Finally I have returned to trying electro etching again. I had several goes at mild steel using concentrated sodium chloride. The last attempt involved two small pieces, side-by-side, using identical preparation (cleaning, negative pattern transfer by Press-n-Peel, re-touch with Porcelaine pen and back-spraying with Dupli-color primer.)

One piece I dumped into a cold (25 degC) Edinburgh Etch for 50 minutes. The other I etched in the salt solution using 0.3 Amps current for 30 minutes.

Even as I was washing off the second piece with distilled water the resist started to peel around the edges. There was a significant amount of foul biting which was quite deep and could not be got rid off by surface abrasion without attacking the pattern itself.

The other piece came out very nicely although the etch was nowhere near as deep.

Does anyone have experience with this? Is the salt solution really that aggressive towards resists (I had the same thing happen when I was using my favourite resist for hand work - the Duplicolor primer)? Is this a function of the electrolyte concentration (the info on desirable concentration for this process seems scarce)?

As far as I can tell all that happens during this process is the transfer of iron ions into the solution where they are precipitated by hydroxyl groups into ferrous hydroxide (a green sludge). The other half of water molecule is released as hydrogen gas (bubbles ++). Could it be the hydrogen formation that lifts off the resist?

I can see a hundred experiments with this process in the future to get it right but it would be nice if someone could provide a bit of a short-cut :-)