Dictionarium polygraphicum. The way of preparing the transparent verdegrease is as follows.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
Take six ounces of common verdegrease (the distill'd verdegrease will not answer this purpose so well) break it into little pieces, and boil it gently in a quart of white wine vinegar, keeping continually stirring it; when you perceive it to boil, add a little tartar broken, continuing still to stir it, till you perceive the liquor of such a colour as you would have it, i. e. till it is of a fine transparent Green, with a bluish cast, which you may know by dipping in a bit of white paper.

Then pour it through a linen cloth into an open vessel, and set it to cool, and when it is quite cold, keep it in a bottle for use; stop it close, for being expos'd to the air, it will dry; but may be reduc’d again by common water.

This liquor should be touch’d upon part of the lights and shades of a print, and the shades afterwards coloured with Sap green.

N. B. In the making of this Green, be sure to make it strong enough; for it cannot be strengthened afterwards, without the trouble of boiling afresh; but may at any time be rendered as faint as you please, by mixing common water with it.