Processing the Master
Making The Master

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The men who cut masters for our records are apt to be more or less isolated geographically from the Before and After. The recording and editing at one end, the plating and pressing of the actual record at the other; but though they serve as a vital in-between link in the whole procedure, they are closest to the Before, and this merely because the disk recording of a master is no more than a special branch of the recording art, which includes nowadays all kinds of disk and tape recording.

But once the finished lacquer is in its shipping box we enter a new world, a world of more or less mass reproduction, where the object is the making of many from one. It is, you might say, equivalent to the printing plant as compared to the editorial office. If our stenographers could "type" final copy for printing direct on their own machines, then we would have in a newspaper office the equivalent the engineer who cuts the phonographic master. All that remains is the actual technical process of multiple duplication.

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The Printing 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 apt to be housed in the company's plushy front offices! Plating plants are off in far city corners, or housed in strictly business like factory lofts.

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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 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. Onto 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 get rid of the wax and the graphite, leaving a mold of metal.

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 g 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 treatment.

From this point on, the objective is to build up a solid metal backing on the thin silver coat. You may be slightly confused, as I was, since this "backing" is actually being deposited on the front of the original disk. But if you will consider that we are after 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, you will understand that we are looking at the silver actually 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, sometimes nickel, laid down slowly on the silver surface we have just made-fine grained in order not to disturb the tiny groove patterns and to hold them accurately in place. After this, a coarser grained metal can be piled on; in one plant I visited, however, another layer of fine grained "pre-plating" was added first, to be doubly sure. The coarse coating is one much faster, or at the very slow, fine-grain preplating speed it would take perhaps weeks to build a strong up enough layer of metal. One company has 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 systems, using the usual immersion tanks with moving arms to swish the contents about, take a good deal longer at best.

And so enough metal is 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 usually damaged in this separating process and cannot be used again; so the new metal negative is now the only form in which the grooves exist. Being a negative, it has raised "groove" with valleys between.

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Metal-Matrix Negative to Positive "Mother"

This metal negative or metal matrix can be used to stamp out actual positive records in plastic, and occasionally is so used. But since it is the only existing copy now of the original and cannot be replaced when worn out, it is used instead, in most cases, to produce what is called, for obvious reasons, a mother - a positive metal record that can, if you wish, actually be played, and sometimes is, for testing purposes. But playing is not this mother's destined role. (Indeed, the whole business of plating and processing has a strangely fertile aspect. It is a kind of matriarchal arrangement, queen-bee-like, the master fecundating a mother who in turn is to produce multiple metal offspring destined in their turn to produce masses of those worker-like records which give forth, finally, with the endless reproduction of actual sound itself!) Instead, she submits to another plating operation much like the first, ending in another metal negative. Since the mother, unlike the fragile lacquer original, is made of sterner metal and can be "fertilized" time after time, giving birth to negative after negative in metal, all identical with the first, we have in her a source of prolification - multiplied prodigiously when each of her final negative offspring, called stampers, can press out as many as a thousand or so actual plastic records-grandchildren.

But back, briefly, to the plating room and our original metal matrix one-of-a-kind negative, its silver surface just neatly stripped from the lacquer. The first step in preparing for the creation of the mother is, of all things, to remove the silver that now contains the direct groove Impression. (Remember again, the silver was next to the lacquer-it went on first-and is on the bottom of the plating subsequently heaped on top of it. Strip the lacquer away, turn the entire plating over, and you are looking at the other side of the silver, the down-side, that was next to the original lacquer grooves. If you will think of a standard home waffle iron, you can better imagine this process: strip off the waffle and turn it over to show the bottom pattern next to the butter.) The silver is removed because it would quickly oxidize and corrode in the air; it is, however, such an extremely thin coating, molecule-thin, that the underlying harder metal has virtually the same sharp image as the original. A swish or two of chromic acid takes the silver away faster than it was deposited by spray in the first place.

With the silver off but the groove image still nicely metalized in this negative matrix, the whole plating process is repeated to "grow" a new image, the mother. But first, before plating, a separating solution is applied to the surface, so that, though metal will plate on metal, it can be stripped off like a well-buttered waffle later on; otherwise the entire thing would become a useless solid metal block. (Shades of waffles that stick-the separating solution is equivalent to the traditional butter!) And so it goes - fine-grain metal, coarse metal, as before, and at the end, the mother is created. She is the new positive, stripped easily away from the original metal negative.

