more at http://electronics.quickfound.net/ Making phonograph records, from wax masters to shellac 78s. Narrated by Milton Cross, author of "Milton Cross' Encyclopedia of the Great Composers and Their Music." Public domain film from the Library of Congress Prelinger Archive, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization. http://en.wikipedia.org/wiki/Production_of_gramophone_records For the first several decades of disc record manufacturing, sound was recorded directly on to the master disc .. A record cutter would engrave the grooves into the master disc. Early versions of these master discs were soft wax, and later a harder lacquer was used... Mass producing The soft master known as a lacquer would then be silvered using the same process as the silvering of mirrors... This silver coating provided the conductive layer to carry the current for the subsequent nickel plating electroplated with a metal, commonly a nickel alloy... Most factories transferred the Master Matrix after an initial flash of Nickel in a slow warm nickel electroplating bath... This and all subsequent metal copies were known as matrices. When this metal master was removed from the lacquer (master), it would be a negative master or Master Matrix, since it was a negative copy of the lacquer. (In the UK, this was called the master; note the difference from soft master/lacquer disc above). In the earliest days the negative master was used as a mold to press records sold to the public, but as demand for mass production of records grew, another step was added to the process. After removing the silver deposit and passifing, the metal master was then electroplated (electroformed) to create metal positive matrices, or "mothers". From these positives, stampers (negative) would be formed. Producing mothers was similar to electroforming Masters, except the time allowed to turn-up to full current was much shorter and the heavier Mothers could be produced in as little as one hour and stampers (145 grams) could be made in 45 minutes. Prior to plating either the Nickel Master or Nickel Mother it needed to be passified to prevent the next matrix adhering to the previous matrix. There were several methods used, EMI favoured the fairly difficult Albumin soaking method where as CBS Records and Phillips used the Electrolytic method. Soaking in a di-chromate solution was another popular method, however this method risked contaminating the Nickel solution with chrome. The electrolytic method was similar to the standard electrolytic cleaning method except the cycles were reversed finishing the process with Matrix as the anode. This also cleaned the surface of the matrix about to be copied. After separating from the Master a new mother was polished with a fine abrasive to remove or at least round-off the microscopic "horns" at the top of the grooves, produced by the cutting lathe. This allowed the vinyl to flow better in the pressing stage and reduced the non-fill problem. Stampers produced from the mothers after separating were chrome plated to provide a hard stain-free surface. Each stamper was next centre punched, methods used included aligning the final locked groove over three pins or tapping the edge while rotating under the punch until the grooves could be seen (through a microscope) to move constantly towards the centre. Either method was quite skilled and took much effort to learn. The centre punch not only punched a hole but formed a lip which would be used to secure the stamper into the press. The stamper was next trimmed to size and the back sanded smooth to ensure a smooth finish to the mouldings and improve contact between the stamper and the press die. The edge was then pressed hydraulically to form another lip to clamp the edge down on the press. The stampers would be used in hydraulic presses to mould the LP discs. The advantages of this system over the earlier more direct system included ability to make a large number of records quickly by using multiple stampers. Also, more records could be produced from each master since stampers would eventually get damaged but rarely wear out. Since the master was the unique source of the positive, made to produce the stampers, it was considered a library item. Accordingly, copy positives, required to replace worn positives, were made from unused early stampers. These were known as copy shells and were the physical equivalent of the first positive. The "pedigree" of any record can be traced through the positive/stamper identities used, by reading the lettering found on the record run-out area...

• published: 23 Dec 2011
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