On Wed, 4 Jan 2006 17:47:17 -0700, "JensenC" farview at frontier dot
net wrote:

I'm about to make some welded square tube picture frames and have been
looking into various blueing products. 44/40 runs about $8.50 for 2 oz.
Oxpho-blue runs about $9.50 for 4 oz. Van's Instant is about $10 for 4 oz.
Hoppes runs about 9$ for 4 oz.

I'm wondering what folks here have found to work best on mild steel. Any
hints or tricks?

http://www.caswellplating.com/kits/black.htm

Black oxide concentrate to make up 1.25 gallon of solution $22.00.
or $33.00 for a quart of concentrate that makes up 2.5 gallons of
working soup.

Unlike Oxpho blue and others which must be wiped on, you can immerse
parts in the Caswell stuff. It does not need to be heated. It
makes a nice dense black. It isn't as durable as hot salts
processes, but it's very easy to use and it looks nice. I've
blackened a number of small parts in a quart of it I mixed up probably
5 years ago. It still works fine.

The penetrating sealer works well, but I think it's just linseed oil
and solvent.