Electrotyping

Electrotyping is an application of the art of electroplating to typography, used for making duplicate plates for relief printing (letterpress). In copying engraved plates for printing purposes, copper may be deposited upon the original plate, the surface of which is first rendered slightly dirty, by means of a weak solution of wax in turpentine or otherwise, to prevent adhesion. The reversed plate thus produced is then stripped from the first and used as cathode in its turn, with the result that even the finest lines of the original are faithfully reproduced. The electrolyte commonly contains about 1.5 lb (0.68 kg) of copper sulfate and 2 lb (0.91 kg) of strong sulfuric acid per gallon, and is worked with a current density of about 10 amperes per sq. ft., which should give a thickness of 0.000563 in. of copper per hour.

Moulds for reproducing plates or art-work are often taken in plaster, beeswax mixed with Venice turpentine, fusible metal, or gutta-percha, and the surface being rendered conductive by powdered graphite, copper is deposited upon it evenly throughout. For statuary, and "undercut" work generally, an elastic mould of glue and treacle (80:20 parts) may be used; the mould, when set, is waterproofed by immersion in a solution of potassium bichromate followed by exposure to sunlight, or in some other way. The best results, however, are obtained by taking a wax cast from the elastic mould, and then from this a plaster mould, which may be waterproofed with wax, black-leaded, and used as cathode. In art-work of this nature the principal points to be looked to in depositing are the electrical connections to the cathode, the shape of the anode (to secure uniformity of deposition), the circulation of the electrolyte, and, in some cases, the means for escape of anode oxygen. Silver electrotyping is occasionally resorted to for special purposes.

History

The process was first used in 1838 by Moritz von Jacobi, a German working in St. Petersburg, Russia at the time of his announcement. C.J. Jordan and Thomas Spencer, both of England, and American Joseph Alexander Adams repeated the process a year later.

References

• This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.

Electrotyping.

Electrotyping was the higher quality way of making duplicate printing plates to Stereotyping. “Electros” as they were commonly called, lasted quite a bit longer than “Stereos” in the printing process. The processes of Electrotyping and Stereotyping were to produce multiple copies of the original printing plate, which were usually made in the form of a zinc or magnesium original, or of a type form. Other forms of original printing plate could be older woodcuts etc. and also newer ones made from different forms of plastic. There were three main ways to produce an Electrotyping mould from the originals. 1. Firstly, there was the more ancient but still high quality wax moulding procedure. This method necessitated the use of a solid backing such as a ¼ inch lead or plastic base onto which liquid paraffin wax had been poured to produce a reasonable thickness of solid wax coating when cooled, sufficient to be able to reproduce the depth required in a final printing plate. The initial making of this liquid wax required an amount of powdered graphite to be mixed into it, to help with the eventual “release” of the wax mould from the original printing plate, usually a type form. To prepare the flat mould prior to impression, an amount of graphite powder was brushed onto the surface of the wax and polished to a sheen, to again aid the removal of the wax mould from the original. Normally, the wax mould process was only used on type forms and not on “half tone” picture blocks or other areas which might form a “lock” to the wax. This may have resulted in the “sticking” of the wax and destruction of part of the mould. Prior to impression, the type face was brushed with graphite as well and the wax plate was lowered carefully onto the type face. These were then slid in between the platens of a hydraulic press and a hand pump was used to apply a light pressure. No heat was used in the process and much skill was required to know just how much pressure was needed for a good result. The pressure was released and the mould and type form were slid out and the mould was carefully hand levered from the type. Usually, certain of the blank areas had to be built up so that in the eventual printing plate these would not be any where near the height of the typeface. Using a conically shaped iron which had been heated over a gas flame; bars of previously prepared wax were held against its side producing a liquid wax at the point of the cone which was then deposited onto the appropriate areas of the mould. A heated copper connection with electrical wire attached was pressed into the wax, near to but outside of the printing area, to provide for the current to produce a copper plate. The mould was again brushed with graphite powder and presented to the electroplating section. Copper does not electroplate onto wax so a small amount of the copper plating solution was poured onto the mould and fine iron filings was sprinkled into it and brushed carefully around. This produced a chemical reaction, as iron mixed with copper sulphate produces metallic copper. The result being that a very thin coat of copper was on the face of the wax mould which could then be inserted into the copper plating bath and a small initial current applied to add to the copper already there. As the copper became thicker, after about 10 minutes then the current was increased. With approximately another dozen moulds in the solution, they were usually left to plate overnight at about 50 amps at 6 volts. Next morning hot water was poured over the copper to release it from the underlying wax and a thin (0.040”) copper shell resulted. This was the “face” of a new printing plate which had to be “backed up” with a lead alloy to produce a printing plate of required thickness for printing. 2. The second method of producing an electrotype was to utilize thin lead sheeting. The preparation of the lead necessitated brushing vigorously with a bronze brush the surface of the lead to scour and eliminate the oxide to produce a bright shine to the lead. This was immediately covered with graphite which was brushed onto the surface to slow the process of oxidation and to also present a release agent to the lead. Lead was not used in the production of moulds from type forms as the amount of pressure required to produce an image in the lead would have destroyed the type. Lead was mainly used on zinc and magnesium plates. The original plates were placed on a steel tray which fitted the hydraulic press and “bearers” of the same thickness as the printing plate were place squarely around the plate with packing pieces of zinc placed in the blank areas between. The lead sheet, cut to size, was carefully placed over these plates, face down and a thick wad of newspapers (3/4”) was placed on the lead. The whole assembly was slid into the hydraulic press and the pressure was applied using the motor. Fifty tons may have been required for an area of say 9”x9”. Sometimes a small amount of heat was used in the hydraulic press to help soften the lead. Several impressions may have been required after withdrawing and looking at the back of the lead impression to determine whether there had been sufficient pressure to make a suitable lead mould. Sometimes, at the discretion of the operator small pieces of paper such as blotting paper may have been added to certain areas on the back of the lead to provide a greater pressure to that particular area, particularly on “half tone” or large flat areas. The lead mould was then separated from the original etc. An electrical strap made of lead about an inch wide was soldered to the lead mould and placed on a lead plating tray as before. Hot wax was then painted on the tray and along the side of the lead mould to hold it in place for plating with copper. A special release liquid was applied to the face of the mould prior to plating. The next morning the lead was stripped from the copper shell and the lead discarded. 3. The third method of producing a mould was to use thin (about 0.020”) PVC sheeting. The sheet was cut to size, cleaned with metho and placed on zinc or magnesium “originals”; a sheet of grease proof paper, then a wad of newspapers were laid on top and slid into a hot (315 deg F) hydraulic press, with about a minute’s pause to allow the tray and printing plate to heat, then pressure was applied. To produce a plastic mould, commonly called a “vinyl mould” from a type form, firstly the type was slid into a heated hydraulic press and allowed to heat for about 5 minutes before applying the PVC, grease proof paper and wad of newspapers. Only a small amount of pressure was applied, normally by hand as type faces could be so easily damaged or squashed. An electrical connection of a thin sheet of copper about one inch wide was heated and pressed into the plastic on one of its edges. This plastic mould was then placed in a spraying booth where a double nozzled gun was used to spray silver onto the plastic. Two containers were used to supply the gun; one being a mixture of silver nitrate and ammonia and the other containing a reagent such that when the droplets met in the air adjacent to the surface of the plastic mould, the result would be that the face of the mould would be coated with a very thin cream coloured coat of metallic silver. The finished mould was then laid on a tray ready for plating, similar to the lead moulds. Great caution would be used when first applying the current in the copper plating bath so as to not “burn” the silver nor copper coating around the area of the connection. The current was re-directed through coils to act as resistors thus reducing the current until a sufficient amount of copper had been deposited, especially near the connection to the mould. After plating overnight the vinyl was peeled away from the copper shell. The vinyl mould could be re-sprayed and plated to again produce another copper shell.

