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Compounds in Black Oxide metal blackening solutions

Q. I am fairly confident I know how black solutions work but an Old gunsmith mate of mine he died in 1974 used a mixture of sodium nitrate ⇦ this on Amazon [affil link] , caustic soda [caustic soda beads in bulk on Amazon [affil links] , tri sodium phosphate (1 lb 1 oz per gallon) and a very small amount of common table salt (3 ozs per gallon).

Any idea what the trisodium phosphate ⇦ this on eBay or Amazon [affil links] was for? I am thinking it may just be a cleaning agent.
What was the salt for? I am thinking it may be some sort of a catalyst.

I was going to make up a batch but you cannot buy either sodium or ammonium nitrate. We have gone mad in Australia our pollies think there is a terrorist hiding behind every tree, I cannot even buy the stuff legitimately. Another recipe is ammonium nitrate and sodium hydroxide and water it gives off considerable amounts of ammonium gas.
One of the commercial solutions used to have problem of purples when used with stainless steel tanks? What causes this and how can it be avoided
Thank You.

Vaughn Gunthorpe
Hobby - Townsville Qld Australia
June 1, 2010

A. Hi Vaughn.
Same problem here in Sydney.
I have been doing a lot of reading and a crash course in chemistry as well, And it seems you can recrystallize sodium carbonate ⇦ this on eBay or Amazon] to Sodium Nitrate with Nitric Acid !
I will be attempting this in the near future as I need to restore my 308 Winchester.
Now for the Sodium Carbonate I found they sell it at Woolworths , Check out the Lectric soda Crystals 650 g Net and Google Sodium Carbonate and Nitric acid .

Lenny Sch
- Sydney, Australia
June 5, 2010

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Well before you poison or blow yourselves up try this. If you go down to the food store you can buy sodium hydroxide, it's called lye. It's used for cleaning and clearing clogs in your toilet. Even if the water does go the wrong way about when you flush it. If you're really cheap then I suggest you go down to the place that sells cleaning supplies to the pig farms and dairies they will sell you sodium hydroxide by the drum. As far as the niters the best is sodium nitrate and its surprisingly easy to buy. You can buy sodium nitrate fertilizer at the lawn and garden place or you can buy it at the butchers supply (or abettors I believe you people call it). It's used as a preservative in sausage and meats. If it was me I would go down to a chemical supply place; they know as well as I do that it is a very poor explosive and as soon as they feel you are going to do something silly with it and ruin your wife's stove and floor with it they will probably just smile and sell it to you. I have to get a permit to buy both chemicals here in Canada but the reason for that is that it's caustic and the permit is to store it within city limits. There really is no practical explosive use for either chemical. Even ammonium nitrate is easily obtainable at any lawn and garden store but I wouldn't recommend it as a chemical for bluing even though it can be used. But, if you happen to be REALLY CHEAP, polish your parts and take them to your local gunsmith. He will dip them in his tank for you for about $40 for every 20 pounds of parts you bring him.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
June 10, 2010

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June 18, 2010

Hi Rod
Thanks for the info with Butchers using it as a preservative!
The Government has gone anti Nitrate here in Australia and it seems we are all suspected terrorists, it is near impossible to buy nitrates in any form from anywhere.

All the lawn and garden supply places now sell inert alternatives as fertilizers and if there is any nitrates in them there is so much other crap mixed in as well that it makes them useless for our application!

Most of the Gun shops here have gone very commercialized and don't sell D-I-Y products; sure, you can buy the gun blue in tubes and small bottles that you rub on, but most forums say that it rubs off nearly as quickly as it took to put on !

The Typical Gun shop here will try and sell you a new gun or part to replace the part we only need to re-blacken.

As for gunsmiths they are hard to find here, there aren't too many about and all our gun parts have to be sent via special couriers because it's illegal to send any other way !

Lenny Sch
- Sydney, Australia