of earth pigments (ferruginous clays) and small quantities of white lead. Varying proportions of iron found in several points of the same micro-sample suggest the use of a mixture of materials in the manner described in Palomino’s treatise regarding the use in Madrid of finely ground greda or “Tierra de Esquivias” (grey magnesium clay with a low iron content) mixed with brightly coloured red ochre (clay with a high iron content)29.

These red priming layers are present in numerous works by Velázquez, who substituted the brown priming layers used in Seville when he settled in Madrid (fig.5)30. Other representative artists of this period who have been included in this study are Eugenio Cajés (The Virgin and Child with Angels, 1618 and Adoration of the Magi, c. 1620), Maíno (Saint Dominic in Soriano, 1629) and Pedro Núñez del Valle (Adoration of the Magi, 1631)31.

<p><strong>Fig.4: </strong>Detail of Bartolom&eacute; Esteban Murillo, <em>Immaculate Conception of Los Venerables</em> &#39;, c. 1678. 274 x 190 cm (P- 2809). The brown colour, typical of Seville priming layers may be seen particularly around the edges of the figures. This brown priming layer (<em>imprimaci&oacute;n</em>), several coats thick, can be observed in the cross-section. Brown coloured earth pigments, with a low iron oxide and pyrite content, as well as a high amount of calcium carbonate and small proportions of white lead, are detected in the EDX spectrum.</p>

Fig.4: Detail of Bartolomé Esteban Murillo, Immaculate Conception of Los Venerables ', c. 1678. 274 x 190 cm (P- 2809). The brown colour, typical of Seville priming layers may be seen particularly around the edges of the figures. This brown priming layer (imprimación), several coats thick, can be observed in the cross-section. Brown coloured earth pigments, with a low iron oxide and pyrite content, as well as a high amount of calcium carbonate and small proportions of white lead, are detected in the EDX spectrum.

<p><strong>Fig.5:&nbsp;</strong>Detail of Diego Vel&aacute;zquez, <em>The Triumph of Bacchus</em>, or&nbsp;<em>the Drinkers</em>, 1628-1629. 165 x 225 cm (P-1170). The red&nbsp;colour of the priming layer (imprimaci&oacute;n) shown in the&nbsp;cross-section of the micro-sample is clearly visible in the&nbsp;background and edges around Bacchus&rsquo;s head. Red&nbsp;coloured earth pigments, with a high iron oxide content, as&nbsp;well small proportions of white lead, are detected in the&nbsp;EDX spectrum of the analysis performed on the priming layer.</p>

Fig.5: Detail of Diego Velázquez, The Triumph of Bacchus, or the Drinkers, 1628-1629. 165 x 225 cm (P-1170). The red colour of the priming layer (imprimación) shown in the cross-section of the micro-sample is clearly visible in the background and edges around Bacchus’s head. Red coloured earth pigments, with a high iron oxide content, as well small proportions of white lead, are detected in the EDX spectrum of the analysis performed on the priming layer.

<p><strong>Table 4.</strong> Development: School of Madrid.</p>

Table 4. Development: School of Madrid.

<p><strong>Table 3.</strong> Development: School of Seville.</p>

Table 3. Development: School of Seville.

25

The terms "Madrid School" and "Seville School" refer here solely to geographical location, without making reference to stylistic traits. The information to which we had access and the data directly obtained from the Prado Museum's Analysis Laboratory did not permit us to include data related to other local schools.

