Glassmakers made sulphides by encasing pure white ceramic plaques - usually molded portraits of famous people - in glass. In the 19th century, the most popular subjects were probably Napoleon I and Queen Victoria. Sulphides were tricky to produce. First, the wafer-thin decoration had to be carefully molded, removed from the mold, and dried. Any excess clay had to be trimmed away without damaging the fragile sulphide. It was then fired and, while hot, inserted into a small bubble of molten glass. Finally, the bubble was collapsed around the sulphide by sucking out the air. Some manufacturers poured molten glass directly onto the heated sulphide. It is evident that, however careful they were, glassmakers could not avoid spoiling some of the sulphides. Cracking must have been the most prevalent problem.