Verdigris or Calx of Venus
Verdigris is a green or bluish substance, almost insoluble in water but very soluble in vinegar and other acid spirits. Verdigris is formed on the surface of copper or brass parts that are exposed to the action of humid air and is nothing else than a copper carbonate. Copper carbonate, in its natural state, is malachite.

Frequently, verdigris is confused with copper acetate.

Seek 1 kg of native Venus vitriol; place it inside a glass or porcelain recipient and pour in well water heated up to 40º C, enough to dissolve it completely. Then filter the solution.

In an enamelled iron basin, dissolve separately, in source water heated to 40º C, 1 kg of salt of tartar (potassium carbonate) or, if you do not have it, use sodium carbonate. Filter the solution.

Now, plunge a porcelain or enamel mug into the vitriol solution and fill it. Pour it, little by little, into the carbonate solution. There is an effervescence. Stir well with a wooden spoon, and a precipitate of a clear green-blue colour will be begin to form.

Proceed in the same way, stirring continuously, until the effervescence stops. If there is no more effervescence when you pour the vitriol solution, it is because the solution is saturated. Then, stop.

Leave it to rest some time, then decant the solution. If it a bluish liquid is drained, it is because there is still some vitriol in the solution that did not react with the carbonate.

Pour an abundance of tap water on your precipitate to wash it thoroughly, always stirring the liquid well, until the water comes out clear.

By decantation, pour off the water and let it evaporate in the sun or on a gas stove, with moderate heat, in a sand bath.

When the matter is dry, remove it with a stainless steel spoon and store it in a large mouth glass flask that is stoppered well closed.

This canonical verdigris of Venus, although prepared artificially, was made of native Venus vitriol, which is the main element of the chemical reaction.

Calx of Venus. If you want to prepare the calx of Venus or Aes Ustum (oxide), put 250g of verdigris in a earthenware or stainless steel porringer and place it on a gas stove at a very high heat. Move or stir well again with a stainless steel spoon, as if you where to calcinate it, until it turns completely black. When it reaches this point, stop and let it cool. Proceed in the same way, until you have calcinated all of your verdigris. When cool, pour it in a large mouth glass flask and stopper it well closed.

This calx will serve you to you prepare the verdigris and the tincture of Venus.

Rubellus Petrinus