doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Rust Vs. Salt Blue (SxS Reblacken)

Temper colors from an older Machinery's Handbook, all in Fahrenheit;
430° = Very Pale Yellow
440° = Light Yellow
450° = Pale Straw Yellow
470° = Deep Straw Yellow
490° = Yellow-Brown
500° = Brown-Yellow
510° = Spotted Red-Brown
520° = Brown-Purple
530° = Light Purple
540° = Full Purple
550° = Dark Purple
560° = Full Blue
570° = Dark Blue
Note that as the heat raises most of these changes are very subtle & requires a very experienced eye for "Precision" control.
It should also be noted these colors were cited using plain carbon steels, some alloys will cause variations.

The 'molten salt' process is 'Nitre Blue' most commonly done w/Potassium Nitrate (sometimes mixed with Sodium Nitrate I've read),,but you can do it with other chemical salt compounds as well. I've gotten OK results with Ammonium Nitrate. (Don't know anything about using common NaCl table salt)

Winchesters recipe stated they added manganese dioxide I think for some reason (more blue color?, lower melting temp?). Seems to work fine w/o it though.
Used generaly for small parts, but a receiver can be done in a container large enough. Winchester did their receivers by Carbonia Blue system.

Depending on the temp you bring it up to, and sometimes depending on the alloy of the steel, you will get the different colors you want. Anywhere from 'Luger straw' to gloss black if everything is right. It's a tempering/annealing process as well as coloring.

A little bit of experimentation is in order at times when doing odd parts from different guns but the general guide lines of temps for the deep blue colors hold true. If you go too far, you have to strip the piece of blue and recolor it.

The process can also be used for tempering newly made springs. They temper at a color range that will generally impart that bright fire blue color, hense the name sometimes used...spring temper blue.
If you take it up to around 800F give or take, and this is where it really takes some experimentation, you can get a charcoal black gloss color.

Keep any water far, far away from the stuff and wear all necessary safety clothing and gear when using it. There's no escaping the burns from molten liquid salts @ 400 to 800F that splash onto you.

Thank you, Kutter. Guess I assumed NaCl or read it by someone else. The issue would be a fluid that was stable at the right temperature and with the right heat transfer rate in which to immerse the part (with a bit of oxygen present), would it not? The nitrates are powerful oxidizers, so they would have plenty of oxygen available. Come to think of it, maybe that is necessary to get the oxide film?

How do you do carbona blue?

Rocketman,

This was copied from the S&W forum!

"Carbona bluing is not simply a heat process.
The ovens are heated, PRESSURIZED, and the atmosphere is a CARBON-rich (hence the name Carbona) environment via various forms of charcoal.
In effect, you could say the gun is "plated" with carbon via heat and pressure.

You can see a pic of the ovens in Smith & Wesson, Images of America by Jinks and Krein."

Lee Jarrett

binko