Identifier: halftoneprocessp00verf (find matches)
Title: The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass
Year: 1904 (1900s)
Authors: Verfasser, Julius
Subjects: Photoengraving
Publisher: London, Iliffe & sons, limited
Contributing Library: Getty Research Institute
Digitizing Sponsor: Getty Research Institute

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ter; theetcher has little or no control. If the film blisters andleaves the plate the acid is too strong or the exposureof the print too short, or the burning-in not sufficient.If the film crumbles away in powder it has been over-burnt. The tendency of the film to be attacked maybe prevented to some extent by adding to the etchingbath one ounce of chrome alum for one hundred ouncesof bath solution. It is not desirable to give a finishingbath in the case of enamel plates, as the delicatesharpness of the dots is impaired, and the plate assumesquite a different appearance, wanting in the cleanlinesswhich distinguishes the original image. Fine etching,however, may be done as subsequently described. Where the burning-in has been overdone on zincthe etching will immediately show the crystallinestructure into which the zinc has been broken up.There is, indeed, always a granularity in zincetchings which have been prepared by the enamelprocess, owing to the heating of. the plates inburning-in.
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ETCHING THE PLATE, 257 It has been stated that this granular appearancemay be avoided by first immersing in a weak solutionof chromic acid. If now the plate is put in the ordinarynitric acid bath the etching is very rapid. When theyellowish brown precipitate is wiped away the etchedground is seen to be quite smooth. Another way which it is said will secure clean etchingis to add slimy substances such as gum, fish glue,dextrine, etc., to the nitric acid etching bath. Theeffect is to retard the irregular action of the acid. Ifthis mixture is used after the chromic acid bathmentioned above the effect will be to make the etchingsmooth and regular in the hollows. Sulphate of iron has also been suggested as a mordantfor etching zinc, used in a strong solution, but itsaction is slow. Another etching solution for zinc which has a mildand a regular action is the following: Nitric acid, 130parts; water, 100 parts; sal ammoniac, 20 parts;pyroligneous acid (wood vinegar), 20 parts. The con-stitue

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