Hi Tony,
From what you describe, it sounds to me like the acid has probably reacted about as much as it can with the metal. As the molecules of the acid react with the metal, new compounds are created (such as gases), and eventually there will be few acid molecules in a state to react with the metal.
I'd try getting fresh acid and trying the same type of metal again. I suspect it wil act vigorously.
It's been 17 years since I've last done acid-etching. I forget what processes may be available to "rejuvenate" or strenghten the acid. I worked mostly in non-ferrus metals. You certainly hit on a big issue in industrial chemistry - properly dealing with the byproducts.
Good Luck.
Thad Weakley
Ann Arbor, Michigan 42.2N 83.8W
tony mo! ss <[EMAIL PROTECTED]> wrote:
Fellow Shadow Watchers,
Some time ago I suffered puzzling failures when
attempting to etch stainless steel using ferric chloride alone. Nothing
seemed to happen until the 'resist' was removed to reveal that the
exposed steel was untouched whereas the protected areas had etched
heavily. What a bewildering surprise! Negative etching!
Thanks to advice from List members and a web search I experimented
successfully with a cocktail of nitric and hydrochloric acids mixed with
ferric chloride and this gave excellent results on a couple of plates
although strong ventilation was essential to carry off the nasty vapours.
The next surprise came with the third plate etched in this same mixture.
Gone was the previous fizzing activity at the surface so I extended the
etch time. On r! emoval there was *some* effect in that the dial imprint
had appeared on the steel surface but more as a pale change of colour
rather than a deep cut.
Mmmmh!!?? Could this have been because this was an 'offcut' of stainless
steel bought from a local fabrication shop rather than my usual supplier?
Yes...that must be it!
So in went the plate's twin sister to be etched on steel from a batch
successfully treated previously. No fizzing at the surface again! Panic!
Could it be just lower temperature? My immersible glass tank heater soon
had it steaming but, despite immersion for three time the previous
successful times, the previous pale image was the only result.
As a non-chemist I have to ask what is happening here? Is the acid so
quickly exhausted or whatever? With ferric chloride on brass/bronze I
can deep-etch a large number plates with perhaps only an increase in tank
time.
This would make etching stainless stee! l a prohibitively costly process in
materials and also in the hassle of neutralising for disposal etc.
Any thoughts on this matter would be most welcome.
Tony Moss
---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
What are the most popular cars? Find out at Yahoo! Autos
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
