Thanks for the reply.
I'm now getting very good results with this process.
For these experiments, the etched metal is C-1018 cold rolled steel.
The image used is the same in all cases; 5 lines of text ranging in size from 0.05 to 0.15 inches in height. Total image area < 1sq. in.
The cathode is a piece of 40x40 mesh stainless steel cloth, somewhat larger than the image.
The power source is a lab type power supply, operated in constant current mode. I found out quickly that 25-200 mA was inadaquate. For these experiments 4 Amps was used in all cases. Etching time was 60 sec.
The photopolymer is designed to withstand acids, a mild base (sodium carbonate solution) is used to "develop" it and a stronger solution removes it easily at the end of the process. The photopolymer is "fixed" with a mild acid (white vinegar).
Deep etching is required here, at least 0.010". In actual application the work will be hot blued after etching the image, only etch depth is available to provide contrast.
The results:
10% hydrochloric acid solution; required voltage compliance for 4A was 6V. Probing the etch with a needle under strong light and magnification, it appears to be 10 mils deep or so. No sign of undercutting, image quality is excellent.
Marking Methods, Inc. MSC-4 etchant; the results are indistinguishable from HCL. Required voltage compliance was 6.75V.
Martronics (Etch O Matic) GP Electrolyte; depth of etch was a disappointing 3 mils. no undercutting. Required voltage compliance was 6V.
I intend to also try a sulfuric acid solution, the MSC-4 smells exactly like dilute sulfuric acid.
I will also try a higher current, Maybe I can get to 15 mils etch depth before the image quality suffers. The GP electrolyte will not be used again.
BTW, you can get the black fill in the etching by rubbing in some cold blue after etching. This is one application where cold blue works perfectly.
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