Rubification

These colors come and go, as heat is administered approaching to the third degree, till all is of a beautiful green, and as it ripens assumes a perfect whiteness, which is the White Tincture, transmuting the inferior metals into silver, and very powerful as a medicine. But as the artist well knows it is capable of a higher concoction, he goes on increasing his fire till it assumes a yellow, then an orange or citron color; and then boldly gives a heat of the fourth degree, till it acquires a redness like blood taken from a sound person, which is a manifest sign of its thorough concoction and fitness for the uses intended.

“On The Philosopher’s Stone”