Does anyone know the active ingredients in blackening solution (commonly used to blacken items such metal tank tracks and chain)?
Thanks,
Paul
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I believe muriatic acid to be one of the common ones.
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I sold industrial, reagent and USP grade chemicals for more than a decade. The art of patinizing metals is a bit like alchemy, closely guarded secret formulas, obscure, archaic chemical names, noxious fumes and hazardous procedures. That being said, by far the most common compound used for producing a dark brown to black patina on many common metals is the very corrosive, nasty smelling, humorously named, “Liver of Sulfur”, “a loosely defined mixture of potassium sulfide, potassium polysulfide, potassium thiosulfate, and likely potassium bisulfide”, to quote Wikipedia. https://en.wikipedia.org/wiki/Liver_of_sulfur.
I sold a lot of this stuff. The problem is that it reacts differently on different types of metals. “White metal”, commonly used for model castings, can have various compositions; https://www.sputtertargets.net/blog/an-introduction-to-white-metals.html#:~:text=In%20its%20most%20basic%20form,silverware%2C%20ornaments%2C%20or%20novelties.
So, the next problem is knowing which white metal your tank tracks are made of. In order to avoid lead toxicity, my guess is Bismuth-Tin and/or Antimony alloys are used, but I don’t know. This is a deep rabbit hole, one with few definite answers unless you have played in this arena before. There are a large number of patina formulas out there, if you really want to pursue this, I’d recommend obtaining a book on metal patina finishes. Then there is the problem of obtaining the raw chemicals, which is why there are many commercially available, pre-made patina solutions.
Just to illustrate my point about alchemy, the following recipe for a dark brown patina on bronze, taken from the 1914 (“new and revised” edition) of Henley’s Twentieth Century Book of Formulas is as follows, go ahead, just try to translate into modern chemical nomenclature;
I.—A dark tint may be obtained by cleaning the object and applying a coat of hydrosulphate of ammonia; then, after drying it, by rubbing with a brush smeared with red chalk and plumbago. The copper may also be moistened with a dilute solution of chloride of platina and warmed slightly, or still by plunging it in a warm solution of the hydrochlorate of antimony. For the verde antique a solution is recommended composed of 200 grams of acetic acid of 8° strength, the same quantity of common vinegar, 30 parts, by weight, of carbonate of ammonia; 10 parts, by weight, of sea salt; with the same quantities of cream of tartar and acetate of copper and a little water. To obtain the bronze of medals several processes afford a selection: For example, the piece may be dipped in a bath consisting of equal parts of the perchloride and the sesquiazotate of iron, warming to the evaporation of the liquid, and rubbing with a waxed brush.
The bottom line is that a lot of metal sulfides are black or dark brown, especially base metals like Bismuth, Antimony, Tin and Lead. Note all the sulfides in the constituents of “Liver of Sulfur”, you are simply replacing the Potassium ions in solution with less reactive base metal ions, forming insoluble metal sulfides. Just remember, Liver of Sulfur is highly corrosive, toxic and smells really bad, not the kind of stuff your better half wants you playing with in the kitchen. 
This is why you may want to find safer, less toxic ways to do this procedure.
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I think everyone is after a cheeper solution, then the expensive, one use, shop jars variety.
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My solution to not buying the expensive one shot bottles of MiG and AK stuff was to buy this:
It was like $80 but much cheaper than the small bottles and I have several years supply. It works on all the different metal tracks I have used it on. Gives a great dark brown \ black patina.
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Can also be found in smaller bottles sold to blacken “cane” material used by stained-glass crafters. Look for it in the same section of the big-box craft stores that sell the colored glass, etc. Can also be found on Amazon by searching for stained glass supplies.
An alternative (although not cheaper than the proprietary modeling stuff but often more readily available) are the solutions sold for “cold bluing” on firearms. (This is also sold in a formula to blacken aluminum allow parts.) In the US, Birchwood Casey is the most common brand.
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Exactly. But if people ask for the active ingredients, this implies wanting to compound your own formula. This isn’t like baking cookies here, these are hazardous materials. All patina solutions are “one use”, as soon as the sulfide ions (in this case) are depleted. As I stated above, there are many commercially available products you can buy, in quantities up to 55-gallon drums, no one needs to buy tiny little jars of model shop stuff. Note that no ingredients are listed, (I looked at the Jax product page). Secret formulas…
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I don’t build much armor, so maybe this is a dumb question: Why not just paint them? It’s not like the treads are going to see much wear.
As Paska says, the stuff in these solutions is nasty! I know because I’ve used some of them on black powder firearm parts—after hours in the chem lab fume hood where I used to work. NOT something for the home kitchen or workshop, IMHO.
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There is a safety data sheet listing hazardous ingredients:
- Nitric Acid (Solution,less than 65%) 0.5 - 5%
- Selenious Acid 0.5-5%
- Copper Sulfate Between 0.5% and 13%
- The remaining components are not classified as hazardous in their existing concentrations.
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This is pretty much what I do now - I just paint the tracks. I found that I was buffing and masking to create the bare metal areas, and that first giving them a chemical treatment was a wasted step. I wound up painting over all of the chemically colored areas anyway.
However, I did chemically color metal link-to-link track sets for years, so I appreciate why some modelers want to do this.
These T-44 tracks are indy-link metal T-34 tracks from Master Club. The bare metal wear areas were done by buffing the metal with 4x0 steel wool, then masking with strips if common blue painter’s tape. The rest of the finish is a combination of airbrushed colors and dry artist pigments. The last step was to lightly buff the outside high contact surfaces with the same 4x0 steel wool to reveal bare metal on those spots.
For plastic tracks, I pretty much do the same process except instead of buffing with the steel wool, I start off painting with black followed by a bright silver on the interior bare wear areas and then mask those off the same way.
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That’s what I do,prime,paint and weather them the same as plastic,3D,and resin ones,works for me.
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Thanks for posting the SDS, I didn’t even think about looking for one, which is rather ironic, since I used to be in charge of the SDS program for our company. 
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