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Mother to Progeny - Multiple Stampers

I've anticipated the mother's fecundity. The mother herself is given separating solution and then plated in the same old way, the stripping apart producing the first of her progeny, a negative stamper, actually used to press out the final records. The stamper is identical with the negative metal matrix, but is no longer unique. The mother is unharmed; she can be replated again and again, a surprising number of times, before her essential powers are impaired (that is, the record groove image damaged and worn and with), each replating, she gives birth to still another negative stamper.

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Stamping to Pressing

There's a lot to be done to this fourth-generation stamper (positive original; negative metal matrix; positive mother; negative stamper) before the fifth and final generation can be produced in the hiss of super-heated steam. A hard but ultra-thin chrome surface must be plated on, for wear. Then there's the little matter of that hole in the middle-a very crucial business-not to mention the stamper's rear side, which must be shaved to the right thickness to fit the presses, and the outside edge which must be trimmed to size. The rear surface is machined away in a lathe operation that would have most uninitiates fascinated. I was. A precision gouge neatly scrapes a spiral track from the outside of the back right to the inside, shaving off all the irregularities, leaving a mirror-bright flat backside. The edges trimmed, the stamper then goes to the centering machine.

If you are mathematically minded, you may appreciate the problem involved in finding the exact center of a spiral, especially when that spiral is made of wavering, wobbly Lines. Impossible! (Don't be confused by the disk itself-the center of the disk is not what we want.) Of course, the original lacquer had its hole in the exact center. The hole was what determined the original spirals. But unfortunately that hole, spread and stretched in the plating, cannot be relied upon. One must start anew and make a new hole.

How? Simply by trial and error. As we all know, to our pain and distress, the slightest deviation from a perfect center hole is fatal to recorded music of any sort. Yet the man who makes the hole in the record does it just the way you and I might-by playing the grooves with a sort of needle and watching the way the arm wobbles back and forth. He is helped, though, by a magnifying device that reads the arm's motion on a big dial; when the dial's wobbles become reasonably uniform, he bangs down a quick punch that cuts a sudden hole. And frequently, the record having slipped, it is wrong. The first man I saw at this job tried one master five times, and gave up; it was off-center every time in a different direction. Every single record ever made goes through this primitive trial-and-error search for the perfect hole, no better way having been found to do it.

As soon as the master has its hole, it loses it. Another punch knocks out a big disk a couple of inches across from the middle to fit the center of the press. But the disk's position is exactly determined by the small hole, and so the essential information is preserved, the final hole in the record to be made in the actual pressing according to it.

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If you have followed thus far with reasonable clarity of mind, you may have a few questions left, one or two of which I can anticipate, though this account hardly purports to complete coverage in every detail.

Doesn't the groove image lose tremendously in all these generations of plating-copies and copies and copies? No, it does not. With careful plating, fine-textured metal, the contact is so close that the image is accurate within millionths of an inch; the loss from one step to the next is thus very small, though without doubt there is a decay of sorts from the initial clarity.

How about other ways of plating the master lacquer record - the much-mentioned gold-sputtering, for instance? 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 (I understand) so accurate or trustworthy. The gold-sputtering process is more complex, and, according to some advices I've received, 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.

I suspect, quite privately, that much of the appeal of the gold-sputter method is in the name. "Silver-spray" is attractive, but cannot compete with the valuable sound of "gold-sputter" in sheer impressiveness.

Metal shortages? Definitely - and steps are being taken to meet them. Silver, tin, chrome, and the like are used only in relatively tiny quantities, and much can be recycled. But the basic heavyweight plating is done in copper and nickel conventionally, and these are currently difficult to get. One company has worked out a remarkably good substitute in a more common metal (which must be nameless) already in use, which would seem to remove for the time being one of the main threats in the way of a record plating tie-up. Experiment is going on at every stage of the record process in the use of substitutes - or, as they frequently are, improvements and it will take a very serious international disturbance to bring production to a real halt.

Excerps from the Saturday Review Home Book of Recorded Music and Sound Reproduction
by Edward Tatnall Canby

1952 - Prentice - Hall, Inc. New York

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