I have some metal parts on an old Mauser, bolt and bolt release spring, that turned dark copper.

I had them reblued, but they turn back to copper color after the process.

Any ideas?

You can rust blue them to turn them black.

Lightly sand them with 400 to 600 grit wet dry, then rust using commercial rust blue solution (available from Brownells). Boil in distilled water, card off loose rust, and repeat until you get the finish you want. Usually about 2 or 3 applications over a purple/gold hot blue will get it looking good.

dave

Thanks!

I don't know about the bluing salts that most folks use these days, but in 1959-60 when I was doing bluing with BluBlak salts, in many instances the purpulish toned work could be made to go black simply by adding enough salts (or decreasing the water content, or turning up the heat) to the mix to increase the temperature about 3 to 5 degrees and holding it there a while.

The method I used was to just let a bit of the water content boil off and decrease the rate at which it was replaced.

You used to see it on some Greener GP shot gun receivers here in England. It was said to be a combination of:

1) Low grade steel being finished with
2) Tired bluing salts being re-used once too often
3) At the WRONG temperature...

Came out a copper brown colour.

quote:

was doing bluing with BluBlak salts, in many instances the purpulish toned work could be made to go black simply by adding enough salts (or decreasing the water content, or turning up the heat) to the mix to increase the temperature about 3 to 5 degrees and holding it there a while.

That is what I did when I was bluing as a second job from my garage.

The purpleish color some parts take on over time is a result of nickel content in the steel. There's not much you can do except reblue, and then as you've seen it will turn purple again over time. Older Rugers are notorious for this.

When I had my HOT CAUSTIC blueing up and running at first I would get diffrent colors on some parts. Depended on alloy of steel or heat treat. If your useing the hot caustic blue system I found brownells oxynates "s" solved 99% of the plum and purple colors.

Bill Ruger paid for spectograph analysis of his parts to determine the cause of plum coloration in his investment cast parts. Silicate added to the molten alloy to better allow it to flow into the far reaches of the mold was determined to be the cause.

quote:

Originally posted by Toomany Tools:
The purpleish color some parts take on over time is a result of nickel content in the steel. There's not much you can do except reblue, and then as you've seen it will turn purple again over time. Older Rugers are notorious for this.