Résumé
A new procedure for the production of red gold purples was developed at the "Manufacture de Sevres" for the production of high-quality red gold enamels. A significant improvement in the synthesis of the red gold purple no 601 compared to the historical method used since the 18th century was achieved by optimising, on physico-chemical bases, the conditions of synthesis of the starting gold colloid. In particular, the use of a purer tin precursor, a better control of the reaction times and of the pH conditions via the use of a hydrogenocarbonate buffer allowed a complete control of the tint of synthesised purple and of the resulting red enamel. This method allows the completely reproducible synthesis of consecutive batches of a constant red colorant, which ultimately permits a standardisation in the amount of gold added into other gold-containing enamels (more than 8 other enamels). Compared to the other red enamels synthesised throughout his whole history, the new no 601 can be classified among the most beautiful and valuable red enamels ever produced at the "Manufacture de Sevres".