Backing Up.

As mentioned earlier, the “face” of a new printing plate had to be “backed up” with a lead alloy to produce a printing plate of required thickness for printing. The back of each copper shell was coated with a liquid flux and the face was coated with a chalk like substance to prevent the backing metal from adhering to it. These copper shells were placed face down in a square tray which was moved via a small hand block and tackle from its normal cooling place and positioned to float on the square molten metal pot containing a lead alloy. By doing this the copper shells in the high sided tray eventually changed colour showing that the flux had been heated sufficiently. The tray was immediately removed from the heat and by using a ladle, molten metal was scooped out of the melting pot and poured carefully onto the back of the copper shells firstly, then allowed to spill over and eventually cover the entire surface of the tray to a depth greater than that which would be required to produce the final thickness of a printing plate. When cooled and solid, by blown air, the large “back up” was tipped out of its tray and the individual printing plates were cut out on a circular saw bench. The edges of the unfinished printing plates were cleaned up using a “bowler” with a rotating blade and random metal castings were prised off. The whole “plate” then cleaned with petroleum. Due to the processes of heating, cooling and contorting of the plates, the printing surface never really ended up perfectly flat. A hammer and punches of various sizes were now used on the back of the plate as the plate was placed face down on a “stone”. This stone was a large and heavy piece of steel, machined flat. To determine where to hit a punch on the back to produce a raising of the surface on the face in the right place, the printing plate was moved slowly over a single gas flame which had no air supplied to it. It thus produced a black smoke on the surface of the copper which when rubbed carefully with a flat rubber (about 1 ½” square) showed highs and lows very effectively. A pair of long marking tongs was then used to mark the back of the plate by following the dark smoked parts on the front. It was then a matter of hitting the right sized punch judiciously on the back of the printing plate to bring the surface up to the right place. Quite often, the face had to be treated by rubbing with a “snakestone” and finishing with a block of charcoal and water. The final thickness (12 point or 0.166” or 10 point or 0.138”) of the printing plate was achieved on a machine with a reciprocating arm and blade called a “rougher”, or conversely on shaving machine. The next process was to route out the waste areas of the plate. The router consisted of a flat bed at about chest height with a bar running along in front of your chest on which another steel arm was positioned to run almost at 90 deg to the first, such that this bar being cantilevered at the back could move a routing head to any position on the bed via hand movements. This was a free hand router. Another type of router was the straight line type which required a little skill to turn the two handles to make it route in the right direction without bumping into a printing area. The waste areas were cut off on the circular saw bench and “bowled” up on the edge. The plate was now ready to be tacked onto laminated timber which will result in a final thickness of “type high” which was 0.918 inch.