Homebrew PCBs

Thanks again, Adam-

I found an inexpensive balance made in India for C$15 and it is
remarkably sensitive, comparing the weights included against those of
Canadian coins, whose weight is listed by the mint on the web.

I also found an inexpensive source of indicators in the US who will
send them up here.

After 12 hours with the airstone I don't see any change in etchant
color. The ph was still at 3 today so I added the bit of HCl left in
the 4 litre jug. I will get more airstones as you suggest, and see
what happens.

Grant

--- In Homebrew_PCBs@yahoogroups.com, adam Seychell
<adam_seychell@y...> wrote:
> The etchant HCl and copper can very widely and work ok. Make 
> up the 1.0M standard NaOH solution by dissolving 40.0g of 
> NaOH in liter of water, store in polyethylene bottle. You 
> will need access to some scales +-1g or better. You should 
> only ever need to to this once. Then use the eye dropper 
> technique to get a rough estimate of free HCl.
> You really need an pH indicator because I found that by 
> simply looking for copper hydroxide formation is very 
> difficult. The indicator must change color before about pH 
> 4.0, because the copper chloride seems to hold the pH around 
>   there while its converted to copper hydroxide.
> I use methyl orange pH 3.1 ~ 4.4. Unfortunately phenol red 
> sold at pool stores changes at pH 6.8 ~ 8.4.
> Maybe you can stick in pH paper and watch for a color 
> change. I found long list of indicators.
> http://chemdat.merck.de/cdrl/services/labtools/en/table_abindic.html
> 
> It sounds like there is plenty of acid because you talk 
> about fumes and the fact a drop turns clear after some time. 
> I would of got more than one 12" air stone, or as many as 
> the pump can handle. You can leave the airstones in 
> permanently and have a second air hose specifically for 
> regeneration.