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Old 23rd Jan 2020, 7:14 pm   #21
G4_Pete
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Default Re: Black oxide coating on brass

I dont think Lead Acetate is a good way forward I used to work with the stuff in gas detectors and can only re iterate wikipedias toxicity warning.

However I have just spent some time cleaning off some brass that had gone black due to leaking alkaline batteries - more nasty stuff but it certainly left a very hard to remove black coating on the brass parts.

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Old 23rd Jan 2020, 10:58 pm   #22
rambo1152
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Default Re: Black oxide coating on brass

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I thought the gongs were made black through a plate process? I thought I read that the brass had to be plated with copper before the blackening could happen.
Interesting you should say that. When I removed the black from the gongs of my No 1A Bell 40+ years ago (when I knew no better) I always thought the polished bare metal looked more like copper than brass. I've just removed the gongs and had a close look, and where the nut was screwed down the brass is showing, and is quite a contrast to the rest which looks orange in comparison.

I tried to photograph this difference in emissivity without success.
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Old 23rd Jan 2020, 11:37 pm   #23
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Default Re: Black oxide coating on brass

When I used to do my own black and white photography, I found that spillage of exhausted fixer would silver plate the pennies I used to use under the fixer dishes to level them up. The plating was initially black, but would readily buff up shiny using a cloth. I found it worked on the brass door knobs of our prefects' room. If
left the silver plating would soon blacken. Finding someone who still uses traditional processing that used fixer could be cadged from might be less difficult than trying to source toxic chemicals. The fixer should ideally be as exhausted as possible: fresh fixer contains no silver.
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Old 26th Jan 2020, 6:48 pm   #24
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Default Re: Black oxide coating on brass

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When I used to do my own black and white photography, I found that spillage of exhausted fixer would silver plate the pennies I used to use under the fixer dishes to level them up. The plating was initially black, but would readily buff up shiny using a cloth. I found it worked on the brass door knobs of our prefects' room. If
left the silver plating would soon blacken. Finding someone who still uses traditional processing that used fixer could be cadged from might be less difficult than trying to source toxic chemicals. The fixer should ideally be as exhausted as possible: fresh fixer contains no silver.
My dad and I kept our working strength chemicals in glass pop bottles, I don't think it occurred to either of us it wasn't the best idea. Anyway, Accutol & Accufix were expensive, so we kept the solutions as long as possible. I was interested in plating (electroplating) so I missed a trick there.
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Old 29th Jan 2020, 11:45 am   #25
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Default Re: Black oxide coating on brass

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Finding someone who still uses traditional processing that used fixer could be cadged from might be less difficult than trying to source toxic chemicals. The fixer should ideally be as exhausted as possible: fresh fixer contains no silver.
I still do my own black and white developing. Looks like I'll have to stop ditching my fixer-mix (Ilford rapid fixer) after about a dozen films or so and let it mature a bit! I've heard of particles of silver being visible in the bottom of folks' fixer bottles but I like to change mine when it still has some zing in it.

I'd need to develop a fair few films to acquire enough silver to blacken the gongs on my bellset No: 20 though.
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Old 29th Jan 2020, 1:40 pm   #26
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Default Re: Black oxide coating on brass

I used to use M&B Amfix, which fixed in 2 mins, as the 10 min time of ordinary fixer was the bottleneck in processing prints. I normally used to do well over 100 prints in a session. I actually read the leaflet that came with it, and noted they recommended the two bath approach, where you kept separate A and B solutions. 2 mins in A, followed by 2 mins in B. This meant that if A became exhausted during a session, B would complete the fixing. When A tested as exhausted (by failing to clear a scrap of undeveloped 35mm leader), A was discarded (or put aside for plating), B became A, and a fresh solution was made up for the new B. This ensured that the maximum life was squeezed out of the relatively expensive Amfix (which I used to buy in half gallon bottles for economy) and ensured that I never had any problems with prints deteriorating due to incomplete fixing. It also meant that my exhausted fixer was absolutely saturated with silver.

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Old 29th Jan 2020, 3:02 pm   #27
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'...ensured that I never had any problems with prints deteriorating due to incomplete fixing. It also meant that my exhausted fixer was absolutely saturated with silver.'
I don't have a darkroom any more, so just develop film in a dark bag and scan the negs. I use Ilford rapid fixer but always leave it for about five mins at least (you can't over-fix film!). Once I get a 'retirement' darkroom made I'll use enough fixer to harvest the waste silver.

I used to use Paterson Acufix (An Accufix is a LORAN receiver made by Megapulse, which is probably why it tripped off the fingers so readily!) when we had a works 'club' darkroom back in the early '90s and I used to print there.
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