I read an article by Peter Rowe explaining why, after you anneal
and pickle brass, the surface appears copper (the zinc in the brass
oxidizes more than the copper, so more zinc is removed by
pickling, leaving a surface higher in copper). He suggests heating
the brass only to about 850F to avoid this effect. So what I want
to know is this - how does one solder brass (or bronze) without the
color turning to copper?
Julie, I anneal and hard-solder brass all the time. As far as I
know, what happens is that (some of) the zinc fumes off at a lower
temperature, and the copper in the brass oxidizes. It always turns
black (CuO – removed by pickling) and red (Cu203). The red is not
just copper but is cuprous oxide. It needs to be bright-dipped to be
removed. I use dilute nitric acid for this, but the suggested method
using hydrogen peroxide+pickle also works (more slowly) and it’s the
method I use in my classes, since I don’t want to haul nitric acid
When I bright-dip, I stand and wait until it’s finished, so it won’t
get etched. Or, if it’s a cold day and the nitric acid is a little
slow, I set a timer for a few minutes to remind myself to get the
item out of the acid (I then rinse it well in water with some baking
soda in it, and then in plain water). Years ago, I forgot a pendant
in the acid and it etched all the way through, in places. However,
even that made a very nice variation – I soldered the remnant pieces
onto a backing. It was better than my original concept.
If you use the hydrogen peroxide + PhMinus method, you also have to
watch it, but mainly to see if it’s working. If there are not tiny
little bubbles rising off the surface, throw in some more H202. One
of my students once accidentally left his work in this solution
overnight, and it nearly “dissolved” entirely.
Both methods will usually yield a lovely matte surface, but if you
watch it, it won’t destroy a pattern.