Older steel tube weaver scopes. What have You used that works good to touch up blueing?

Brownells Oxpho Blue. Rub it down with 0000 steel wool to prepare the surface. Heat to about 120F or to just hot enough to hold on to. Pour some bluing into a small container I save plastic cups from individual Jello servings). Dip some 0000 in the liquid and rub it in. Make sure the metal is WET all over, and rub for about a minute. Wipe down with cotton rag or paper towel. When dry, rub again with fresh 0000.

Use a hair dryer to heat it up.

I went the Oxpho route with an old steel Kahles I had, looked great when I was done.

About 4 months later it had started to fade to a greenish color.