The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1918-05-02
LEAD AND ZINC PAINTS
H0WP|GMENTSARE MADE
INTERESTING PROCESS USES
MUCH OF PRODUCT OF
OUR MINES.


Ponds in large measure the excellence
of the finished product, says Du Pont
Magazine.
Paints are mixtures of solid par
ticles or pigments and a liquid or
vehicle. Pigments are finely ground
metallic. earthly or animal substances
which give to paint body, hiding and
covering qualities, and color The We
hicle Is a liquid in which the pigment
particles are held in suspension. with
the object of producing a durable
paint film, uniform in color and con-
sistency.
In making good paint many diff
ferent pigments are used, and 1t is
only by their most careful selection
and mixing that the best results can
be obtained. One pigment may have
good covering qualities but lack dur
ability. Another may be much more
durable but lack the necessary hid
ing qualities. Still third may have
the property of neutralizing elements
In the paint film that would otherwise
impair its stability or shorten its life.
The very highest order Of skill on the
part of the paintmaker Is required in
order to select and combine those pig
ments best adapted for the purpose.
The Oldest and most frequently used
pigment Is white lead which was used
as paint material before the Christ
ian era. The Romans called 1t Ger
use" and made it by exposing lead
over sharp vinegar, which differs only
slightly from the modern practice.
Progress has been chiefly in the dir
ection' Of great fineness, higher purity,
and more efficient methods of hand
ling.
The metallic lead from which white
lead Is made occurs in nature as an
ore which must of course be mined
and refined before 1t can be made into
pigment The ores OF lead occur In
veins and pockets far under the sur
face of the ground They are asso =
-ciated with other minerals which must
first be removed, The lead is then
cast into bars or pigs and Is ready
to be made into the white lead OF
commerce,
The Dutch are credited with being
the originators of the process by
which most white lead Is made and
which Is called after them-the Dutch
process. In this process the lead Is
first melted and cast into buckles,
so called because of their fanced re.
colonial times. but which look much
more like the round waffles of the
present day. These buckles are ther
placed in earthen jars over small
quantity of weak acetic acid-whicf
IL practically our domestic vinegar
The pots filled with buckles, are ther
piled twenty or thirty feet high IL
huge sheds In what are known as
"corroding stack" which is as big as
house, Is built up of alternate layers
of corroding pots and spent tan bark
which is nothing more than oak bark
that has been used in tanneries.
In the corroding stacks, which are
closed tight except for small openings
for ventilation, the tan bark begins tc
slowly decompose and give off carbon
dioxide gas, which is the same thing
that our lungs give off when we
breathe In fermenting, the tan bark
acetic acid until it forms vapor. The
vapor rises up through the lead
buckles and gradually turns them
white, for acetic acid has the power
of corroding lead 1t is the nature OF
lead to turn white when 1t corrodes
just as iron turns red and copper
green. The white substance is lead
acetate.
But that Is only half the story, As
fast as the lead is corroded the car
bon dioxide which is constantly being
given off by the fermenting tan bark
attacks 1t. A chemical change takes
place and converts the lead acetate
into basic lead carbonate, or, as we
cess so briefly described takes from
three to four months. The stacks are
then torn down and the particles OF
white lead ground in linseed oil. The
resulting product is the finished pig
ment-the white lead in oil OF COM
merce
The Carter. or. as II is sometimes
called, the quick process. is also in
common use for making white lead
Here the change from lead to white
lead takes place in fifteen days, SO
that there is a decided saving in time
over the Dutch process. In this pro-
cess, the lead. instead Of being piled
In stacks, is powdered from the molten
condition and placed in large closed
wooden cylinders which revolve slow
ly. while they revolve, acetic acid
and carbon dioxide are introduced in
to the cylinders and corrode the lead.
converting II into lead carbonate in
much the same way as in the Dutch
process.
White lead, the most commonly
used of all paint pigments, has the
greatest covering power of any OF the
white pigments. That made by the
Dutch process has unusual hiding
v~x1