EL GRECO From Italy to Toledo

The identification of two different types of lead-tin yellow points to a significant change, which can probably be attributed to the local materials of the region where El Greco painted the work. Lead-tin yellow is a synthetic pigment that was widely used from the 14th to 18th centuries, and its two known varieties have different stoichiometric ratios and origins. Lead-tin yellow type I is a double oxide of lead and tin whose formula is Pb2SnO4, and lead-tin yellow type II is another type of oxide that follows the general formula Pb(Sn,Si)O3. Type II can be obtained by fusing lead-tin yellow type I with silica at a temperature of 800-950ºC. Different analytical studies have proven that type I is the most commonly used variety, although type II is older and has been identified quite frequently in works from Florence, Venice and Bohemia, suggesting that it may have originated in connection with the glass industry. Chemical analyses performed on Spanish paintings suggest a greater tendency to use lead-tin yellow type I.

Scanning and transmission electron microscopy are both effective techniques for classifying these pigments. However, with the latter the compound's crystal structure can also be studied, allowing us to determine the variety of the pigment with greater accuracy.