The most valuable secret an 18th-century porcelain manufacturer possessed was his recipe for making porcelain paste. Each factory's porcelain has its own particular quality and color. Despite the secrecy that surrounded these formulas, an analysis of the soft-paste porcelain of each of the Big Four factories strongly suggests that information was leaked to the competition. The formulas were strikingly similar in terms of composition and ingredients, and in some cases varied no more than a few hundredths of a percentage.
Not only did the Big Four try to steal each other's porcelain formulas, they were also keenly interested in each other's recipes for enamel glazes and colors. The colors used by each factory, which depended upon the maker's know-how and technology, can help identify the origin of a snuffbox.
For the most part, the "Big Four" factories were able to maintain relatively tight control over their employees. Very often the terms of the company's royal privilege would impose prison sentences on employees if they tried to defect to another factory. They did, however, enjoy a number of privileges not granted to other types of workers, such as being exempt from paying certain taxes.
Above: Backstamps of three of the "Big Four" porcelain factories in France.