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Chemical Blackening - Dip or Paint


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I have just used my usual technique (I say usual - about once in 6 months) of preparing wheels for blackening.

 

This involves physical pre clean of the surface with a glassfibre pen and then a good wash in IPA to remove finger grease.

 

I then paint on a liberal coat of Carr's metal black and leave for about an hour, rinse in warm water then repeat with another coat.

 

In the past this has generally given reasonable results - but on this occasion the results were not so good. In fact very uneven.

 

I was wondering if I could learn anything new...

is dipping better than painting?

is there a better preparation technique?

should it be left longer? more coats?

 

 

So we are talking typical loco wheels with brass or n/s balance weights.

 

I should add before the suggestions come i - that I have never found felt tip pens or paint satisfactory - the former comes off when I clean the wheels with IPA and the later does not conduct power especially well.

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I have just used my usual technique (I say usual - about once in 6 months) of preparing wheels for blackening.

 

This involves physical pre clean of the surface with a glassfibre pen and then a good wash in IPA to remove finger grease.

 

I then paint on a liberal coat of Carr's metal black and leave for about an hour, rinse in warm water then repeat with another coat.

 

In the past this has generally given reasonable results - but on this occasion the results were not so good. In fact very uneven.

 

I was wondering if I could learn anything new...

is dipping better than painting?

is there a better preparation technique?

should it be left longer? more coats?

 

 

 

So we are talking typical loco wheels with brass or n/s balance weights.

 

I should add before the suggestions come i - that I have never found felt tip pens or paint satisfactory - the former comes off when I clean the wheels with IPA and the later does not conduct power especially well.

Kenton,

 

Dip!! total immersion, and continuous agitation, clean off the metal, de-grease with IPA, but then wash with ammonia, and rinse, before blackening with hand warmed solution, whatever type.



 

Brass is not consistent, it varies and there are dozens of types, which all black differently. Some leaded rod will not black at all. I worked with blackening for cameras and lens, scientific instruments etc, and have used all the processes, but gunblack is the easiest, and safest, to use at home. Gun black will work with steel, brass, and some nickel siver, but Carrs do a special version for Nickel.......

 

For brass........ the best process is pure copper carbonate (reagent), dissolved till it will not take more, in very strong pure ammonia at 60oc, and then the ultra cleaned in IPA item is immersed in hot 60oc copper carbonate, solution for about 20 secs. (Experiment is needed for each batch of brass to get exact timings).

 

Result....... is very Dark brown/ Black and quite durable. ... and shot lungs, the fumes are awful..........This is the "secret" process used to "bronze" base brass in the Victorian period,...an art trade secret to turn cheap castings into bronze.....

Stephen


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For brass........ the best process is pure copper carbonate (reagent), dissolved till it will not take more, in very strong pure ammonia at 60oc, and then the ultra cleaned in IPA item is immersed in hot 60oc copper carbonate, solution for about 20 secs. (Experiment is needed for each batch of brass to get exact timings).

Doesn't seem to me to be a practical proposition in the average domestic environment!

 

(PS Stephen, do you need to use such a large font?)

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Thanks Stephen

ammonia solution? where does one find that in the kitchen these days ;) certainly sounds a good tip and something definitely missing from my process.

 

But, I don't think I'll be heating the solution up to 60'C - the warnings all over the bottle make it an arms length, gloves on task as it is. But surely the temperature is just to speed up the process? I'm in no rush.

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I've used Carrs blackening for brass loads of times and it usually works well, the only thing I have found is you need to mix it 50/50 with water otherwise the blackening just flakes off in places leaving an unsatisfactory mottled effect. Needless to say everything has to be clean before you start. You only need to put the brass in the solution for 2 or three minutes to give the desired results.

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Well had another go.

Couldn't source any ammonia.

So just scoured all the metal again with the g/f pen and washed in IPA only handling with tweezers. Dunked 2 wheels in the solution for about 5 minutes stirring regularly.

 

Result is this:

nb040dh_107.jpg

 

Probably worse than last time. The wheel rims are not too bad they look worse under this magnification than they do by eye. But there is still quite distinct glinting patches. :(

I don't remember all this trouble last time.

BTW the jar is relatively new and unused - picked up at the Manchester show.

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Doesn't seem to me to be a practical proposition in the average domestic environment!

 

(PS Stephen, do you need to use such a large font?)

 

font number is equal to normal size of windows text, plus one setting, default is very small at half of default microsoft, maybe it's your settigs, this is set on two computers with different monitors running default Microsoft and definitions for the screen. I have no control over how a monitor remotely shows the text

 

Stephen

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Two things, the ammonia only refers to the carbonate process, and the wheels are being done with brass and steel, or nickel and steel in contact with the solution at the same time, and this is never a good idea.

