CHAP. 20.—THE DIFFERENT KINDS OF COPPER AND ITS COMBINATIONS.
PYROPUS. CAMPANIAN COPPER.
We will now return to the different kinds of copper, and its
several combinations. In Cyprian copper we have the kind
known as "coronarium,"
1 and that called "regulare,"
2 both
of them ductile. The former is made into thin leaves, and,
after being coloured with ox-gall,
3 is used for what has all
the appearance of gilding on the coronets worn upon the stage.
The same substance, if mixed with gold, in the proportion of
six scruples of gold to the ounce, and reduced into thin plates,
acquires a fiery red colour, and is termed "pyropus."
4 In
other mines again, they prepare the kind known as "regulare,"
as also that which is called "caldarium."
5 These differ from
each other in this respect, that, in the latter, the metal is only
fused, and breaks when struck with the hammer, whereas the
"regulare" is malleable, or ductile,
6 as some call it, a property
which belongs naturally to all the copper of Cyprus. In the
case, however, of all the other mines, this difference between
bar copper and cast brass is produced by artificial means. All
the ores, in fact, will produce bar or malleable copper when
sufficiently melted and purified by heat. Among the other
kinds of copper, the palm of excellence is awarded to that of
Campania,
7 which is the most esteemed for vessels and utensils.
This last is prepared several ways. At Capua it is melted
upon fires made with wood, and not coals, after which it
is sprinkled with cold water and cleansed through a sieve
made of oak. After being thus smelted a number of times,
Spanish silver-lead is added to it, in the proportion of ten
pounds of lead to one hundred pounds of copper; a method
by which it is rendered pliable, and made to assume that agreeable
colour which is imparted to other kinds of copper by the
application of oil and the action of the sun. Many parts,
however, of Italy, and the provinces, produce a similar kind
of metal; but there they add only eight pounds of lead, and,
in consequence of the scarcity of wood, melt it several times
over upon coals. It is in Gaul more particularly, where the
ore is melted between red-hot stones, that the difference is to
be seen that is produced by these variations in the method of
smelting. Indeed, this last method scorches the metal, and
renders it black and friable. Besides, they only melt it twice;
whereas, the oftener this operation is repeated, the better in
quality it becomes.
(9.) It is also as well to remark that all copper fuses best
when the weather is intensely cold. The proper combination
for making statues and tablets is as follows: the ore is first
melted; after which there is added to the molten metal one
third part of second-hand
8 copper, or in other words, copper
that has been in use and bought up for the purpose. For it
is a peculiarity of this metal that when it has been some time
in use, and has been subject to long-continued friction, it becomes
seasoned, and subdued, as it were, to a high polish.
Twelve pounds and a half of silver-lead are then added to
every hundred pounds of the fused metal. There is also a
combination of copper, of a most delicate nature, "mould-copper,"
9
as it is called; there being added to the metal one
tenth part of lead
10 and one twentieth of silver-lead, this
combination being the best adapted for taking the colour
known as "Græcanicus."
11 The last kind is that known as
"ollaria,"
12 from the vessels that are made of it: in this
combination three or four pounds of silver-lead
13 are added to
every hundred pounds of copper. By the addition of lead to
Cyprian copper, the purple tint is produced that we see upon
the drapery of statues.