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BOOK IX
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197
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spatula
until the entire mass is converted to verdigris. Pliny writes that some
prefer to make it by triturating copper filings and vinegar in a
copper mortar. Thus the verdigris used today is made in many ways.
This is sometimes called viride aeris because of its color.
The
porous verdigris is made in the following manner. One-fourth pint of
strong white vinegar is poured into a copper mortar, preferably one
made from Cyprian copper, and stirred with a copper pestle until it
becomes sticky. Then one-half ounce of spheroidal alum and natural
salt or the whitest and most compact marine salt is added; if salt is
not available use a similar quantity of soda. Then, having been warmed
in the sun, the mass is rubbed in the mortar until it turns green and
becomes sticky from coagulation. Then, having set into a porous mass,
it is laid aside. Material of good color can be made very easily by
mixing one part of vinegar with two parts of old urine and using this
mixture instead of vinegar. If Cyprian copper is not available the best
copper obtainable should be used.
The
third variety of artificial verdigris is used by goldsmiths to solder
gold, as Dioscorides believed. It is prepared in a mortar of Cyprian
copper into which has been poured the urine of a boy. This is stirred
around with a pestle made from the same copper. Pliny has described
this material under the name chrysocolla and mentioned many
methods by which it is prepared. It is worth while to consider his
descriptions. Goldsmiths have appropriated this material for soldering
gold and all others who use it call it by this same name. The best is
made from Cyprian copper and the urine of young boys to which soda is
added. If it is made in a Cyprian copper mortar and rubbed with a
pestle of similar material we call it santerna. When soldering argentiferous gold if a little santerna is
added it makes it brighter. Cupriferous alloys are dulled and soldered
with difficulty. They can be soldered however when one part of gold and
seven parts of silver are added. Today goldsmiths use a substitute they
call borax (borax) more often than chrysocolla. This is made from soda, as I have said in Book III, and contains no verdigris.
Caeruleum is
also produced in different ways although the finest is prepared in the
following manner. Three pounds of very strong vinegar is poured into an
oak vesssel together with a pound of powdered artificial sal ammoniac.
The latter is dissolved and a small staff fastened upright in the
center of the vessel. From this staff sheets of silver full of small
slits are suspended so that they do not touch the vinegar solution.
Before suspending them the slits are first smeared with quicksilver.
The vessel is covered with a lid and sealed so that there are no air
holes. It is then covered with dung or placed in a trench and covered
with earth. After twenty days the vessel is opened and the material
that has collected like rust on the silver sheets is scraped off and
the vessel is again covered and left for twenty days. This procedure is
followed until the silver is entirely eaten away and then new sheets
are suspended in the vessel. The material
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