Famous Rozenburg eggshell

I show you a fine example of a masterpiece of Eggshell porcelain with 2 parrots. Unfortunately it's broken but nevertheless a great piece;

HISTORY OF EGGSHELL
Eggshell porcelain is named after the skin of the shard, which is so extremely thin that it is slightly transparent. Many experts have racked their brains over the question whether the material was real porcelain. Originally it was assumed that the pigments of the decorations couldn't withstand temperatures of over 1300 degrees C. This led to the conclusion that the material must have been baked at lower temperatures, and could therefore not be porcelain. Porcelain - which first got its name from Marco Polo (1254-1324) - was already developed in China in 600-900 AD. The production method of this popular material had been shrouded in mystery for centuries, and Europe had to rely on import from Asia until, in the early 1700s, J.F. Bottger invented the European hard-paste porcelain. Notably, this variety was baked at much higher temperatures than the Chinese material: 1370-1460 degrees C against 1000-1320 degrees C. Not everyone was charmed by this hard-paste porcelain (which the English call Dresden China) and in a number of countries softer material was developed, which - after the Chinese example - was baked at lower temperatures, e.g. in Scandinavia, in France (Pate Nouvelle) and in England (Bone China). After a few failures with Bone China, Kok started to experiment with a material that had been developed by Prof. Dr. H. Seger in Berlin. Which of the two types of porcelain clay he actually used is not entirely clear, but in the factory archives the composition was found: 19% Cornwell stone, 31,6% china clay, and 49,4% bone meal. With information from that same archive, 'Kok's secret' was also unlocked. In order to better conserve the decorations, he turned the traditional process around, ordering the biscuit heating (of the bare shard) to take place at very high temperatures, up to ca. 1500 degrees C, while the polish heating (of the glazed shard) took place at a lower temperature. Ergo, we can qualify eggshell porcelain as porcelain, on the grounds of the baking temperatures.