On Tue, 3 Jan 2012, Al Shinn wrote:

> Sergio,
> I clearly stated "hardware store muriatic acid and drugstore hydrogen
> peroxide"  Should I have added "full strength"?

Al,
"full strength" would have been as useful as "good dollop" :-)

When I first came across this cupric chloride etching system a few years=20
ago, I was intrigued, so I decided to give it a try. I went out and bought=
=20
some concrete cleaner from a local hardware store (couldn't find muriatic=20
acid but I'd read that "muriatic acid" as supplied by a hardware store is=20
mainly used to clean brickwork and concrete AND the concrete cleaner I=20
found said it contained HCL). It's action on copper metal was very=20
disapointing with and without the drugstore H2O2. I tried forcing the=20
copper into solution by passing a current through it but this didn't help=20
much. I tried other things like bubbling air into the mix (as some other=20
recipes suggest).

So I resorted to using laboratory grade concentrated hydrochloric acid in=20
place of the concrete cleaner. Yep this worked very well but this stuff is=
=20
hard to get as a hobbyist.

Knowing a little bit about chemistry I was able to tell that the internet=20
homebrew recipe wasn't working. I wonder how many other people have=20
actually tried this and given up in frustration.

So, all in all, without knowing what concentrations are being used, some=20
people might get lucky and it works, while others just give up not=20
understanding what is going wrong.

> There would be only the smallest traces of copper left after
> precipitating with baking soda.  Copper is not like mercury or lead in
> that neither of them have a minimum daily requirement - copper does. We
> use copper pipes for our water, copper coated scrub thingeys, etc, etc.

But these traces are much higher than if the water were just passing=20
through a copper pipe.

> we used to use CuSO4 to kill roots in the sewer lines but that WAS tough
> on the sewage treatment plants.

We also used to use things like mercury and arsenic to treat things like=20
syphilis but that was tough on the patients. We frown on using mercury and=
=20
arsenic on people now just as we do on putting copper into sewers.

> If you wish to remove any final traces of copper, first test some of the
> suspect clear solution with a dollop of household ammonia, any
> significant copper will turn the resulting solution blue - if the test
> fails, electrolyze out the remaining copper or even just throw in some
> steel wool to scavenge the copper out.

The point isn't that I can remove traces of copper "if I wish to", it's=20
that ***EVERYONE*** who does home etching should be strongly encouraged=20
to.

> What I should have mentioned is that you should not throw away the
> solution anyway cause "they" say it regenerates with exposure to air and
> can be used over and over. I don't do that much etching so I toss mine.
>

Regards
Sergio Masci
--=20
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