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Author Topic: Aging brass with ammonia, result copper!  (Read 11170 times)
Kevin C Cooper Esq
Zeppelin Captain
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United Kingdom United Kingdom


Asymetry is the bane of my life


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« on: March 14, 2010, 12:19:20 pm »

This might be of some use in your future endeavours, I was using some brass plated escutcheon pins as substitute rivets and thought they looked too bright, so I exposed them over night to ammonia fumes in a closed container and to my surprise they came out a strange blueish/silver colour. So I dumped them in vinegar for a while after which they emerged a dark shiny copper colour, not what i wanted but very attractive.
Food for thought? It will obviously vary according to the original plating length of exposure etc.
Kev.
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twilightbanana
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Netherlands Netherlands


« Reply #1 on: March 16, 2010, 09:25:59 pm »

I know that copper plating can be removed from steel by dunking the piece in ammonia; it forms a dark blue compound, which might be a large part of that blueish-silvery coating you found. The vinegar would have then reacted with the ammonia and might have caused the copper compound to be deposited as copper. Someone with more knowledge of chemistry would be able to tell you more.

As for ageing brass, what has worked for me is to clean the piece with soap and warm water to get any skin oils or manufacturing grease off, and to then suspend it above vinegar in an airtight container. A couple of hours should do the trick. Keep it out of the vinegar though; the piece I accidentally dropped in wouldn't tarnish with this method anymore after that.
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sidecar_jon
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« Reply #2 on: March 16, 2010, 10:26:50 pm »

I think what is happening is the brass is a mix of copper and zinc, the zinc is reacting and leaving the copper behind. Raw copper is very pink but goes to a more "coppery" colour in air very soon after exposure.

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twilightbanana
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Netherlands Netherlands


« Reply #3 on: March 18, 2010, 08:53:34 am »

Ah, of course. Then the first colour (or at least the silvery part) might also be the product of the ammonia dissolving the copper and leaving the zinc behind.

So...the thought occurs to me that one might be able to use ammonia and vinegar on brass sheet to turn different areas different colours.
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sidecar_jon
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« Reply #4 on: March 18, 2010, 09:22:10 pm »

Well yes, one could "de-zinc" parts and basically etch that bit, though the zinc is fairly intimately mixed with the copper so in effect the patches will be spongy bits of copper with the zinc gone.

I've found another way of making copper go green which is easy to paint on but as with all patinas is a bit fragile. Liquid plant food, the type i uses is green cheap and from a discount shop Lidles in the Uk.. though i bet a few others will work too..
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Gozdom
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Hungary Hungary

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« Reply #5 on: March 19, 2010, 02:51:16 am »

Must be copper sulphate, or mostly that. This goes under different names. You may want to heat it and apply it warm with a cloth or brush. I go for darker colours though, and polish the piece to make the etched pattern stick out as shiny naked brass. Dark reddish brown is easiest if you have CuSO4. Mix vinegar and sodium carbonate (available as a preservative in most supermarkets), let it react (thus producing sodium acetate), pour in the CuSO4 and water. Boil, immerse brass pieces, leave for 15 minutes to achieve patina. Then you can sand it back to reveal the etched ornaments.
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twilightbanana
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Netherlands Netherlands


« Reply #6 on: March 19, 2010, 09:47:55 am »

I just remembered this page of articles:

http://mailleartisans.org/articles/subcat.cgi?key=13

Especially the copper section would be of interest here. M.A.I.L is primarily concerned with making chainmail(le), but these techniques can be applied to any metal item.
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Capt. Stockings
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United States United States



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« Reply #7 on: March 23, 2010, 01:28:20 am »

I discovered the same thing by accident last December and posted about it here.

This is the effect I've gotten with acid only:

(Look at the heart, not the bow. I polished it a bit so the brass came through.)

This is the effect from a really long acid soak + heat:

(This time I scrubbed it with sandpaper to get the brass to show through.)
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rovingjack
Zeppelin Admiral
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United States United States



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« Reply #8 on: April 02, 2010, 06:30:13 am »

if memory serves zinc disolves in vinegar without current and copper usually requires vinegar and current to go into solution. so you may have oxidised and then disolved the zinc while leaving the copper behind. did you get a colour change in the solution, and if so what colour? That would indicate what metals went into solution.
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RandomTickTock
Deck Hand
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United States United States


« Reply #9 on: April 11, 2010, 09:43:01 pm »

I actually know the chemistry behind this. We did an entire lab focusing on the reactions of copper for my first semester chemistry course.

Copper compounds tend to react with ammonia forming copper(II) hydroxide and ammonia x-ide. In this case, it was probably copper oxide on the surface of the metal that caused the reaction.

After this reaction, another reaction takes places creating [Cu(NH3)4](OH)2 which is a blue precipitate when done in solution.

The silvery parts were likely the leftover zinc.

If anyone is curious, I can post the entire lab report.
« Last Edit: April 11, 2010, 09:45:56 pm by RandomTickTock » Logged
MalContent
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United States United States


Swindler, Con Man and Gentleman Thief


« Reply #10 on: April 12, 2010, 01:03:27 am »

I found this to be a wonderful tool for weathering an aging metal...I have used this on aluminum, brass, and steel....wonderfully fast acting and it can be sanded to clean it off or add some extra weathering.

http://www.birchwoodcasey.com/sport/blueing_index.asp?categoryID=1&subcat=5&prodcat=79

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