Verdigris
3 of the 6 encyclopedias on this shelf carry an entry for Verdigris. All 3 are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
Important: Safety Warning
This page presents medical treatment from an era before modern medicine. The remedies described are ineffective against the conditions named, and some of the ingredients or doses are harmful. Do not use them to treat any illness; consult a qualified medical professional.
This information has been left in for historical purposes but should not be acted upon.
or VERDEGRIS, in chemistry, a green pigment prepared in the the S. of France, by by exposing thin plates of copper for some time to the action of the refuse of the grape from which wine has been made. In the United States it is sometimes prepared by placing copper plates in contact with woolen cloths, which have been soaked in pyroligneous acid. It is soluble in dilute sulphuric acid, and is very poisonous. In pharmacy , verdigris is occasionally used externally , in powder or mixed with honey and vinegar, as an escharotic.
Aiton's Encyclopedia (1910)
ver'di-gres, literally green of copper. It is a coloring substance obtained by exposing plates of copper to air in the presence of acetic acid. It is much used in dyeing wool, in printing calico, in gilding, and in various other arts. Verdigris is a dangerous poison. The best common antidote is white of eggs and milk. The acid of many fruits, if boiled in a copper kettle, combines with copper to form verdigris in sufficient amounts to render the fruit poisonous. Food taking on the slightest tinge of green from cooking in copper should be thrown away. The vinegar of sour pickles corrodes copper and produces verdigris.
The Encyclopedia of Founding (1892)
A very poisonous diacetate of copper, which forms in a green crust on its surface if exposed to a damp atmosphere. It is useful in the arts as a pigment. See COPPER. Vermilion, or mercuric sulphide, occurs native as cinnabar, a dull red mineral, which is the most important ore of mercury; bright red in color; has a good body, and is useful as a pigment for paints. See MERCURY.
What Has Changed in the Last Century
The vineyard method Collier's described in 1921 -- stacking copper plates with grape refuse in the south of France -- has vanished as an industry; copper acetates are now made in controlled chemical plants, and painters long ago abandoned verdigris as a pigment because it darkens and blackens with age, replaced by stable phthalocyanine and chromium greens. Collier's advice that it be used "externally, in powder or mixed with honey and vinegar, as an escharotic" is gone from medicine entirely. Aiton's 1910 kitchen warning was sound in substance but the problem was engineered away: copper pans are now lined with tin or stainless steel, so acidic fruit and pickle vinegar never touch the metal. Modern usage also distinguishes more carefully between true verdigris (copper acetates) and the green patina on roofs and statues, which is mostly basic copper carbonate and sulfate.
Written for this edition, 2026.