Hi Phil,
Is the solution a clear emerald green at the moment? If so I would guess
that you are short of acid. If it is murky and more an olive-brown
colour then it needs more oxygen.
Bubbling air through the solution can take a long time. Adding H2O2 is a
lot faster. My etch tank is quite small (1.5 litre). It does not take
long for the available oxygen to become exhausted. A teaspoon of
100volume H2O2 is enough to get it etching well again. If the solution
starts fizzing when you add the H2O2 and has a chlorine smell you have
added too much.
Les
Phil wrote:
> I mixed up a batch of HCl and H2O2 and got good etching (which was
> mostly from the HCl). There were some bubbles but no chlorine gas. I
> etched 6 double sided boards that were on average 20x20 CM in the
> first session. The etchant turned the well described emerald green.
> 3 days later, I went to etch another board and got no (or r-e-a-l-l-y
> slow) progress. I bubbled it for about 18 hrs total (with 2 airstones
> - lots of bubbles). Still no etching.
>
> I got a hydrometer and the density is 1.075. This is well below the
> 1.17 recommended by
> <http://users.rcn.com/rexa/Projects/CuCl_ech.html>. From the HCl and
> H2O2 I put in, the s.g. should have been 1.029 so I assume that the
> difference, 0.046, is from the etched copper in the form of CuCl. It
> appears I have too weak a cucl solution by about 1/4 but I'm not 100%
> sure about the chemistry here. Everything I've read says that it
> doesn't take much copper at all so I'm a bit at a loss here. I need
> to get pH measuring capability but the density is clearly wrong.
>
> Any suggestions for fixing? The page mentioned above recommends CuCl
> salts which I have no idea where to get and probably shouldn't have to.
>
> I'm going to put a couple pieces of copper in over night to see if I
> can get more copper into solution but its not clear to me that will
> actually work.
>
>
>
>
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