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Secret of Secrets (Sirr al-Asrar)

This is al-Razi's most famous book. Here he gives systematic attention to basic chemical operations important to the history of pharmacy. In this book al-Razi divides the subject of " matter ' into three categories, as in his previous book Al-Asrar.

Similar to the commentary on the 8th century text on amalgams ascribed to Jabir ibn Hayyan, al-Razi gives methods and procedures of coloring a silver object to imitate gold (gold leafing) and the reverse technique of removing its color back to silver. Gilding and silvering of other metals (alum, calcium salts, iron, copper, and tutty) are also described, as well as how colors will last for years without tarnishing or changing.

Al-Razi classified minerals into six divisions:

Al-Razi gives also a list of apparatus used in alchemy. This consists of 2 classes: