Stuff to turn machined parts black

[benmychree]

The cold blue products that I have tried seem to be a mixture of copper sulphate, a bit of acid and selenium; the copper sulphate plates copper onto the bare steel, and the selenium turns it black, a very thin coating of very limited durability. As Bill Hudson relates, any oil or fingerprint on the metal disrupts the bluing process with cold blue processes, that is the beauty of the hot blue process that I described, the parts do not have to be hardly cleaned at all, in fact a thin film of light oil can cover the whole part; when it is immersed in the niter, it visibly burns off with a glow, completely covered by the niter, which is a 50/50 mixture of sodium nitrate and potassium nitrate, and is the lowest melting point of any salt mixture; individually, they melt at over 1,000 deg F. at the mixture of 50/50 the temp. is less than half that, and will be a slush at under 300 F.
I was introduced to the bath when I was an apprentice, the company used it for a tempering bath for heat treating of tool steels, I accidently discovered that it would blue steel parts also, only several years ago I came across a article in American Machinist that further described the process in detail.

 

[aliva]

I second the Caswell product, been using it for a few years, good results

 

[MrWhoopee]

Here's a process you can try using commonly available ingredients. It does produce a true black oxide.

Quick rust bluing--- Back in black!

The black finish left by the Birchwood-Casey Super-blue just wasn't doing it for me this day. The photo misleads, making them look a b...

mypeculiarnature.blogspot.com

 

[SLK001]

Here's a video of a 1-hour rust bluing procedure using common household items. It also produces a true black oxide.

 

[Aaron_W]

Here's a process you can try using commonly available ingredients. It does produce a true black oxide.

Quick rust bluing--- Back in black!

The black finish left by the Birchwood-Casey Super-blue just wasn't doing it for me this day. The photo misleads, making them look a b...

mypeculiarnature.blogspot.com

I recently bought everything to try this out, but haven't had a chance to actually do it yet (need to finish the parts that need bluing). The price is right, just a few dollars of readily available household chemicals.

 

[finsruskw]

Wow!!
Everything one always wanted to know..…...

Thanks for the replies folks!
Some of these commercial products sound quite involved

 

[derfatdutchman]

For small steel parts you can also do a heat blue. Heat your part until it turns dark blue, when the color is reached dunk the part in oil.

 

[acruxksa]

Brownell's Oxpho Blue.

 

[TTD]

Brownell's Oxpho Blue.

^^^ This stuff if you’re going the cold blue route.

Although I personally prefer rust bluing myself (never tried hot salt bluing so can’t comment/compare), when it comes to cold blue, Oxpho-Blue (or “Black Chrome” as I call it) is definitely my favourite....and I’ve tried most of them out there. I find it is a bit more resilient & better looking than other cold blues I’ve tried ( Birchwood-Casey, Outers, Van’s etc) but at the end of the day it IS still a cold blue & as such won’t be as durable as other methods previously mentioned.

Unfortunately, Brownell’s won’t ship it to Canada anymore , so I have been quite hesitant about using the last 40-50 ml I have left

 

[acruxksa]

<snip>

Unfortunately, Brownell’s won’t ship it to Canada anymore , so I have been quite hesitant about using the last 40-50 ml I have left

I can't get it shipped to Alaska either, however, our local Cabela's stocks it, but it goes fast.