The Green-Colour, made of Copper-rust, commonly called Verdegris, tho' ground in Oil, will not fail to evaporate in Smoke, and lose its Beauty, unless you cover it with a thin Skin of Varnish, immediately after laying it on; but this is not all, for if you wipe it with a Spunge dipt in clear Water, it will rise from the bottom of the Painting, and peel off like a Water-Colour: This is particularly observable in Moist Weather, and seems to be owing to this, that Verdigris being a kind of Salt, is easily dissolved in moist Air; and especially if soften'd with the additional wetness of a Spunge.