Most any of the Ant & Roach killers in powder forms sold in places like WalMart and DIY stores are Boric acid.
Big plastic squeeze bottles with a narrow nozzle on them for getting at them kritters! Cheap too.
I use the stuff as a heat scale shield when making some small tools and such.
Mix a paste of it up w/alcohol. Coat the tool with it. Light the gob up and the alcohol burns off leaving a very brittle but airtight shell around the tool/part.
Bring it up to temp. When quenched, the shell disintegrates leaving the nice, bright and clean piece ready for tempering.
Sorry for the thread drift.
Muriadic or Nitric acid in very dilute soln (1 or 2 tbs /per Qt water) work well to bring out a grey finish. Parts usually need to be aggitated with a small brush with the soln while they are submersed in it.
Room temp!, don't try and hurry it along w/ any heat.
Even up any dark areas w/ 0000 steel wool or better I find those PinkPearl erasers work great. They come in different grits too.
Belgian Brownings color very quickly using Nitric and this method.
If you are Express Blueing (Quick Rust),,placing the parts in the boiling water tank and occasionally plucking them out and carding them will give you a pretty easy and nice grey finish.
Don't coat the parts with any of the bluing soln,,they just get effected by the residual soln and chemicals from the Bluing you are doing that is in the water.
They come out nice and even in my experience. Maybe because the chemicals are in such low % in the water.
Just another of the many ways to get a grey finish.
