Used by 15th and 16th century masters, Naples yellow was thought to be a lead antimonial by de Fougeroux (1766). A 1790 work, Secrets of Arts and Crafts, gives two methods of preparation, one used at Sevres, the other at Naples. In 1941, R. Jacobi, discovering not antimony but tin, defined it as a compound of lead protoxide, lead orthoplombate or lead bioxide and metastannic acid. Most modern authors place it not among stannates but antimonials of lead. Confused sometimes with Merimee yellow, or Cassel yellow, the term Naples yellow does not correspond to a definite chemical compound, hence the variations in pigmentation.