From: Joachim (joachim@microdsi.net)
Date: 05/08/01-11:28:45 AM Z
To make an effective pinhole lens with brass shims I have not found it
necessary to blacken the brass. I do not get light bounce or any suggestion
of flare at all so long I have painted (carefully) reasonably close to the
aperature with flat black. Joachim
> -----Original Message-----
> From: Nash Computer Technology [mailto:nashcom@btinternet.com]
> Sent: Tuesday, May 08, 2001 9:33 AM
> To: Alt Photo
> Subject: Chemistry advice
>
>
> Hi
>
> I've read some old journals on making pinholes, and they seem to suggest
> using brass or silver sheet. I've made a couple in very thin brass sheet,
> and now need to 'blacken' the inside edges of the pinhole. In the old
> journals (1900-ish) they suggested leaving the brass in a mixture
> of dilute
> hydrochloric acid and sodium thiosulphate.
>
> I bought some 10% solution hydochloric acid and poured out about
> 100ml into
> a glass jar. I then added a small amount of sodium thiosulphate
> (less than
> one quarter teaspoon). When I drop in the pinhole, the brass starts to
> darken. After about 10 minutes it appears to have a black-ish
> coating that
> can flake off if handled too aggresively such as when trying to pick it up
> with a teaspoon. The first one I left in too long, and ended up with more
> holes than the original pinhole... Although it seems to do the trick, the
> brass appears to end up with a rougher texture, although the edge of the
> pinhole seems smooth enough.
>
> I just wondered if anyone knew of a better way to make blacken
> brass, or if
> I need to modify my technique.
>
> For those who worry about these things, I've been wearing a 3M rubber face
> mask, goggles and gloves, and working outdoors.
>
>
>
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