26

A. ILLÁN et al., «Características de las preparaciones sevillanas en pintura de caballete entre 1600 y 1700: implicaciones en el campo de la restauración y la historia del arte», in II Congreso GE-IIC: Investigación en Conservación y Restauración, Barcelona, 2005, pp. 197-205; C. GARRIDO, Velázquez: técnica y evolución, Madrid, 1992, pp. 67-87 y 97-111; J. MARTÍNEZ BLANES et al., «Estudio científi co de muestras procedentes de pinturas de Francisco Zurbarán en el Museo de Bellas Artes de Sevilla», III Congreso Nacional de Arqueometría, Sevilla, 2001, pp. 159-169; R. BRUQUETAS et al., «La conservación de dos pinturas de Zurbarán de la capilla de San Jerónimo del Real Monasterio de Guadalupe», X Congreso de Conservación y Restauración de Bienes Culturales, Cuenca, 1994, pp. 445-453. A. SÁNCHEZ LASSA, «Entre Sevilla y Madrid: aportación al estudio de la técnica de Zurbarán», in Zurbarán, la obra final: 1650-1664, exhibition catalogue, Bilbao, Museo de Bellas Artes de Bilbao, 2000, pp. 129-148; V. MUÑOZ y F. DE LA PAZ, «Murillo joven: aportación al conocimiento de su técnica», in B. NAVARRETE y A.E. PÉREZ SÁNCHEZ, El joven Murillo, exhibition catalogue, Museo de Bellas Artes de Sevilla, 2010, pp. 165-178; A. SÁNCHEZ LASSA, «San Pedro en Lágrimas. Aproximación a la técnica de Murillo», in A. SÁNCHEZ LASSA and A.E. PÉREZ SÁNCHEZ, Las lágrimas de san Pedro en la pintura española del siglo de Oro, exhibition catalogue, Museo de Bellas Artes de Bilbao, Bilbao, 2000, pp. 71-81.

27

PACHECO, op. cit. (note 5), p. 481 and PALOMINO, op. cit. (note 5), p. 130.

28

This composition may correspond to one of the ground layers mentioned by both Pacheco and Palomino which consisted of sifted ash ("cernada"). According to Pacheco, this type was specifically used in Madrid. The high percentage of calcium, higher than the charred remains of coal and/or wood, might be an additive designed to give this layer more body. The remaining elements presents are (in proportional order): silica, phosphorous, potassium, aluminium, sulphur, iron and magnesium. PACHECO, op. cit. (note 5), p. 481 and PALOMINO, op. cit. (note 5), p. 134.

29

PALOMINO, op. cit. (note 5), p. 130.

30

GARRIDO, op. cit., (note 26), pp. 113- 203; L. KEITH y D. CARR, «Velazquez’s Christ after the flagellation: technique in context», The National Gallery Technical Bulletin, 30th anniversary volume, London, 2009, pp. 52-69.

31

In Rafael Romero's study of the Spanish bodegón numerous examples of seventeenth paintings from Madrid are included, in which the same system of ground and priming layers described here is employed. R. ROMERO, «El bodegón español en el siglo XVII: desvelando su naturaleza oculta», Icono I&R, Madrid, 2009.

Results: Exceptions

(Table 5)

In seventeenth century painting there are some exceptions to this general rule of using coloured priming layers with varying degrees of dark tones. This is the case of Maíno, who on numerous occasions painted directly onto a thick, light-greyish, ground layer, of a similar composition to the kind used in Madrid. Only in a few works does he use differently coloured priming layers: medium-grey for Adoration of the Shepherds and for Adoration of the Magi from the Cuatro Pascuas altarpiece, red for Saint Dominic in Soriano and practically white for The Recovery of Bahía de Todos los Santos32.

Vicente Carducho also preferred light backgrounds for his paintings, as can be seen from the suite of Carthusian scenes he painted for the Monastery of Paular (1626- 32), The Holy Family (1631) and from The Capture of Rheinfelden (1634-35), which he painted for the Hall of Realms. The paintings at El Paular and The Holy Family have a light brown coloured oil-based priming layer made of reddish and brown earth pigments with a low iron content and a high proportion of magnesium33, as well as small amounts of white lead added as a siccative. Regarding his painting for the Hall of Realms its priming layer has a similarly light tone and is also executed in oil (fig.6). However, on this occasion the main component is gypsum, accompanied by earth pigments with low iron and magnesium content, and a small proportion of white lead.

Despite the fact that Carducho recommends using gypsum to prepare canvases in his Diálogos de la Pintura, this material has not been identified in the ground layers beneath the oil-based priming layers in the group of works by the same artist at the Prado Museum34. One possible explanation for the wide variety of materials sometimes employed in a single artist’s oeuvre is the existence of independent professional workshops commissioned for the preparation of canvases for painting, which meant artists did not necessarily know the exact composition of the layers when they purchased them. As we mentioned earlier, both Carducho and Palomino refer to this in their texts35.

