doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com French gray finish...

Can anybody tell me the process? I have heard naval jelly, toilet bowl cleaner, etc.

What do you do and how do you do it?

Thanks in advance.

I've played with Oxpho Blue to "age" small parts. It is pretty controllable if you're careful. You can experiment on a bolt head.

Phosphoric acid, which is likely the key ingredient in the products you mentioned, will leave a slightly dull, pale gray finish that is fairly durable and rust resistant (certainly more so than any blue job). I've used it for other applications, swabbing the acid on and leaving it for about five minutes before rinsing and drying. Whether or not this is the process that the gunmakers use, I cannot say.

As an aside, the finish on military guns used to be a phosphate derivative. Oxpho Blue - I've always wondered if it isn't some kissing cousin to the phosphate process.

One version of "French Grey" is the case hardening process without the "stuff" in the quench to form the surface layers that yield the colors for case color. I tend to think this is original French Grey, but could be wrong. The high carbon content of the case layer makes for a very corrosion resistant surface; the corrosion resistance of steel being highly correlated to increasing carbon content.

Of the various processes explained on this forum by some very well read members, the one Rocketman mentioned above, I also believe it may be the core traditional method.

I generally use acid for this finish, esp for engraved guns where the relief is frosted and the high points are polished. The process brought up by Rocketman is interesting, I have quite a few turn of the century books on heat treatment and case hardening of steels. Many of them mention that if you want bright case hardened parts, ass sulfuric acid to the quench bath.

There are acids and there are acids. Some are stronger than others and will do some serious damage. I have learned that many of the common toilet bowl cleaners contain hydrochloric acid, generally in the 10% + concentration range. That will do more that simply etch to a frosted finish if the part is left too long. Timing is key. I read in some old gunsmith book, I'll have to go into the upstairs room to see which one, I don't remember just now, that phosphoric acid is preferred. It seems to be more forgiving than other acids as regards time, and the finish is also more what you are likely looking for, more of a soft frosted look. There is a government on-line site for a huge Household Products Database at:

http://householdproducts.nlm.nih.gov/index.htm

that will tell you many common products containing hydrochloric, phosphoric, and/or whatever you are looking for, a very good reference. Search for rust removers. Blueing is a form of rust. I found that Home Depot sells a Behr product called a concrete cleaner and rust remover that contains 40% phosphoric acid. I cut it back to 10% or so and use that. In my judgement, it gives a better finish than does the hydrochloric acid products. Coca Cola also contains phosphoric acid, don't spill Coke on your nicely blued barrels, it'll take the blue right off.

Naval Jelly contains some 35%-40% phosphoric acid. It will certainly work, I think that’s too strong for most use.

Try the above database, you may already have some product around that will do what you need. Just be careful with any acid, wear protective gloves, clothing, and eye protection. Better safe than sorry. Many household type products can be VERY dangerous.

A much safer alternative to hydrochloric, sulphuric acid etc is boric acid, often sold as a pharmaceutical, I believe it forms part of many skin preparations. It is not expensive, about £5 for 500gms, and made up as a saturated solution, about 5-7% solution in distilled water at 70-80 C, it lightly etches steel to give a silk grey finish over an hour or two depending on temperature.
It also removes rust and other oxide finishes very gently but completely. I have used it several times to remove the thin brown rust coating on lock plates and actions and although the finish is a bit drab for my taste, it may be what you are looking for. There doesn't appear to be any after rusting, a problem with many stronger acids.
Used on Damascus barrels it will produce a differential etching of the steel and iron to prepare the barrels for browning. I prepare all my damascus barrels (thoroughly plugged of course!) and damascus snapcaps with this solution. After degreasing with 'whiting' I lay the items in 70-80C solution for anything from 30 min to 3 hours depending on the finish I require.
The carbon in the steel remains on the etched surface and just needs wiping off before thorough rinsing and then straight into the browning process.
It is pretty safe on one's skin although I always wear light gloves as it tends to dry one's skin out.

Toby:

Thank you for the information on Boric acid. I have not heard of its use before and will give it a try.

Much obliged,

Glenn

thank you for all of your replies.