Stefan Trethan wrote:
> On Thu, 13 May 2004 07:24:08 -0700, Mark <mfraser@...> wrote:
>
>
>>Gun Blueing from your local hardware store.
>>Very slightly dampen a corner of a cloth with it, rub briskly.
>>You'll get a black sooty deposit if you put too much on / leave
>>it wet etc.; start with a less dampened corner of the cloth.
>>Keep rubbing....
>>
>>Same deal as prep for etching / plating - clean. Kitchen cleanser
>>like ajax etc. Wash well.
>>
>>Rubber gloves - it leaves a nasty odor that's hard to wash off.
>>Nothing terrible in the MSDS.
>>
>>CHeaper than most of the brass-blackening compounds in the few
>>hobby shops that sell them. Faster, too.
>>/mark
>>
>>
>
>
> Never seen anywhere around, thought about it too...
>
> I am on to something, left it immersed in strong NaOH solution mixed with
> sulphur overnight.
> It got black, very black, but the copper was etched :-( . Might work just
> fine if
> i only leave it for a short time.
>
I though sulfur was insoluble and therefore wouldn't have an
effect, but I'm no expert. I've seen copper site in some 50g/L
NaOH photoresists stripper solution overnight and came back next
morning to find a copper(II) oxide film ,i.e black.
The oxide will dissolve away in any acid.
Commercially they use sodium hypochlorite ("pool chlorine") mixed
with NaOH to make black oxide film on PCB s prior to lamination
of inner layers. Apparently the epoxy sticks a whole lot better
to Cu oxide than to the metal. I've never tried it but I think
the NaClO acts to massively speed up the oxidation rather than
relying on dissolved atmospheric oxygen. Worth a try....
Adam