Carr's Metal Black for Brass

How is one supposed to use it?
I brushed it on with mediocre results. Maybe I should have cleaned the brass more?
MBQ

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snipped-for-privacy@hotmail.com wrote:

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 that)
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 metals.
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Paul Boyd
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Is it OK to dunk in the original container, or will that lead to the contents of the container going off in some way, eventually?
MBQ
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Man at B&Q wrote:

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.
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Paul Boyd wrote:

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.
cheers,
wolf k.
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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)?
MBQ
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Man at B&Q wrote:
[...]

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.
cheers,
wolf k.
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Wolf K wrote:

Yet Martyn Welch, he of the weathering bible, uses cotton buds to apply the stuff, rubbing it in. Never worked for me either...
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snipped-for-privacy@hotmail.com wrote:

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 metal blackener.
Caution: metal blackening solutions are mixes of ferrous/ferric chlorides and selenium salts. These are toxic, so use "rubber" gloves and eye protection.
cheers,
wolf k.
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