Hi Charlie.
Oil and boot polish for steel parts.very much a similar process to gun bluing I think,?
Never owned a gun so maybe I am wrong.
There are some good You tube videos on homeshop colour aluminum anodizing with safe working practises.
Avoid the H2SO4 acid, nasty stuff to have around with pets and kids.I use it very rarely for picking off the scale after brazing.
If needs be, then use the acid diluted about 20:1, add the acid to the water, not the other way round, in a strong glass container.
During mixing the diluted acid gets very hot.
Please be careful.
--
John
John Lindo