> in which case you should get a much better yield using a tall thin
> container rather than a shallow one as on average the free chlorine will
> have to travel farther before leaving solution and have a greater chance
> of reacting.  some copper wool (if such a thing exist, i'm not sure...)
> or possibly even brass wool on top would likely reduce fumes.

In practicality 'yield' isn't realy a concern. None of the chemistry here
is expensive enough or toxic enough for that to be a concern. I'd also be
very careful about the brass, this etchant will etch most anything -
including stainless steel - using brass or other metals will seriously
complicate the regeneration proccess.

> keeping the lid on and putting a rag over it when bubbling is an
> excellent way to eliminate any mist, provided you wear gloves when
> removing the rag and wash it promptly since it will have some free
> etchant/acid on it.

Of course, standard safety protocols should be followed - gloves, goggles
ect, an apron whouldn't be a bad idea... :o)

> very interesting chemistry, and interesting that it works so quickly.

Standard etch times for a batch of 'mature' etchant that's been regenerated
the day before runs about 8 - 11 minutes, with no chlorine gas production.
Adding excess H2O2 will produce offensive chlorine, but can etch in less
than 30 seconds. - I don't reccomend it.

> for what it's worth, if you can get them to sell it to you, a beauty
> supply store should have fairly concentrated hydrogen peroxide.  i
> haven't tried to buy it but normally you are supposed to have a
> beauticians license to buy anything from them in this state, though i
> don't know how strictly enforced that is and if they might not be happy
> to sell it after you convinced them you weren't dying hair with it.  i'd

A larger 'chain' store I tried only had prepackaged 'products'. Though I'm
sure some of them contained peroxide, purity and strength were
indeterminite and I just chose to avoid the complication. There's a good
chance other stores might have it though, I quit looking.

> think you might also be able to bubble oxygen through it (you'd need a
> plastic diffuser for the gas to make small bubbles, smallparts.com has
> such plastic/teflon items) particularly since air will do it.  i'd also
> think that a fine diffuser would make the air method work faster with
> less evaporation (and smaller bubbles should produce less mist).  it
> might or might not be worth the expense and trouble.

Air works alright, so I don't see a benifit to going to strait oxygen. I
use an aquarium pump, silicone hose and plastic difuser from my local
walmart. A rubbermaid cerial keeper works fine for the tank, total
cost -about $25.

> now, if any one can come up with a way to do real through hole plating,
> that would be exciting (in which case you normally drill the board
> first, convince some fine metal to line the holes, and then electroplate
> copper into the holes and the board surface, which is why board houses
> start with 1/2 oz copper to make 1 oz copper boards, and then etch it).

Check out the yahoo group I mentioned earlier, there's a guy on there that
does homebrew through hole plating. But I think his setup is rather
extensive.

> i'd just love to be able to make real through hole boards for
> prototyping and i have the space to do it once i get the garage
> organized (my 4' by 8' table with pvc on the top would be perfect if i
> got water out there, which i was already planing to do).
>
> it's fantastic that it's a continuous cycle without waste! (other than
> chlorine, which is already released from pools and when people use
> bleach and not yet very regulated, i don't know if it should be or not,
> probably not for small volumes)  now i see why many board houses do it
> that way.

Maybe I mistyped somewhere, but the etchant should *not* release chlorine
during normal operation. The chlorine should be combined with the copper in
the bath. It only escapes when there's an excess of free oxygen (impossible
to do with an air bubbler) and no copper available. A condition normally
only seen when starting a CuCl in this way.

It's also interesting to note that many board houses do not use this
etchant. Some processes use tin plating as an etch resist, CuCl will
happily etch the tin too.

-Denny


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