Respecting the preparation of verdigris, various and in part
contradictory opinions have been entertained; and at present, when it
is with certainty known, it appears that the process is almost the
same as that employed in the time of Theophrastus, Dioscorides, and
Vitruvius[462]. At that period, however, every natural green copper
salt was comprehended under the name of _ærugo_. Dioscorides and
Pliny say expressly, that a substance of the nature of those stones
which yielded copper when melted, was scraped off in the mines of
Cyprus; as is still practised in Hungary, where the outer coat of the
copper ore is collected in the like manner, and afterwards purified
by being washed in water. Another species, according to the account
of Dioscorides, was procured from the water of a grotto in the same
island; and the most saleable natural verdigris is still collected
by a similar method in Hungary. The clear water which runs from old
copper-works is put into large vessels, and after some time the green
earth falls to the bottom as a sediment.
The artificial _ærugo_ of the ancients, however, was our verdigris,
or copper converted into a green salt by acetic acid. To discover the
method of procuring this substance could not be difficult, as that
metal contracts a green rust oftener than is wished, when in the least
exposed to acids. The ancients, for this purpose, used either vessels
and plates of copper, or only shavings and filings; and the acid they
employed was either the sourest vinegar, or the sour remains left when
they made wine; such as grapes become sour, or the stalks and skins
after the juice had been pressed from them[463]. Sometimes the copper
was only exposed to the vapour of vinegar in close vessels, so that it
did not come into immediate contact with the acid; in the same manner
as was practised with plates of lead in the time of Theophrastus, when
white-lead was made, and as is still practised at present. Sometimes
the metal was entirely covered with vinegar, or frequently besprinkled
with it, and the green rust was from time to time scraped off; and
sometimes copper filings were pounded with vinegar in a copper mortar,
till they were changed into the wished-for green salt. This article
was frequently adulterated, sometimes with stones, particularly
pumice-stone reduced to powder, and sometimes with copperas. The first
deception was easily discovered; and to detect the second, nothing
was necessary but to roast the verdigris, which betrayed the iron by
becoming red; or to add to the verdigris some gall-nut, the astringent
ingredients of which united with the oxide of iron of the copperas, and
formed a black ink.
In early periods verdigris was used principally for making plasters,
and for other medicinal purposes; but it was employed also as a colour,
and on that account it is by Vitruvius reckoned among the pigments.
When applied to the former purpose, it appears that the copper salt
was mixed with various other salts and ingredients. One mixture of
this kind was called vermicular verdigris[464], the accounts of which
in ancient authors seem to some commentators to be obscure; but in my
opinion we are to understand by them, that the ingredients were pounded
together till the paste they formed assumed the appearance of pieces or
threads like worms; and that from this resemblance they obtained their
name. For the same reason the Italians give the name of _vermicelli_ to
wire-drawn paste of flour used in cookery[465]. When the process for
making this kind of verdigris did not succeed, the workmen frequently
added gum to it, by which the paste was rendered more viscous; but this
mixture is censured both by Pliny and Dioscorides. It appears that the
greater part of the verdigris in ancient times was made in Cyprus,
which was celebrated for its copper-works, and in the island of Rhodes.
At present considerable quantities of verdigris are manufactured at
Montpelier in France, and by processes more advantageous than those
known to the ancients[466]. The dried stalks of grapes are steeped
in strong wine, and with it brought to a sour fermentation. When the
fermentation has ceased, they are put into an earthen pot, in alternate
layers with plates of copper, the surface of which in a few days is
corroded by the acetic acid, and the salt is then scraped off. It is
certain, that, even in the fifteenth century, the making of verdigris
was an old and profitable branch of commerce in France. The city of
Montpelier having been obliged to expend large sums in erecting more
extensive buildings to carry it on, and having had very small profits
for some years before, received by letters patent from Charles VI., in
1411, permission to demand sixteen sous for every hundred weight of
verdigris made there. In later times this trade has decayed very much.
Between the years 1748 and 1755, from nine to ten thousand quintals
were manufactured annually, by which the proprietors had a clear profit
of 50,000 crowns; but a sudden change seems to have taken place, for
in 1759 the quantity manufactured was estimated at only three thousand
quintals. This quantity required 630 quintals of copper, valued at
78,750 livres: the expenses of labour amounted to 1323 livres; the
necessary quantity of wine, 1033 measures, to 46,485 livres, and
extraordinaries to 10,330 livres; so that the three thousand quintals
cost the manufacturers about 136,888 livres. In the year 1759, the
pound of verdigris sold for nine sous six deniers: so that the three
thousand quintals produced 142,500 livres, which gave a net profit of
only 5612 livres. Other nations, who till that period had purchased
at least three-fourths of the French verdigris, made a variety of
experiments in order to discover a method of corroding copper which
might be cheaper; and some have so far succeeded that they can supply
themselves without the French paint in cases of necessity[467].
In commerce there is a kind of this substance known under the name of
distilled verdigris, which is nothing else than verdigris purified,
and crystallized by being again dissolved in vinegar[468]. For a
considerable period this article was manufactured solely by the Dutch,
and affords an additional example of the industry of that people.
Formerly there was only one person at Grenoble acquainted with this
art, which he kept secret and practised alone; but for some years past
manufactories of the same kind have been established in various parts
of Europe.
The German name of verdigris (_Spangrün_) has by most authors been
translated Spanish green; and it has thence been concluded that we
received that paint first from the Spaniards. This word and the
explanation of it are both old; for we find _ærugo_, and _viride
Hispanicum_, translated _Spangrün_, _Spongrün_, or _Spansgrün_,
in many of the earliest dictionaries[469], such as that printed in
1480[470]. For this meaning, however, I know no other proof than the
above etymology, which carries with it very little probability; and
I do not remember that I ever read in any other works that verdigris
first came from the Spaniards.