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Posted (edited)
On 3/2/2021 at 2:30 AM, JohnU said:

I have one problem with it. The blackening comes off easily. This is especially a problem for flat shim stock. The blackening comes of in flakes when rubbed.

 

Is there some trick to making it bond to the metal?

 

John

Further to my comments above cleanliness is vital as well.  The surface of brass is often treated with lacquer and even if not there is an oxide layer on the surface.  These areas will not blacken so the surface must be cleaned to remove these layers.  Often what happens is the surface is only partially cleaned.  What happens then is that only the clean areas blacken so the article does not seem black enough and we leave it longer.  Then multiple "flakey" layers build up in the clean areas  and eventually rub off.   In neat blackening agent full blackening should occur in about 10 sec.  In a 1:1 dilution - about 30 sec max.  If it takes longer than this your surface is still contaminated.

 

John

Edited by bartley
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Hi John,

 

That's interesting. I have not seem nonuniform formation. But the black is not stuck well. I've been chemically cleaning the brass before treatment. In the case of larger pieces I've been mechanically cleaning as well. After removing from the solution I rinse well in water for a minute or so.

 

That said, I do have the Flaking problem. I've left the brass in the solution for minutes rather than seconds. I'll try removing it sooner and see if that helps.

 

John

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John,

 

What is your cleaning method? If you think there is a lacquer coating you need a good acetone wash.  I then use a pickling solution but if you do this you must neutralise the pickling solution with bicarbonate and then wash this off before blackening.

 

John

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2 hours ago, JohnU said:

The brass is uncoated and I use Vinegar for cleaning. What's in the pickling solution?

OK John, pickling solution is chemically sodium metabisulphite. It is used by jewellery  people to clean metal and is sold in The US under the trade name Sparex, See here for some discussion of its use in blackening. It is a really good way of cleaning contaminants from brass but if you use it take care not to overdo it as it actually etches the surface of the brass and prolonged use will destroy minute detail.  I use 10 min at 60 degrees Celsius.

 

John

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Blacken-It was always my go to blackening chemical.  I finally ran out of it and cannot find it anywhere.  Why did they stop making it?  For brass I tried JAX and IMHO it is not nearly as good.  Pickling and cleaning, burnishing, etc and it still has flaking problems.   I love using  L.O.S. for copper, but does not work on brass.

 

In doing a little research I found Caswell plating and Caswell Antiquing-Metal finishing products with a chart for their various chemicals for steel, stainless steel, copper,  brass, bronze, silver, aluminum and nickel.    Some cross over for brass and copper.  Has anyone in our illustrious group tried it?  https://caswellplating.com/metal_finishing_solutions.html    I cannot find the chemical ingredients for Blacken It in order to compare if they are the same or at least similar to the Caswell products for brass and copper.   I just ordered a bottle of Birchwood Casey to give it a try on brass.  If it is as bad as JAX I will try the Caswell product, especially if a member has tried it and gives it some praise.

 

Allan

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Blacken-It was made by a married couple - very small business.  They died in a car accident - or so I read back when it happened - and the company died with them.  I imagine the EPA scares off any small business that would dare think of replacing the product.

 

Birchwood Casey Brass Black is my standby.  Make sure the metal is clean, dip the pieces in it either dilute or full strength remove and let it drain off.  Repeat as necessary and then was it off let the parts air dry and then rub gently with an old T-Shirt.  Some black will rub off.  If not black enough repeat the process.

 

I was never happy with Blacken-It and had switched to Brass Black when Blacken-It was still being made.

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12 hours ago, allanyed said:

 

 

In doing a little research I found Caswell plating and Caswell Antiquing-Metal finishing products with a chart for their various chemicals for steel, stainless steel, copper,  brass, bronze, silver, aluminum and nickel.    Some cross over for brass and copper.  Has anyone in our illustrious group tried it?  https://caswellplating.com/metal_finishing_solutions.html    I cannot find the chemical ingredients for Blacken It in order to compare if they are the same or at least similar to the Caswell products for brass and copper.   I just ordered a bottle of Birchwood Casey to give it a try on brass.  If it is as bad as JAX I will try the Caswell product, especially if a member has tried it and gives it some praise.

 

Allan

 

Modelers certainly do not need to know much chemistry but for the record I have covered it here.  I have not used the Caswell product but its composition seems similar to Birchwood Casey in that it contains both selenious acid and molybdate and the acid is phosphoric.  The concentration of these products varies but I would recommend diluting then to slow down the reaction.  This seems to delay the build up of the "flakey" material which rubs off.

 

John

 

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