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Topic: Curious about this patina process.  (Read 6657 times)

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Offline moose

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Curious about this patina process.
« on: June 14, 2010, 08:21:16 PM »
Hello everybody,

My name is Sam and this is the first post I have made here on Chemical Forums. I am a furniture maker and generalist who finds the science behind the things I make very fascinating. In my most recent piece of furniture I have been working to create a brown patina on some furniture hardware. I found a product called Plum Brown. According to the MSDS The contents are as follows:

Sodium Nitrate         NaNO3
Potassium Chlorate   KClO3
Copper Chloride        CuCl2
Nitric Acid               HNO3
Water                     H20

The patina process involves heating a piece of iron to 300*C and applying the products onto the hot iron to form a brown rust colored patina (Iron Oxide??)

I am very curious about the process and what exactly is happening. If anyone can help me to understand the reaction in the form of equations I would greatly appreciate it.

If you are interested in seeing the patina please take a look at my blog where I have a photo posted.


correawoodworks.wordpress.com


Thanks for any help you can offer
-Sam Correa

« Last Edit: June 14, 2010, 08:53:29 PM by moose »

Offline hobobot

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Re: Curious about this patina process.
« Reply #1 on: June 15, 2010, 03:14:01 PM »
Not sure about the exact equations. But I think the purpose of those ingredients is to produce O2 to speed up the rust process. Except, I think the CuCl2 may just be for color.
You could experiment with your own solutions. Acids in general (even vinegar) will speed up the oxidation.
Hydrogen Peroxide and Bleach will produce O2 gas, which may work too. (But I've never tried that one. Stick to store-bought low concentrations.)

I don't know if it works on metal, but Potassium permanganate will create an aged look on wood, cloth, and glass.

Offline moose

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Re: Curious about this patina process.
« Reply #2 on: June 16, 2010, 02:21:13 AM »
The oxidation of the products makes sense and I imagine that the Nitric Acid would etch the surface of the iron to increase the surface area which I imagine would also increase the rate at which iron oxide could form. I am guessing that the copper chloride forms both copper and sodium chloride. The patina certainly has a copper iridescence to it.

As far as other chemicals I use in woodworking. Often I fume 28% ammonium hydroxide (nasty base) to react with tannic acid in white oak to form ammonium tannate. The oak takes on a grey color and increases the contrast between the medullary rays (low concentrations of tannic acid) and regular sclerenchymatous cells (high concentrations of tannic acid) of the wood.

I have read about the use of potassium permanganate on cherry hardwood to give it a much older appearance but it can go too far very quickly and make the wood almost black in color.

Thanks for your thoughts hobobot.

-Sam

Offline billnotgatez

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Re: Curious about this patina process.
« Reply #3 on: June 16, 2010, 07:58:37 AM »
moose-
I am curious as to where you purchase some of the chemicals you use.Where do you get the ammonium hydroxide and the rest.

Offline moose

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Re: Curious about this patina process.
« Reply #4 on: June 16, 2010, 08:21:42 AM »
I get them at a wholesale chemical supply center known as Hill Brothers. You need to have a license to purchase from them and some of the higher molarity concentrations and more caustic chemicals require special certifications to purchase. Aqueous ammonia is commonly used in the printing industry as well as meat packing. You may be able to find it at print supply distributors but more often they have switched over to digital machines which do not use these chemicals.

Offline skyjumper

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Re: Curious about this patina process.
« Reply #5 on: June 16, 2010, 02:25:46 PM »
United Nuclear. Especially if you live near their store, you can get a ton of reagents. Fairly inexpensively 

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