The brass does need to be very clean - Carrs also sell Acidip which is
quite effective at cleaning up the brass - dunk it and scrub with an old
toothbrush (or a new one if you buy the 4-pack for 30p from Morrisons!)
Brushing on the blacking can work, but I prefer to dunk the brass. It
may come out a bit powdery, but some work with a brass brush in a
mini-drill cleans things up nicely (don't breathe the dust in from doing
Nothing wrong with the Carr's stuff, but you might also have a look for
Birchwood Casey Gun Blue, which comes in various concoctions for various
Good question! I nearly always pour enough into a separate container,
and chuck it away when done. Sometimes though, it seems such a waste so
I pour it back into the original container! I suppose it must lose its
effectiveness eventually, but the bottle is usually empty before I get
to that point.
Actually, the reagent is used up - so quickly, that brushing the stuff
on will lead to streaks and blotches. The stuff works by depositing a
selenium compound on the brass (or other metal), which of course uses up
the selenium in it.
This reaction uses so much selenium, that brushing the stuff onto the
metal part will result in streaks and blotches, as the thin layer of
reagent has very little selenium in it, which is deposited almost instantly.
That's exactly what I found, but I think it was more to do with
surface preparation. A quick rub with 600 grit wet & dry made it work
a whole lot better.
I found it carries on working. Coming back a few minutes later, the
pieces were even blacker still.
Are we talking about the same stuff?
Someone somwhere suggested it for blackening the sides of rails. This
works, but will it harm the sleeper web (peco)?
Basically yes, but different manufacturers will concoct slightly
different formulations (proportions of reagents, mostly).
It won't harm plastic. Some people have experienced slow deterioration
of solder joints, however, but that seems to depend on the precise
formulation - the buffer salts vary somewhat between brands (they're
needed to prevent reagents from reacting with each other in the bottle.)
I suspect that acid fluxes are more of a problem, though.
Metal must be very clean - the slightest amount of grease or oil blocks
the contact between reagent and metal.
Use an organic (citrus-based) cleaner, then washing up detergent
_without_ perfume of skin-softeners etc. Air dry both times. You could
then etch slightly with vinegar + salt solution - takes a few seconds,
it's done when the brass is uniformly bright. Rinse, dry, and apply
Caution: metal blackening solutions are mixes of ferrous/ferric
chlorides and selenium salts. These are toxic, so use "rubber" gloves
and eye protection.
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