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For the first several decades of disc record manufacturing, sound was recorded directly on to the master disc (also called the matrix, sometimes just the master) at the recording studio. From about 1950 on (earlier for some large record companies, later for some small ones) it became usual to have the performance first recorded on audio tape, which could then be processed and/or edited, and then dubbed 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. The mastering process was originally something of an art as the operator had to manually allow for the changes in sound which affected how wide the space for the groove needed to be on each rotation. Sometimes the engineer would sign his work, or leave humorous or cryptic comments in the lead-out groove area, where it was normal to scratch or stamp identifying codes to distinguish each master. == Mass producing == The original soft master, known as a "lacquer", was silvered using the same process as the silvering of mirrors. To prepare the master for making copies, soft masters made of wax were coated with fine graphite. Later masters made of lacquer were sprayed with a saponin mix, rinsed, and then sprayed with stannous chloride, which sensitized the surface. After another rinse, they were sprayed with a mix of the silver solution and dextrose reducer to create a silver coating. This coating provided the conductive layer to carry the current for the subsequent electroplating, commonly with a nickel alloy. In the early days of microgroove records (1940–1960), nickel plating was only brief, just an hour or less. This was followed by copper plating, which was both quicker and simpler to manage at that time. Later with advent of nickel sulfamate plating solutions, all matrices were plated with solid nickel. Most factories transferred the master matrix after an initial flash of nickel from a slow warm nickel electroplating bath at around 15 amperes to a hot 130 degree nickel plating bath. In this, the current would be raised at regular intervals until it reached between 110 A and 200 A, depending on the standard of the equipment and the skill of the operators. 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 passifying (see below), the metal master was then electroplated (electroformed) to create metal positive matrices, or "mothers". From these positives, stampers (negatives) 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 from adhering to the mother. There were several methods used; EMI favoured the fairly difficult albumin soaking method whereas CBS Records and Philips used the electrolytic method. Soaking in a dichromate 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 the 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 for the pin on the playback turntable. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Production of gramophone records」の詳細全文を読む スポンサード リンク
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