<p><strong>Fig.6:&nbsp;</strong>Chromatogram of the binder of the priming layer obtained by GS-MS of Vicente Carducho&rsquo;s painting <em>The Capture of Rheinfelden</em>, 1634. 297 x 357 cm (P-637). The relative proportions of azelaic, palmitic and stearic acids indicate it is linseed oil.</p>

Fig.6: Chromatogram of the binder of the priming layer obtained by GS-MS of Vicente Carducho’s painting The Capture of Rheinfelden, 1634. 297 x 357 cm (P-637). The relative proportions of azelaic, palmitic and stearic acids indicate it is linseed oil.

<p><strong>Table 5.</strong> Exceptions.</p>

Table 5. Exceptions.

32

The use of a grey priming layer found in works from Toledo could be said to be a common pictorial practice employed by the Toledan artistic milieu. The grey colour is similar to the priming layer employed by Blas de Prado, but Maíno, for example, used a greater variety of pigments by incorporating palette leftovers to the mix.

33

This high level of magnesium content is a constant in the priming layers of works executed from 1626 to 1632 that have been studied by the Prado Museum Analysis Laboratory. This fact may perhaps be more related to the origin and qualities of the pigments supplied to Carducho's studio during this period than to the express wishes of the artist.

34

On the contrary, according to Illán and Romero, in all of the sketches of this same suite, a gypsum and animal glue ground layer has indeed been detected; see A. ILLÁN and R. ROMERO, «El proceso creativo de Vicente Carducho, con especial referencia a los bocetos para el ciclo pictórico sobre la orden de los cartujos (monasterio de El Paular)», Ciencia y esencia. Cuadernos de conservación y tecnología del Arte, vol. I, Madrid, 2008, p. 15.

35

CARDUCHO, op. cit. (note 5), p. 299 and PALOMINO, op. cit. (note 5), p. 134.

Results: The Hall of Realms

(Table 6)

The decoration of the Hall of Realms of the Buen Retiro Palace has been studied in detail36. It has been possible to analyse the priming layers of eight of the group of works painted to decorate it –two equestrian portraits and six battle scenes– by Eugenio Cajés, Carducho, Maíno, Antonio de Pereda (1611-1678), Velázquez and Zurbarán.

When Velázquez returned from Italy at the beginning of 1631, he undertook to change his painting technique again, a change he would maintain until the end of his life, introducing light-toned, whitish, greyish or pinkish priming layers for which the common denominator and main pigment was white lead37. In the works he painted for the Salón de Reinos, both The Surrender of Breda and the equestrian portraits, he used a light-grey priming layer (fig. 7)38.

Curiously, most of the artists who took part in the commission opted for a similar solution, even though it was not their usual technique. Cajés, for example, changed the colour and composition of his priming layer quite radically compared to his other works (see table 4) and Maíno, who often painted directly on top of a greyish ground layer, on this occasion covers his canvas with a much lighter, almost white, priming layer (fig. 8). Pereda, the youngest of the group, also uses a practically white-coloured base, applied almost directly onto the canvas, and Zurbarán too lightens the tone of the priming layer for his work The Defense of Cadiz against the English compared to the dark brown one he habitually employed in his paintings39. Solely in the piece The Capture of Rheinfelden, by Vicente Carducho, the identified materials differ from the rest. This artist remains faithful to his customary technique of painting on top of light-toned neutral bases preferring this to the use of lighter priming layers by the rest of the group.

In light of these results, one can speculate about Velázquez’s influence when it came to planning this joint effort which needed not only to convey a unified message in relation to the subject matter, but also to achieve a similar artistic style. Taking into account that all of the paintings depicted outdoor scenes for which the usefulness of a light base is justifiable, it is possible there was a degree of agreement or even specific guidelines to follow in this regard. Carducho’s custom of working on light backgrounds meant he could carry on without changing his usual technique, though he is loath to follow the rest of the painters who lighten them even more.

<p><strong>Fig.8:&nbsp;</strong>Fray Juan Bautista Ma&iacute;no, <em>The Recovery of Bah&iacute;a de Todos los Santos</em>, 1634-35. 309 x 381 cm (P-0885). The crosssection of the micro-sample shows the ground layer (aparejo) and the off-white priming layer (imprimaci&oacute;n). The latter is visible through the painted surface around the woman&rsquo;s profile (detail).</p>

Fig.8: Fray Juan Bautista Maíno, The Recovery of Bahía de Todos los Santos, 1634-35. 309 x 381 cm (P-0885). The crosssection of the micro-sample shows the ground layer (aparejo) and the off-white priming layer (imprimación). The latter is visible through the painted surface around the woman’s profile (detail).

