For here thou must know that daily experience in Alchymie doth shew, that any dead earth, or _Caput Mortuum_, as soon as it comes out of the Fire into the Aire, doth quickly get another colour, and leaves its own colour which it got in the fire. For the changes of those colours are various. For as the matter is, so are the colours that are made, although for the most part they flow from the blacknesse of the dead earth. For you that are skilful in Alchymie see that the dead earth of _Aqua fortis_ comes black from the Fire, and by how many more ingredients there bee in it, by so much the more variously doe the colours shew themselves in the Aire: sometimes they seem red, as Vitriall makes them: sometimes yellow, white, green, blew: sometimes mixt, as in the Rainbow, or Peacocks taile. All those colours shew themselves after the death, and by the death of the matter. For in the death of all naturall things here are seen other colours, which are changed from the first colour into other colours, every one according to its nature, and property. [Sidenote: The preparation of Verdegrease to be used in Alchymie.] Now we wil speak of that Verdegrease which is to bee used in Alchymie. The preparation, and processe of that is this. Make very thin plates of Copper, strow upon them Salt, Sulphur, and Tartar ground, and mixed together, of each a like quantity in a great calcining pot. Then reverberate them twenty foure houres with a strong Fire, but so that the plates of Copper do not melt, then take them out, and break the pot, and set the plates with the matter that sticks to them into the Aire for a few dayes, and the matter upon the plates wil bee turned into a faire Verdegrease, which in all sharp Corroding waters, waters of Exaltation, and in Cements, and in colouring of Gold, doth tinge Gold, and Silver with a most deep colour. [Sidenote: How Æs vstum, or Crocus of Copper is to be made.] Now to turne Copper into _Æs ustum_, which is called the _Crocus_ of Copper, the processe is this: