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164
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DE NATURA FOSSILIUM
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added
to one, pitch to the other. A lump of lime is first quenched in wine
then crushed in a mortar with lard and either the sap of the fig tree
or pitch. That made with pitch is darker and readily distinguished from
the other. According to Pliny when a surface is coated with maltha, oil
is rubbed over it. Metal workers also have a genus of maltha with which
they fill cracks in the bottom of large crucibles so that the molten
metal will not be lost through them. If the crucible is made of ash the
molten metal produces flaws that eventually break it. Fresh maltha will
hold molten metal just as old maltha holds water. The maltha of the
metal workers is made from unslacked lime, ox blood and meal.
Lithocolla differs
in composition and use from the two older malthas. The former is made
from powdered marble and beef glue and is used to cement fragments of
marble or rock to the parent mass. Today two kinds are in use each
containing powdered marble or rock similar to the fragments of marble
or rock that are to be cemented. White of egg is added to one variety,
pitch to another. Some people add other ingredients. Lapidaries have
their own variety that is used to cement rough stones to the dorp. This
is usually made from powdered brick and pitch.
Since I have discussed sand, lime, maltha and lithocolla I
should say something about artificial stones. There are two genera of
these. One is made from stones and lacks a name, the other is made from
earth and is called later (brick). The former can be made from
any stone by simply giving it a new shape although the original color
is lost. Thus one large stone can be made from a number of small ones
and a small stone from several smaller ones as aetites, from
the small pebbles found in a geode and flint from small pieces of
flint. Similarly a whetstone can be made from silicious fragments to
which silver or other materials are added. First the stone is crushed
to a powder in a sandstone or stone mortar and then egg white, linseed
oil and juniper gum is mixed with the powder. The mass can be molded to
any form. If a large amount of egg white is added to the mixture it
dries quickly and if a large amount of gum the rock is harder. Some of
these stones can be colored by adding a pigment although if they are
made with pitch they are always black.
Bricks
are made from earth. They are usually made from whitish marl or red
ocher. Luneburg brick is made from an unctuous aluminous earth. Good
bricks are made from a pumiceous earth at Sandarlik, Asia Minor, and
Calentus and Cartagena, Spain. These will float on water. In olden
times bricks were made from earth to which sand, male sand, had been
added. No matter what variety of earth is used first it is moistened
with water. The bricks are then molded from this mud. They are usually
made in spring and fall so they will dry during one uninterrupted
period. If they are made in summer, according to Vitruvius, they are
usually defective since the sun, when directly overhead, burns so
strongly the bricks shrink and soon have the appearance of being dry
and yet are moist in-
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