Hello,

We use Ferric Chloride in a spray etching application to etch 304 Stainless
Steel. We are having problems and cannot determine what they are. We do not
have a scientific background and are just looking for a few simple answers.
When the bath is new it seems to work beautifully. Then at some point we
start to get peculiar undesirable results.

We use 45 Baume Ferric Chloride and etch at 45°. The Ferric is less than 3%
hyrdro-chloric acid when received.

The following website I put up clearly demonstrates the problems with
photos.

http://www.precisionsigns.com/badetchingindex.htm

1.) What is actually happening in these pictures? Is part of the steel
decomposing faster than other parts?

2.) What measuring equipment should we be using to monitor the Ferric
Chloride? We have been measuring it's Baume with a hydrometer but should we
also be measuring the pH or anything else? If so, what type of instruments
and what are the ranges that they need to be?

3.) I've heard of regeneration. Is regeneration of the Ferric Chloride safe
to do with HCL (Muriatic)? By safe I mean are there any harmful / flammable
fumes generated? Do I need to make sure that the HCL stays at 3%? And how
much tolerance is there with it?

I feel like I'm on the right track here but need some good advice or
confirmation.