APPENDIX A : ELECTRO-ETCHING (1855)

Extract from: WALKER, Charles V., Electrotype Manipulation : Part II.

Containing The Theory, and Plain Instructions in the Arts of Electro-Plating, Electro-Gilding, and Electro-Etching; with an account of the Mode of Depositing Metallic Oxides, and of the Several Applications of Electrotype in the Arts.

Nineteenth Edition, London, Published by George Knight and Sons, Manufacturers of Chemical Apparatus and Philosophical Instruments, Foster Lane, Cheapside. 1855.

Page 44. Para.149 "ELECTRO-ETCHING.- The results hither to treated on, have been (....) all obtained at the negative metal : but there is a class of results of no inconsiderable importance to be obtained at the other terminal. The plates of copper, in the decomposition cell, in connection with the copper of the battery, have been described as combining gradually with the oxygen released there, and being eventually consumed; so likewise the plates of silver or gold, which occupy the same relative position, are in a similar manner consumed. But as the varnish placed on moulds, effectively shields the parts protected by it, from the effects of electrolytic action, so also may the copper plates, or the plates of any metal connected with the positive end of the battery, be protected, and the destructive action localised at pleasure.

150. If, for instance, plates of copper be covered on any part of their surface with a stratum of varnish, that part will be excluded from the line of action, while all else is being consumed. Advantage has been taken of this, by coating plates with proper composition and then tracing through it any design, of which an etching is required. The plate in this condition is submitted to the action of the nascent oxygen, and the surface is readily and effectively etched. There is some superiority too possessed by this method, over the ordinary etching by the use of nitric acid; for the operation can be conducted with considerable regularity; it can be rendered a slow or a speedy process; and the result can be taken out from time to time, to be examined, and can be resubmitted in a moment, In fact, of so much importance has this mode of etching been deemed, that it is already one amongst the many applications of this principle for which a patent has been obtained.

151. Process of electro-etching.- Take a burnished copper plate, and solder to it a stout wire; heat the plate, and rub its surface with etching ground, wrapped in silk : be careful to obtain an even coating; then smoke the covered surface over the flame of a candle. Varnish the back of the plate as well as the wire with shell-lac. Trace the design through the etching ground with a fine point. This done, place it in a decomposition cell, and connect it with the copper of a Daniell's or other cell, placing opposite to it a plate of somewhat similar size; after the lapse of ten minutes, remove it, and "stop out" the fine parts with Brunswick black; return it to the decomposition cell for a second ten minutes; and again stop the half tints; again submit it to action for ten minutes, and the operation is complete. Remove the etching ground by means of heat, and a perfect engraving will be found on the plate. The exact duration of the several operations, as well as their number, must be regulated according to circumstances. Electro-etching is an interesting experiment for the lecture table. At the commencement of a lecture, I have submitted a plate to electric action, and before the hour has expired, have distributed proof impressions..."

Comments on text: In an introductory part of the text, Walker describes a 'decomposition cell' as a vessel in which the electrolytic action upon the plates takes place, connected to a Galvanic cell or a battery. A Daniell's cell is a source of Galvanic or Voltaic Electricity, and consists of a copper and a zinc plate in a vessel containing an acidic solution, and devices for maintaining the concentration and acidity of the solution. The etching time of a total of 30 minutes, indicated in para. 151, assuming he is talking about a small demonstration plate, would indicate a voltage of about 1 volt, the output of a single Daniell's cell. The 'copper' of the battery is the side which produces the 'positive' current.

The words "rendered a slow or a speedy process" indicate that the voltage could be low or high, regulated by a different number of cells in series. In another part of the text, a very low voltage is recommended for certain purposes, and the time required for electrotyping, of a week or more, also indicates the use of a low voltage and amperage. Later in the text there is a section on "Electro-tint or Galvanography", (para 173) which is described as a "another form of deposite" produced by painting on 'white metal' with thick etching ground or varnish to create a textured relief, then the whole is ''plumbagoed', that is, covered with graphite, and then a tonal plate is created by the electrotyping or galvanoplastic process.

It was in this sense that Paul Pretsch called his process "photo-galvanography", patented in 1854. This is described in great detail in Charles V Walker's "Electrotype Manipulation, Part I, being the Theory, and Plain Instructions in the Art of Working in Metals, by Precipitating them from their Solutions, through the Agency of Galvanic or Voltaic Electricity" 29th Edition, George Knight and Sons, London. 1859.

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