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.

Do these acids increase the C content of the steel? I doubt that they do, but I could be wrong. I think that they just etch on the surface not necessarily increasing the strenght.
I also thought that the French Grey finish is obtained by removing the colours of the case hardening process.

That's the way I've always used French Gray, after case hardening.
This custom Garbi 20 ga. was pack hardened by Doug Turnbull then the colors removed with a soft mechanical abrasion technique leaving the glass hard skin. Just coloring the metal (or removing the color) without the hardness would be suspect (to me) as far as corrosion resistance(??)
Years ago I "grayed" one non-hardened action because the engraver insisted, but that action did not need hardness, and I laquered over the "gray" to prevent rust. It has held up over the years but I wouldn't do it that way again and I've encouraged the client to revisit the metal finish.

French Grey or just grey finish?
As I remember Mr.Gaddy told French Grey was allmost the same case coloring process, but no shields over metal parts and quench liquid was Calcium Chloride(??)water solution.

Acid does not add any carbon to the steel. It only imparts an etched surface. Highly polished is to shiny for most shooters' taste. A mechanical or acid etch of very fine "grain" produces a more grey matt appearance. Case hardening does not automatically produce colors. However, as said above, removal of the color layer will produce a grey base metal.

Case hardening in itself does not impart colors. It is the impurities imparted by "the pack" which results in coloring the metal. Case hardening is done every day to all sorts of tools and parts. To simply case hardened metal, there are various compounds available. None of them imparts a color. Including Kasenit and Cherry Red:

http://www.midwayusa.com/viewProduct/?productNumber=119479
http://www.youtube.com/watch?v=9tlsq2ESQz0

Early gun makers would heat a part and then quench in linseed oil, which imparted colors, see "The Gunsmith of Williamsburg" with Wallace Gusler. http://www.armoryhill.com/review_gusler.html

Here you can see receivers being packed in charcoal at the Marlin factory prior to heating.


The charcoal imparts carbon, ie, acts as the carburizing agent. In adding carbon to iron, we produce steel. This is from Oscar's articles in DGJ showing a scanning electron microscope image of the surface after case hardening with charcoal.
http://www.doublegunshop.com/doublegunjournal_v7i4_9.htm


This surface color is only a few microns deep. It can easily be removed. It happens to most guns over the years just by contact with the hands. Ken Hurst simply uses some toilet bowl cleaner and a scotch-brite pad to achieve a french grey after the part has been case color hardened.

Pete

Pete, it's not colors only, it's protection from corrosion. If you delete case colors, the surface of steel will be open for corrosion. That's why surface has to be sprayed with trasparent laquer. The idea of French grey - surface is protected from corrosion just after quenching in water solution.
I heard gunsmiths in Ferlach use argentation to imitate and to "restore" French grey finish with yellowy patina.

From J.V. Howe (of Griffin & Howe), Formula No. 27, a GRAY color on steel is achieved by immersing the work in a heated solution of:
10 gr. (avoir.) Antimony Chlorid
10 gr. gallic acid
400 gr. ferric chlorid
150 cc. distilled water
The first color to appear is pale blue, then darker blues to purple, and finally to gray. If immersed long enough the metal will assume the gray color.The intermediate colors are better produced when the solution is cold. The above is considered one of the "bronzing solutions."

Geno, per a discussion with Dr. Gaddy, the case color film is very thin and loosely bound. It provides very little corrosion protection; the bulk of corrosion protection comes from the high carbon content of the case "skin." The use of a clear coat (wax/drying oil/lacquor/poly/etc.)is for abrasion protection for the color layer. As above, there are many ways to make a grey finish on steel.