<p><strong>Fig.7:&nbsp;</strong>Detail of Diego Vel&aacute;zquez&rsquo;s <em>Equestrian Portrait of Felipe III</em>, 1635. 307 x 367 cm (P-1176). The cross-section of the micro-sample of the painting clearly shows a very light-toned priming layer (imprimaci&oacute;n) beneath the layer of blue paint, which confers the painting great luminosity.</p>

Fig.7: Detail of Diego Velázquez’s Equestrian Portrait of Felipe III, 1635. 307 x 367 cm (P-1176). The cross-section of the micro-sample of the painting clearly shows a very light-toned priming layer (imprimación) beneath the layer of blue paint, which confers the painting great luminosity.

<p><strong>Tabla 6.</strong>&nbsp;The Hall of Realms.</p>

Tabla 6. The Hall of Realms.

36

J. BROWN and J. ELLIOT, Un palacio para el rey. El Buen Retiro y la corte de Felipe IV, Madrid, 2003; J. ÁLVAREZ LOPERA, «La reconstitución del Salón de Reinos. Estado y replanteamiento de la cuestión», in El Palacio del Rey Planeta. Felipe IV y el Buen Retiro, exhibition catalogue, Madrid, Museo Nacional del Prado, 2005, pp. 91-167.

37

Some authors have suggested Velázquez's use of this light inner layer may have originated from direct knowledge of Ruben's painting technique during his sojourn in Madrid in 1628, immediately before he departed for Italy. In effect, the use of white lead in priming layers has been detected in various works made by Rubens in Madrid (the Prado Museum's Immaculate Conception P-1627, Adam and Eve P-1692 and Rape of Europe P-1693). On the other hand, this type of priming layer was a customary aspect of the Flemish artist's technique in all of the works he painted in his own country. See G. MCKIMSMITH and R. NEUMAN, Ciencia e historia del arte. Velázquez en el Prado, Madrid, 1993, pp. 57; N. VAN HOUT, «Meaning and development of the ground layer in seventeenth century painting», in E. HERMENS (ed.), Looking through paintings: the study of painting techniques and materials in support of art historical research, London, 1998, pp. 199-217; KEITH and CARR, op. cit. (note 31), p. 67- 69. In the biographical information we consulted regarding the technique of Italian painters at the time when Velázquez visited Rome, priming layers are described as dark and mainly made of earth pigments. See note 22 and E. MARTIN, «Grounds on canvas 1600-1640 in various European artistic centers», en J. TOWNSEND et al. (eds.), Preparation for Painting, London, 2008, pp. 63-64.

38

In addition to the data about these pieces obtained from the Prado Museum's Laboratory, Carmen Garrido has compiled information about all of the paintings from this period in her book: GARRIDO, op.cit. (note 26), 1992, pp. 321-383.

39

There is still no data available about the ten scenes of The Tasks of Hercules painted by Zurbarán for this same room, therefore one cannot evaluate whether the artist employed a light priming layer for these paintings too, or if this was reserved for large-scale formats only.

Results: Continuity of the Madrid School

(Table 7)

With the aim of evaluating whether there was a continuity regarding the usage of these light priming layers, three works painted after Velázquez’s death have been included in this study: The Empress Margarita of Austria (1666), by Juan Bautista Martínez del Mazo (c. 1612-1667) as well as two paintings by Juan Antonio Escalante (1633-1670), The Explorers of the Promised Land and Noah and his Family after the Flood (both from 1668). The priming layers of these paintings, very similar in appearance and composition, have a whitish tone, obtained by a mixture of white lead and calcium carbonate, with small amounts of earth pigments and charcoal black. As such, it would appear in these specific cases that Velázquez’s influence has been an enduring one to some extent. This is quite logical for Mazo, bearing in mind his closeness to the master, but not for Escalante, who had more affinities with the circle of Francisco Rizi (1614-1685).

