Faldoni, parts 2424 - 2427

 2424. From Cennini’s Artists Handbook: How to prepare Ultramarine Blue pigment: First take some lapis lazuli; and if you would know how to distinguish the best stones, take those which contain most of the blue color, for it is mixed with what is like ashes. That which contains least of this ash pigment is the best.

 2425. Pound it in a covered bronze mortar so that the powder may not fly away; then put it on your slab of porphyry, and grind it without water. Afterwards take a covered strainer like that used by the druggists for sifting drugs and spices, and sift it and pound again as much as is required.

 2426. Once the powder is prepared, procure from the druggist, six ounces of resin of the pine, three ounces of mastic, and three ounces of new wax to each pound of lapis lazuli. Put all these ingredients into a new pipkin and melt them together. Then take a piece of white linen and strain these things into a glazed basin. 

2427. Then take a pound of the powder of lapis lazuli; mix it all well together into a paste, and that you may be able to handle the paste, take linseed oil, and keep your hands always well anointed with this oil. This paste must be kept at least three days and three nights, kneading it a little every day; and remember that you may keep it for fifteen days or a month, or as long as you please. When you would extract the azure (blue) from the paste, proceed thus.