Dictionarium polygraphicum. Verdigris, verdegrease.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol II.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
Verdigris, verdegrease is a kind of rust of copper, of considerable use in painting for green colour. It is a preparation made of plates of copper, and the husks of grapes well-saturated with wine, put up in earthen pots, and dispos'd layer upon layer, i. e. first husks and then copper; and this repeated 'till the vessel is moderately fill'd.

These pots are afterwards set in a cellar, where they are let to stand sometime, and then taken out, to gather the verdegrease, which is a green rust, with which the plates are covered all over.

The greatest part of the verdegrease us'd in Europe, comes from Languedoc in France, being made of the husks of the grapes of that country, and is brought over in cakes of about twenty-five pound weight.

The crystalliz'd verdegrease, or crystals of verdegrease, or calcin'd or distill'd verdegrease, is verdegrease dissolv'd in distill'd vinegar, and afterwards filtred, evaporated, and crystalliz'd in a cellar. This is us'd by painters to make a green colour, especially in miniature; it makes a beautiful transparent green for japanning on glass, being ground with oil of turpentine, and mix'd with common varnish, and leaf-gold or silver laid on the backside of it.

This commonly comes from Holland, or Lyons in France, and on sticks in form like our sugar-candy. To be good, these crystals must be beautiful, clean, and transparent, very dry, and as feee from sticks as possible.

Crystals of verdegrease are likewise made by dissolving copper, granulated in spirit of nitre, and afterwards evaporating to a scum or pellicle, and setting it in a cellar to crystallize.

Verdegrease is the plague of all colours, and enough to spoil a whole picture in oil-painting, if the least part of it enters into the priming of the cloth, yet 'tis a beautiful and agreeable colour; sometimes 'tis calcinated to take off its malignity; but 'tis dangerous to calcinate, as well as red arsenick; and let it be ever so well purified, it must be used alone, for it will spoil all the colours that are mix'd with it.

It is made use of, because it dries very much; and only a little of it is us'd, mix'd in blacks, which never dry alone.

The painter ought to take care, that he does not use the pencil with which he painted verdegrease in any other colours.

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