Formula for cold blackening / cold bluing / cold black oxide

A. Hi Antonis. Goran offers 3 cold-bluing formulas on the page you are viewing.

In addition to this cold bluing thread, we also have many other threads about blackening -- thread 11740, "Black oxide formula for Hot Blueing of Guns/Firearms" should help you with the hot black oxide formulas. But note that there is more to hot bluing than the formula, and that it is very dangerous due to the risk of this hot solution erupting (water instantly flashing to steam); use hot black oxide only with training, full protective equipment, and in a proper industrial setting. Good luck!

Regards,

A. Don't waste your time with a cold blueing formula ,consult a professional gunsmith or blacking factory to ensure you have a finish that is both aesthetically pleasing and fit for purpose for a working firearm. Cold blueing will never replace or come near in quality to that of a HOT bluing / blacking finish; rust bluing can produce a really beautiful finish and is easy to do but very time consuming -- for this reason the technique is in decline.

The cold blacking technique does not produce a finish that is hardy enough to withstand regular use and is therefore not worth the time or effort put into that particular method. A Hot aqueous solution of sodium hydroxide , sodium nitrate is easy to make up and produces a superior finish that can easily be achieved with the right tank and heating system. Research of the formulas used, not always shared, can be interesting and also very fulfilling.

Herters Belgian Blue


(affil links)

A. Hi John. We appended your inquiry to a thread which offers generic formulations for cold blackening solutions. Good luck with them!

Also, there are vendors who sell in quantity, presumably at lower prices if you want to consider that option. Patents are public info and very easy to access these days :-)

Regards,

A. Hot aqueous solution 5 lbs Sodium hydroxide, 2 lbs potassium nitrate, 1 lb potassium nitrate, 17 oz sodium dichromate, add 4 litres water. Bring to boil at 110 °C add parts and watch them turn black, remove when happy with depth of colour.

Karl Sawyer
Owner black cat Blacking - Nottinghamshire uk
October 6, 2024

A. Hi Shayle. I have no experience with the best sequence for mixing those ingredients, but do have two comments. First, I'm not confident that good adhesion of the clearcoat is assured, because these formulations do tend to be quite smutty. Second, if you're going for blue, you might need highly polished metal; I believe that many blackening treatments tend to look a dark jewel blue color on highly polished metal but more of a matte black on rougher surfaces.

Luck & Regards,

A. Hi Abdullah. We appended your inquiry to a long thread about how to formulate and monitor home-brew cold bluing / cold blackening solutions.

But I don't think that's the heart of the problem. Rather, I think the question is whether cold blackening will suffice, and I don't think it will. I have seen and used these black-tipped screwdrivers, and although I haven't been involved in their finishing, I very seriously doubt that any high quality ones are cold blackened. I'm not even sure that they are hot black oxided, they might be black nickel or black chrome.

I don't think it would be a big deal to mask the shaft of chrome plated screwdrivers for subsequent processing -- a reusable PVC or silicone tube/straw with a centimeter of platers tape top and bottom seems like no big deal, and you have to mask near the tip regardless for a good demarcation line. Or you could do the black oxide tip first and mask it for the plating.

Luck & Regards,

A. Hi, D. You said "my preference", rather than "my requirement", so before talking about the formulation for room-temperature blackening, in fairness to you we should mention that it is generally less satisfactory than hot black oxide (but it is a lot safer). We have a quick Hot Black Oxide vs. Cold Blackening FAQ on line here.

The Metal Finishing Guidebook has a chapter with formulas for solutions for blackening and coloring metals. But better results will usually be obtained with proprietary blackening systems available from the suppliers listed in our directory or in the yellow pages.

For hobbyist level work, cold Gun Blue is readily available in small quantities. Good luck!

A. Hello, Sayid.

There are room temperature blackening solutions offered by EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser], Birchwood Technologies [a finishing.com supporting advertiser], and others. You'll finder deeper coverage in the Metal Finishing Guidebook ⇨

A. Hi, Mr. Yvas. Sorry that I don't know exact formulas, but some are in the MFG. People in the USA rarely make their own metal finishing chemicals anymore, so we tend to not have formulas in memory anymore; the people who know the formulations best are employed by the suppliers and can't reveal them.

However, as a start, I think room temperature blackening solutions are selenium and copper based. Searching patents or searching old journal articles from 20 or 30 years ago with surfacequery.com or scholar.google.com should be productive.

Personally, I find even the best room temperature blackening, developed over a period of decades, to not be the equal of hot black oxides. So I think your chances of developing your own room temperature blackening chemistry that you'll be fully satisfied with may be slim. But good luck.

A. Cold black for iron:
tannic acid ⇦ this on eBay or Amazon [affil links] .......20 gm
tartaric acid ⇦ this on eBay or Amazon [affil links] ......20 gm
water..............1 lit

Cold black II:
coper sulphate.......100 gm
selenic acid..........45 gm
nitric acid...........50 gm
water.................1 lit

A. We have an FAQ about Black Oxide and Cold Blackening, Muhammad. The Metal Finishing Guidebook includes a very good treatment of this subject. Missing will be the exact formulations of modern cold blackening solutions, however, as this is the proprietary knowledge of the companies who have invested in the experimentation. Cold blackening offers no corrosion resistance, although the wax or oil you may finish it off with will help a bit. Good luck.

A. We have an FAQ about Black Oxide on line here as a quick intro. After that, you could consult the Metal Finishing Guidebook. Then do a lit search and expired patent search. Best of luck with it.

A. Dear Suraj!
You can use next solution:

6 gms selenic acid
10 gms copper sulphate
4-6 ml nitric acid(1,34 gm/cm3)
1 lit water
20-25 °C temp.
according to Detnner/Elze: Handbuch der Galvanotecnik,1966.

A. Cold blue:
manganese nitrate...50 gm (up to 75gm)
copper nitrate ⇦ this on eBay or Amazon [affil links] .....50 gm
Water...............1 lit
50 °C temp.
Hope it helps and good luck!

A. Bernie

The formulation you have is about right for a "cold blue". As you would guess it gives a bluish finish of copper selenide. It is quick, easy, cheap and pretty useless for a working gun.
The durable finish you need comes from a molten caustic / nitrate bath. It is nasty, difficult, potentially dangerous and gives a superb finish.