CHAP. 40.—THE VARIOUS KINDS OF MINIUM. THE USE MADE OF
IT IN PAINTING.
According to Juba minium is also a production of Carmania,
1
and Timagenes says that it is found in Æthiopia. But from
neither of those regions is it imported to Rome, nor, indeed,
from hardly any other quarter but Spain ; that of most note
coming from Sisapo,
2 a territory of Bætica, the mine of minium
there forming a part of the revennes of the Roman
people. Indeed there is nothing guarded with a more constant
circumspection; for it is not allowable to reduce and refine
the ore upon the spot, it being brought to Rome in a crude
state and under seal, to the amount of about two thousand
pounds per annum. At Rome, the process of washing is performed,
and, in the sale of it, the price is regulated by statute;
it not being allowed to exceed
3 seventy sesterces per pound.
There are numerous ways, however, of adulterating it, a source
of considerable plunder to the company.
4
For there is, in fact, another kind
5 of minium, found in most
silver-mines as well as lead-mines, and prepared by the calcination
of certain stones that are found mixed with the metallic
vein—not the minerals, however, to the fluid humours of
which we have given
6 the name of quicksilver; for if those are
subjected to the action of fire they will yield silver—but another
kind of stone
7 that is found with them. These barren
8 stones,
too, may be recognized by their uniform leaden colour, and it
is only when in the furnace that they turn red. After being
duly calcined they are pulverized, and thus form a minium of
second-rate quality, known to but very few, and far inferior
to the produce of the native sand that we have mentioned.
9
It is with this substance, then, as also with syricum, that
the genuine minium is adulterated in the manufactories of the
company. How syricum is prepared we shall describe in the
appropriate place.
10 One motive, however, for giving an under-coat
of syricum to minium, is the evident saving of expense
that results therefrom. Minium, too, in another way affords a
very convenient opportunity to painters for pilfering, by wash-
ing their brushes,
11 filled with the colouring matter, every now
and then. The minium of course falls to the bottom, and is
thus so much gained by the thief.
Genuine minium ought to have the brilliant colour of the
kermes berry;
12 but when that of inferior quality is used for
walls, the brightness of it is sure to be tarnished by the
moisture, and this too, although the substance itself is a sort
of metallic mildew. In the mines of Sisapo, the veins are
composed exclusively of the sandy particles of minium, without
the intermixture of any silver whatever; the practice being
to melt it like gold. Minium is assayed by the agency of gold
in a state of incandescence: if it has been adulterated, it will
turn black, but if genuine, it retains its colour. I find it
stated also that minium is adulterated with line; the proper
mode of detecting which, is similarly to employ a sheet of red
hot iron, if there should happen to be no gold at hand.
To objects painted with minium the action of the sun and
moon is highly injurious. The proper method of avoiding
this inconvenience, is to dry the wall, and then to apply, with
a hair brush, hot Punic wax, melted with oil; after which,
the varnish must be heated, with an application of gall-nuts,
burnt to a red heat, till it quite perspires. This done, it must
be smoothed down with rollers
13 made of wax, and then polished
with clean linen cloths, like marble, when made to shine.
Persons employed in the manufactories in preparing minium
protect the face with masks of loose bladder-skin, in order to
avoid inhaling the dust, which is highly pernicious; the covering
being at the same time sufficiently transparent to admit of
being seen through.
Minium is employed also for writing
14 in books; and the
letters made with it being more distinct, even on gold or marble,
it is used for the inscriptions upon tombs.