PROCESSING THE MASTER
THE PLATING PLANT
Making a metal stamper that will actually mold records from hot shellac or
plastic is essentially a multiple plating process - depositing metal upon
metal in the traditional manner, by means of an electric current that
transfers metal through a plating solution directly to the surface being
plated. At this point record making is surrounded by tanks. Rows and rows
of containers filled with poisonous-looking green and yellow and orange
liquids, some steaming, some sloshing about, as objects are swished through
the depths - this is the necessary scene, and by its very nature it is not
likely to be housed in the company's plush front offices! Plating plants
are off in far city corners, or housed in strictly industrial park areas.
PLATING THE LACQUER MASTER
If we are to make an actual metal impression of the lacquer record; we must
either flow on a metal and let it harden, or plate it on cold. The first
process obviously being impossible (lacquer is a soft, highly inflammable
plastic!), some form of plating is the only answer. But how to plate metal onto a non-metal?
Strangely, it's easy, and a number of methods have been used. The oldest,
when master records were cut into wax blocks, was to apply an extremely
thin coating of graphite, a form of carbon that we know as pencil lead,
which conducts electricity. To this coating, thin enough not to disturb
the record groove shape unduly, one could actually plate metal, which would take on the shape of the record grooves. When enough metal had been backed up on the plating, it was an easy matter to strip it from the wax and the graphite, leaving a mold of metal.
Three ways are used to get the first microscopic layer of metal onto the
lacquer. Silver spray is the newest and trickiest. Still used, also, is
the silver pan bath, similar in its chemistry; it takes longer, and is not as accurate or trustworthy. The gold-sputtering process is more complex, but not necessarily better than the silver-spray, and possibly less uniform. The silver methods are more widely used. In the intriguing gold process, the master is mounted in a vacuum chamber between a gold cathode and an anode. A 3000-volt direct current creates a glow discharge, as in a vacuum tube; molecules of gold are deposited on the lacquer by secondary emission, leaving an extremely thin layer similar to the silver layer in the other process. Upon this molecule-thin layer of gold, the usual plating is done.
Lacquers are treated in more ingenious ways, to give metal coatings at first only a molecule or so thick. The most dazzling to watch involves silver nitrate and a simple spray gun. The lacquer surface is "sensitized" by being dipped into a solution of stannous chloride which is washed off in a water spray, leaving a very minute coating. Silver nitrate solution is sprayed at the disk-and, lo, the dead black grows into a perfect mirror of silver in a few seconds. Silver has been deposited in an extremely thin layer by chemical (replacement) action, the stannous chloride acting as a
catalyst to promote the process. The newly silvered disk is washed
(washing is almost a fetish in plating plants) and moves on to its next
From this point on, the objective is to build up a solid metal backing on
the thin silver coat. This may be confusing, since this "backing" is
actually being deposited on the front of the original disk. Remember, that we are making a negative mold, its surface now of silver, in direct contact with the lacquer surface and facing away from us as we look at the record. We are really looking at the silver from the rear, and we are about to add more metal to that rear in order to stiffen it. The original record will eventually be stripped away, leaving the other side of the silver, the facing-down side, as our mold.
The beginning of the build-up of this metal backing support, a layer of very fine-grained and delicate copper or sometimes nickel, is laid down slowly on the silver surface we have just made. It is fine-grained in order not to disturb the tiny groove patterns and to hold them accurately in place. After this, a more coarse grained metal can be piled on, although in some plants, another layer of fine grained "pre-plating" was added first, to be doubly sure. The coarse coating is desirably much faster, since at the slow fine-grain pre plating speed, it would take perhaps weeks to build up a strong enough layer of metal. One company used special rotating disk anodes that swish around close to the surface of the metal record and do the plating job to required thickness in a few hours. Other much slower systems use the usual immersion tanks with moving arms to swish the contents about.
Enough metal is thus put on the back of the silver surface to support it
rigidly. Whereupon, with a quick blow of a special hammer and perhaps a
wiggle or two of an inserting tool, the entire silver-copper mold breaks
free from the lacquer, and we have a negative in metal, the back side or
down-surface of the silver a mirror-image the original grooves. The
lacquer is usually damaged in this separating process and cannot be used
again; so the new metal negative, or "matrix", is now the only form in
which the grooves exist. Being a negative, the grooves become sharp ridges with flat valleys between.