State of preservation
The miniatures' state of preservation varied considerably and depended on the work in question. Deterioration partly derived from natural aging but the most serious damage was the result of inappropriate restoration in the past and poor handling.
Changes of relative humidity and temperature influence the natural aging of a miniature given that ivory is a hygroscopic material and atmospheric changes can thus result in warping and twisting fig. 28. When the ivory twists out of shape it is counter-productive to attempt to return it to its original form given that its composition involves an inorganic, rigid part called cementum that may crack or split if forced back into shape. In numerous cases the twisting and splits in the miniatures resulted from tensions produced by frames or support systems that prevented the natural movement of the ivory or from the fact that the works were originally stuck down onto thick sheets of card fig. 17.
Another intrinsic problem is the sulphuration of the silver leaf, which is a corrosion that changes the colour of the metal, making it irregularly darker. These darkened spots show through in the flesh tones and produce shadows that disfigure the face. In the present day when this problem is encountered with miniatures that retain their original sheet of silver leaf, the sheet is not removed as restorers apply the criterion of conserving the work intact and hence the materials from which it is made. In addition, no miniature in the Prado's collection had darkened patches that were so serious as to disfigure the fact and thus raise the issue of removing the metal sheet. However, old restoration procedures did involve removing these sheets and in order to do so the pieces of paper and other types of protective backing were also removed. In such cases the modern response has been to insert a loose sheet of aluminium, as this is a more stable metal and produces the same optical effect as the old silver sheets. Juan Pérez de Villamayor's Portrait of a Lady with Flowers in her Hair and a green Dress (O-699) has a silver-plated copper sheet in which the edges had become sulphurated. As the metal sheet was loose it had moved and the darkened edge was now located behind the sitter’s forehead, producing a dark patch that disfigured the image. In order to correct this it was only necessary to move the sheet back to its original position fig. 19. Miniatures were also encountered in which the silver leaf had been completely stuck down with a gum adhesive or protein-based glue that resulted in more significant damage as the silver in contact with the glue oxidised far more and resulted in larger dark areas on the face fig. 18.