From The Book of Quintessence:

First, reduce gold into calx as I have related before. Then take distilled vinegar or old urine (that has no feces in it) and put it into a glass vessel. The liquid should be at a height of four inches. Put the calx of gold into this and set it under strong sunlight in summertime. You will soon see a liquid like oil ascend to the top as a film. Gather that film with a small spoon or a feather and put it into a glass vessel that already has water in it. Gather it thus many times in the day until it no longer ascends. After pooling the samples, evaporate the water via heating. The quintessence of the gold will stay behind. Many philosophers call this quintessence an incombustible oil. That is a great secret.

If you fix this quintessence in our heaven [the 1000-time distilled "mortal heaven" outlined previously] it will without doubt restore a man again to his lost faculties and restore the virtues of the strength of youth and also lengthen his life into the last term of life set by God.

Now, I have told you the greatest secret and restoration of mankind. This great thing must not be displayed. For this oil, that is to say quintessence of gold, has extreme powers to soothe and remove the ache of wounds and to heal wounds, old sores, and many horrible evils.

You may also draw quintessence out of silver in the same manner.