It is not possible to chart the spread of the use of whitish priming layers outside of Velázquez’s circle in Madrid in the seventeenth century based on the data available to us today40. In fact, the traditional red priming layers of the Madrid School continue to be used concurrently41 and we can even find them used in works from the end of the century, like the ones painted Luca Giordano42, and they were still employed in subsequent centuries. In this regard, the account of Palomino, a painter active in this same period, which describes the red priming layer as the most popular one used in Madrid, is very relevant.

<p><strong>Table 7.</strong>Continuity of the Madrid School.</p>

Table 7.Continuity of the Madrid School.

40

The Prado Museum houses an important collection of Spanish painting from the end of the seventeenth century, but there is still not much analytical data about the composition of their priming layers. Literature about this period is not very informative in this regard either.

41

The book by Rafael Romero features an analysis of a number of bodegones executed in Madrid at the end of the century among which are a few examples of white priming layers (Juan de Arellano and Pereda, for instance), as well as describing numerous works still employing the classic Madrid-style ground layer described for the early years of the century, R. ROMERO, op.cit.(note 31), pp. 293-386.

42

M.D. GAYO, «Materiales identificados en un grupo de obras de Luca Giordano pertenecientes a la colección del Museo del Prado», in A. ÚBEDA DE LOS COBOS (ed.), Luca Giordano. Técnica. Pintura mural. Actas del congreso internacional, Madrid, 2010, pp. 125-130.

Conclusions

A change occurred in oil painting techniques during the sixteenth and seventeenth centuries: we witness a gradual reduction of the ground layer until it practically disappeared, and encouraged an increasingly thicker and more colourful priming layer. Little by little the ground layer was reduced to an extremely thin sizing layer, on top of which the priming layer was extended.

This change took place gradually and was not adopted by all artists to the same degree. As time went by, gypsum ground layers fell into almost complete disuse, although they sometimes still cropped up in an exceptional manner in a few works.

Priming layers are mainly composed of earth pigments for a variety of reasons: these materials were cheap and easily available, their drying capacity was acceptably fast in a oil medium and, furthermore, they provided the painter with a suitable tone to facilitate the creative process, a coloured base on which to create backgrounds or halftones. Italian painters had an evident influence on the adoption of coloured priming layers in Spanish painting, both through the trips undertaken to Italy by local artists and thanks to their relationship with the group of Italians who worked at El Escorial. Navarrete, “el Mudo”, is the first Spanish painter of the group studied in which we have detected the use of the new practice. Interestingly, El Greco, in keeping with his Venetian training, regularly employed coloured priming layers in his entire oeuvre, but he continued to use an underlying gypsum ground layer even in his late works, an approach that has already become anachronistic compared to the majority of his peers.

Both the Seville School and the Madrid School of the seventeenth century display consistent approaches to the preparation of canvases , apart from exceptions such as Maíno and Carducho. These techniques would endure with only slight variations throughout the entire century, an example in point being Velázquez’s late period.

In addition to this, it has been proven that for the most part the information about oil painting techniques and materials contained in the art treatises of the period agrees with the results obtained from the analysis of micro-samples. This corroborates the usefulness of said studies for improving knowledge about the techniques employed by the artists.Lastly, it is very interesting to note the use by various artists of very light priming layers in the battle scenes painted to decorate the Salón de Reinos at the Buen Retiro palace, which was contrary to their customary approach. Taking into account that Velázquez used this type of base for his paintings after he returned from Rome in 1630, it does not seem far-fetched to speculate about his influence on the rest of the group, in some way or another setting the general guidelines to follow. This indicates, in this instance at least, that these artists were willing to vary their customary technique and to try out new methods in order to achieve different artistic effects in their work, regardless of the dictates of tradition or of what they had learned from their masters.

Acknowledgements

The authors would like to thank Ángel Balao and Pilar Baglietto at Patrimonio Nacional and Rocío Bruquetas, Marián del Egido and Marisa Gómez at IPCE for the useful information they provided. The authors are also very grateful for the support they received from Pilar Sedano, former Head of the Conservation Department at the Prado Museum and the help they received from the staff at the museum, in particular Carmen Garrido and her colleagues at the Technical Documentation Department, Solenne Gaspard, Javier Portús and Leticia Ruiz. The English translation has been done by Tom Skipp and the final review of the English text by Tiarna Doherty and Gabriele Finaldi.

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