Salt Water Etching

I wonder if anyone knows why this is happening. My son and I set up a salt water etching bath with a couple of batteries, a piece of copper and a piece of silver which I had coated with stop out varnish and then scratched a design on. Within seconds the stop out varnish was stripped off the silver! I had tried the same thing with a sharpie and it had started to etch almost straight away - the only problem we had was that we forgot to clean the copper, so the water was too murky to see through. I thought the stop out varnish was supposed to be the stuff to use and you had to use something like white spirit to clean it off. Apparently not the case! Any ideas?

First off, I'd suggest that salt water etching of silver is a pest - it forms silver chloride, which is insoluble in water so will bung up the etched area. Far better to use something that produces a water-soluble salt, like silver nitrate (but keep it in the dark...).

Without knowing which stop-out varnish you're using it's difficult to be certain, but too much current will generate a lot of heat which can lift a number of varnishes (like the shellac-based ones). The traditional ground is bitumen-based, which is more resilient than shellac (but also a lot messier to use and clean up).

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Originally Posted by ps_bond

First off, I'd suggest that salt water etching of silver is a pest - it forms silver chloride, which is insoluble in water so will bung up the etched area. Far better to use something that produces a water-soluble salt, like silver nitrate (but keep it in the dark...).

Without knowing which stop-out varnish you're using it's difficult to be certain, but too much current will generate a lot of heat which can lift a number of varnishes (like the shellac-based ones). The traditional ground is bitumen-based, which is more resilient than shellac (but also a lot messier to use and clean up).

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It was Roberson Stop-out Varnish. Came off in seconds! Maybe the current was just too strong and fast for it. The pen left an imprint very quickly, which is handy if I don't want too deep an etch. I was trying not to have too many chemicals involved, as it will be a pain getting rid of them later. My local council don't allow the disposal of chemical waste and I won't have the amounts to justify paying a private company to do that.

The secret is to clean the surface to be etched as well as possible, until water can coat it without forming small droplets.
The current needed will will vary according to size, but the lower and slower the longer will the resist hold. Once there is a hint of it peeling stop.
You can also use laser printed PnP transfers for your stop out. Dennis.

I'd guess at current given that too - did you key the surface to clean it before painting the stop-out on? I've just been using some Rustins Black Shellac for stop-out with nitric acid; painted on quite thick, but no issues unless I let the etch go on too long (20 mins max).

On the silver nitrate, a) wart pencil (!) and b) it should last for ages. It isn't a great chemical to have around in any quantity (toxic & corrosive), but you can get the silver back by precipitating out silver chloride by adding an excess of common salt, then filter & dry. However... It's worth mentioning that pretty much every chemical used in jewellery is toxic (LD50) - and even so-called "safe" pickles cease to be safe once there is copper dissolved in them.

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Originally Posted by ps_bond

I'd guess at current given that too - did you key the surface to clean it before painting the stop-out on? I've just been using some Rustins Black Shellac for stop-out with nitric acid; painted on quite thick, but no issues unless I let the etch go on too long (20 mins max).

On the silver nitrate, a) wart pencil (!) and b) it should last for ages. It isn't a great chemical to have around in any quantity (toxic & corrosive), but you can get the silver back by precipitating out silver chloride by adding an excess of common salt, then filter & dry. However... It's worth mentioning that pretty much every chemical used in jewellery is toxic (LD50) - and even so-called "safe" pickles cease to be safe once there is copper dissolved in them.

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A wart pencil??? Never heard of that one. Anyway, I think the current has been too strong and perhaps the stop out was not thick enough. Back to the drawing board! Thanks for your advice.

Dennis - Thanks. I will clean everything carefully, lower the current and make sure I have plenty of stop-out (either varnish or sharpie) and see what happens next.