I am curious what brand of cold blue do you recommend for touch up. Also what procedure do you use.

Be sure it is Cold Blue that you want. It is better to touch-up Rust Blue using weaker solutions (slow build-up, repeated applications) and then steaming over a pot on the stove with a foil funnel. (Or other steam source) This goes double for Damascus and Twist tubes.

Cold blue usually has Copper Sulfate in it, it actually leaves a coating. It's your decision, Oxpho-Blue from Brownell's is my choice, available in both liquid or paste.

Regards
Ken

I agree with Ken61 about Oxpho-Blue.
Mike

Brownell's Oxpho-blue.

Oxpho is really the best cold blue out there. The trick to any cold blue is making sure the surface is CLEAN befor every application.

Another point about methodology. If using liquid, never stick a used swab/brush, etc. back into the bottle. I always pour a small amount out to dip into. It contaminates very easily.

Regards
Ken

Thanks for the information. Oxpho-blue seems to be unamamusly recommended. I see there is also 4440 advertised.

What rust blue do you recommend, also Ken you stated a weaker solution?
Do you delute with distilled water? Applying multiplecoats before steaming, then card off with fine steel wool?

After cleaning as well as you can make a paste of lime & a bit of water, agricultural or builders lime will do.
Apply this paste to the surface & leave for a few hrs then clean off. That will suck up every last trace of oil.
O.M

First, a few points/questions. What are we "touching up"? Is it a small piece like a trigger guard? Is it a barrel? If a barrel, is it fluid steel or Damascus?

I make my own solutions, but I'm sure others here buy theirs, so I'm sure they can offer recommendations. Many are Aqua Regia type solutions that work fine, with care.

For tubes, the judgement call comes when trying to match dilution with existing coloring, as it's better to start weaker than stronger, as it's harder to blend a darker spot into lighter background. Application needs to be fairly precise, with little bleed-over which would darken lighter backgrounds. I use pointed swabs (make-up applicators) and small artists brushes. Sometimes I allow it to rust a few hours, other times I steam fairly quickly, all depending on darkness of background color. One application, then a steaming/carding. It's better to err on the side of lightness, as you can always repeat the process with stronger solution. If Damascus, you have to periodically have a light vinegar spot-etch, a very tricky business. At the end it's a process of blending, not only with Steel Wool, but with pumice paste on the end of a swab if necessary. Chalk paste makes a good final polish, but at that point it's a judgement call.

Cold Blue, in my experience, (which may differ from others) doesn't work on Damascus or Twist because you can't etch it to bring out contrast. If anyone has been successful, please post your results/procedures.

Yes, distilled or filtered rain water is used for dilution.

Regards
Ken

I am just touching up a few worn trigger guards and screws. Possibly a few nicks and thin spots on barrels. Thanks for sharing.