My friend who does some very nice rust blueing recently got some charcoal to use for blueing parts.
Has anybody had experience with this and if so what is the process?

I do the process occasionally. It is very labor intensive and you can get a similar color other ways. A very good article was written in "gunmaker" the ACGG publication by Dave Norin. I believe the temp. is 800 degrees if memory serves. The freshly polished and degreased item is placed in a sealed crucible and brought up to temp., Brought out after sometime and rubbed while hot with lime and a cotton cloth, repeat until desired color is achieved. High lust polish for the best results. It is pretty and durable but not one of those jobs I personally enjoy much.

How do I go about getting a copy of that article for my friend? I understand early Colt pistols were done this way.

All of the back issues have been digitized(thank you Dennis Daigger) and a CD can purchased from the guild here:

https://www.acgg.org/index.php/contact-acgg/central-office.html

The charcoal blue process used by Colt was called the Carbona Blue Process. It is very different from the use of charcoal to produce a relatively fragile heat blue, which is more along the lines of what you get when you are tempering steel after hardening.

Carbonia blue, furnace blue? I had several parts finished by Classic guns Inc. back in the day using this process. The color of the finished parts was a very deep and shiny black, very attractive. The parts were highly polished and looked like mirrors. With all that said...I saw very little difference in these parts compared to other parts that I had blacked using good quality bluing salts. Durability of the finish also goes in favor of high quality hot blue using high quality fresh salts. The carbonia blue was also much more expensive.

Dustin

Dustin is correct. Carbonia blue was a very similar process to the Carbona Blue used by Colt.The slight difference in spelling indicates that the Carbonia process was a proprietary process used by Smith & Wesson.

When you see an old bluing job that has areas where the blue looks as if it has flaked off rather than simply wore thin, that is a good indicator that you are looking at a Carbonia or Carbona blue.

Carbona blue I have had John do for me in the past as well. The original process for Carbona involved a rotary gas furnace and oil as well as charcoal. It was a patented process develop by the American Gas Furnace co. I am not sure what John's process is. It gives a different color than true charcoal blue, more of a blue/black but very attractive. Carbona and charcoal are two different finishes but both utilize bone charcoal, only carbona uses oil.

Charcoal bluing as practiced by Victorian gun makers and still used today by the original Artisans that perfected this method who where clockmakers. If you take a close look at the screw heads and other steel parts on a vintage European clock or pocket watch they have a polish and depth of colour that is a truly striking blue indeed.
It only uses one ingredient finely powdered charcoal and an Iron pan with a very controllable but small heat source applied to the pan. Each screw or part is polished to a mirror finish then covered with charcoal powder then the temperature is very slowly increased the slower the better. Each part is removed periodically to let the oxygen in the air cause the oxide layer to increase in thickness on the surface of the item being blued also any corrections in the mirror finish is done, with the finest blue colouring arriving at about 570 degrees F.
It is an Artisan skill which I have not mastered to the point that all my clock parts do not finish with the identical blue colour but are close enough, been trying to get it right for a lot of years now and running out of practice time.

I am familiar with cold rust blue (barrels), nitre blue (pins and small fittings, and carbon blacking (trigger guards usually). I am a bit fuzzy on the distinction between carbonia blueing and carbon blacking. Same, similar, totally different ?

The process described by Damascus is essentially identical to one found in an old Machinery's Handbook I have with a 1946 copyright date. They recommend putting the part in the charcoal, in an iron pot & then stirring while bringing up to heat. They also mention that sand or wood ashes can be used for a lighter color, but for the darker color pulverized charcoal should be used. No mention is made of sealing the container or that the charcoal should be bone derived, seems to indicate ordinary wood charcoal.

The American Gas Furnace process is also mentioned in this book & it does specify charred bone to be used. Also a liquid is injected during the tumbling process. What this liquid is, is not specified, probably because it was a patented process.

It is said that the liquid used in the American Gas Furnace or Carbonia process was a mixture of several oils including sperm whale oil and fish oil. It's reported that because of that, the process stunk to high heaven. It was a proprietary process that was a trade secret owned by Smith & Wesson, but Turnbull and others claim to be able to reproduce it. The Carbona process used by Colt reportedly involved heating gun parts in charcoal and rubbing the heated steel with rags soaked in fish oil. This was said to smell pretty strong too.