 

Steel and brass must be separate, and Gun black or Carrs used hand warm only, not 60 oc.

The steel would be done with latex liquid mask, (or temp paint) over the over bits, done and completed, and then the other parts done with latex mask on the blackened bits. Temp paint can be any cellulose type, which washes away with thinners.

 

The two metals in the solution will set up un-predictable electrolytic action within the solution, and result in exactly what you have, very crystalline and patchy blackening indeed.

 

Once partly blackened it may not be able to reliably repeat to complete the carbonate blackening , without very careful removal, totally, no remaining blackening, even at microscopic levels. but Gun black is not too bad, it is designed to act even on patchy blackening already there, so try again.

 

Carr's is essentially Gun black, (there are several formulae, copper sulphate or selenium), and can be repeated till right, so brush off, and continue with more solution.

 

(set in de-fault size, +1)

 

Stephen

 

 

.

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I use Birchwood Casey instead but i've been dipping to save getting a brush out, it does seem to produce a better result. Ironically though the thing that blackens best is always the pliers!

 

It will, they are steel, and multiple dips will re-blacken them nicely!......

 

Stephen

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the wheels are being done with brass and steel, or nickel and steel in contact with the solution at the same time, and this is never a good idea.

 

Steel and brass must be separate

 

Um - that sounds like an error then.

I guess it worked last time because I painted it on. But for some reason failed this time.

 

Evidently dunking them was NOT such a good idea this time :(

 

I'm not sure I would go to all the bother to paint them with a mask, blacken, remove mask, repaint blackened parts with a mask and then blacken the other bits and finally remove the other mask.... in fact I am sure I wouldn't and just simply paint the balance weights black anyway.

... probably what I will do now to try to recover the situation.

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I know you've cleaned it with the glass fibre but could it be superglue still stuck on very finely from where you glued the balance weights on? I don't think i've had something that blotchy but then I haven't blackened brass and steel at the same time.

 

font number is equal to normal size of windows text, plus one setting, default is very small at half of default microsoft, maybe it's your settigs, this is set on two computers with different monitors running default Microsoft and definitions for the screen. I have no control over how a monitor remotely shows the text

Stephen

If you find the default text size quite small use ctrl and + in your browser which should increase the text size. I find the default adequate and it keeps all posts identical, the control mentioned can make everything bigger/smaller for the reader as they wish.

 

Your posts do come out a lot larger because you've been setting them bigger than normal. I'm hoping Andy turns off the font/size selections when he has a chance to tweak the forum software.

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I've been using Liberon bronzing / blackening fluids, sold for the antiques restoration trade... This stuff seems to work quite well on several different metals, is cheap, & doesn't need any warming. For a working solution, dilute about 1:3 with water in a clean jar, chuck the bits in, shake gently & watch em go black... Remove as soon as they achieve the right colour, & rinse in clean water.. The black comes off if you leave it in too long, turning powdery, but well worth a try...

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I know you've cleaned it with the glass fibre but could it be superglue still stuck on very finely from where you glued the balance weights on?

I suppose that is possible - especially along the edges of the brass where they are in contact with the brass and the glass fibre pen wouldn't reach. But in the middle of the face where there was no superglue?

I believe it may be a combination of the two metal types and still leaving it in too long. I will have another go at just painting it on the brass later today.

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I suppose that is possible - especially along the edges of the brass where they are in contact with the brass and the glass fibre pen wouldn't reach. But in the middle of the face where there was no superglue?

I believe it may be a combination of the two metal types and still leaving it in too long. I will have another go at just painting it on the brass later today.

 

If you use a brush, make sure it is plastic if possible, no metal ferrule, as this can react with the chemical solutions. The Liberon blackener is very good, it's a brown black to imitate bronzing, but is expensive, and Liberon have dropped some products from the range recently, and it may not be available widely.

 

Also if the Liberon type is used, then the oxides penetrate the brass surface and will not easily remove to try another type of solution, basically whatever solution is used, you must continue with the same one on re-trying the process.

Once selenium based ones are used, the copper based ones fail to react.

 

I notice "warming" is being taken to literally, I mean about hand warm, as distinctly cold, say under 40f, would slow the processes dramatically, all blackening should be done just warm at about 60f/ 20c or so, or a bit more. The Copper Carbonate process is different, hot water at 60c+ is used, and lower will not work, but it is not a process to do at home anyway, the gun black is safer and reliable.

 

Stephen

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I'm sticking with Carr's - simply for no other reason than I have it - but take the point not to mix and match anyway.

 

The third attempt is a bit better than the other two and I'm drawing a line there - the wheel rims and the brass are show signs of distress, a bit like me. Perhaps next time I will dip the parts separately before adding them.

 

nb040dh_108.jpg

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