From: Nash Computer Technology (nashcom@btinternet.com)
Date: 05/08/01-07:32:42 AM Z
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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