My tried and tested heat bluing of gun pins (screws) giving a good deep lasting blue colour is.
Firstly heat the screw to the correct bluing temperature 570F or the colour you want by eye, slowly to increase the oxide thickness. To halt the colouring process drop the screw in oil. This is where we modern folks have to substitute something for the Whale oil that gave the best colour in days gone by.
Over the years I have found three substitutes that work extremely well, though all require some heating to make them a liquid. My preferred oil is "Lard" second is "butter" the final one is "Tallow" though I do not like the smell Tallow gives off when the hot metal is dropped in.
As you can see they are all animal derived oils leaving Whales to get on with their lives.

I heat blue in Niter salts, very different from charcoal blue which is really a deep black when done correctly. My heat blue comes out more of a peacock blue.

What temp are you nitre bluing too?
Higher temps will get darker colors.

I niter blue right around 575 F. I have never been able to get a deep black with niter salts.

When I heat blue using a torch, my quenching oil of choice is olive oil. I can’t tell the difference in finished color between using olive oil or brownells quenching oil

Larry Schuknecht of Dutchman Woodworks does a nice job of blacking using niter salts. Very black, smooth finish. Even he admits though, it’s not a very durable finish. I believe a lot of early American SxS guns had their furniture finished using the niter method. .

The target temp for jet black with nitre salts is 830 degrees. But i can usually get very good color at around 750.

LeFusil, Is the heat blue durable? Enough for a trigger guard? I have one to blue. Interested as the heat blue method doesn't appear to take a lot of special ingredients!

Thanks!

It doesn't take a lot of special ingredients, but it takes a great deal of caution. Molten potassium nitrate at over 700 degrees can cause some very severe burns. Leather gloves, safety glasses, and a full face shield are good precautions. Heating a pot of previously melted salts can erupt violently as the bottom melts and the top is crusted solidly over. For this reason, put a bolt or lag screw in your pot before it cools, and unscrew it to provide a pressure relief hole when re-melting. Heat blue is not as durable as hot salts bluing or rust blue, but it is fairly durable, and a good method for screws and other small parts that won't have their temper changed adversely.

If you want easy with a minimum amount of set up buy some Mark Lee's express blue. Follow the directions exactly. Polish to a very high luster and you will be happy.

Thanks SKB, looked at the product and the instructions, I'll try that! Thanks Keith for the info, I think I'll let that alone!

Once you use Mark Lees, you will not go back to traditional rust bluing.

I use both but I like having a large bag of tricks. Been mixing my own browning solution for years. Just mixed up a blue solution as well. Does anyone have an express blue formula you like?

I wasn't trying to discourage you from trying the nitre bluing process. It is relatively cheap, easy, and has it's place for some parts. I just wanted you to be aware that there are some potential hazards that you can eliminate rather than rushing in and getting burned.

Keith, No worries, I'm not put off by the process. I don't want to invest that much into what would likely be a one off! I carved a stock for this gun long ago and had the original PG trigger guard straightened out for a long time. Finally got a long tang guard in the white, fitted it and it looks a bit odd now. I'd like to get it blued. There is no local 'smith that has a set of tanks that could toss it in with the next run and I don't want to send it off. So thought I'd try it myself. The gun is not a showpiece, Ithaca/SKB 100 that I use alot. Thanks again!

The higher temps work well for black. Ran a few screws yesterday and they came out nicely. Thanks for the tip.


Any one have a Belgium blue formula they like? I noticed Angier's denotes several of the formulas he lists as express blue.

SKB. Yes I have an express rust bluing formula for gun barrels that was once used extensively on this side of the pond, from start to finish it takes about an hour and a half giving a very fine rich deep dark blue colour. It fell out of favour due to its cost and toxicity with the formula being a closely guarded secret in the trade, I still use it myself for the occasional piece of work.
Quite surprisingly it was developed by the notable American Gunsmith, though Angier does mention it in passing in his book but may be there was a little rivalry involved because he does not elaborate much on the how and why.