Support, ivory panels
The small panels of ivory were made by cutting the tusk longitudinally, for which reason its width determined the diameter of the sheet. The largest ivory panel in the Prado's collection is the Portrait of the Infanta Luisa Carlota by Luis de la Cruz y Ríos (O-669), which measures 12.5cm wide. For very large-format works the outside layers of the tusk were sometimes used, which is a rougher, yellower area that can be seen at the edges of some miniatures. fig. 1
The ivory panels are extremely fine, approximately 0.4 to 0.5mm thick, although in works of lesser quality they can be more than 1mm thick. The use of such fine panels was not due to a lack of raw material but to the fact that the translucent, whiteish tone of the ivory was used for the flesh tones. The ivory tone was used as the base while on some occasions a sheet of silver leaf, silver-plated copper or gilt metal was placed behind the miniature as this lit up the flesh tones from behind and increased the depth of the shadows fig. 10. This thin metal sheet was generally only located behind the flesh areas although we have encountered examples in which it was placed behind the entire image. In other cases artists used what was called tiza roja, a piece of red card that “warmed up” the flesh tones and gave the sitter a lively, healthy appearance. When these backing sheets have been lost or have deteriorated, the miniature looses light and the sitters' appearance becomes rather dull and pallid. In the case of the Portrait of the Marchioness of Lazán (O-701), José Alonso del Rivero not only used a sheet of silver leaf but also painted on the back of the ivory panel in order to make the background darker fig. 2
The backs of miniatures were generally covered with a piece of protective paper attached with a few spots of glue, frequently with a piece of vellum on top of it. In other cases, the ivory panel was stuck down onto a thick piece of rigid card that made it safer to handle and to mount in a frame. This system was used in the Portrait of the Infanta Luisa Carlota by Cruz y Ríos (O-669). When the ivory panel is uniformly stuck to the card this provides excellent stability but unfortunately, on some occasions, particularly when later restoration has been carried out, only one side is stuck down, as a result of which the ivory has become distorted in the area around the adhesive.