I would like to start with a lesson I learned this week on what I believe to be the most basic and easy-to-apply steel finish, which is Penetrol. Penetrol was originally made as an additive, or “conditioner” for oil based paints, I am sure of the industrial kind, but I think of it like a lindseed oil or fine arts painters medium that makes the paint more fluid and easier to work with. Somewhere along the way it was discovered that the Penetrol by itself made an excellent finish or sealant for steel, and a miracle rust stopper. The Penetrol is applied only as one coat and actually is absorbed into the pores of the steel, which makes it a permanent sealant that should not need reapplication.
The times that we use Penetrol in our shop is when we want to have a clear finish, usually over Hot Rolled Steel. Penetrol is especially cool over industrial steel parts like flat bar, heavy gauge plate, tube or channel steel, where the millscale is raised and rust is starting to show. The result is a subtle satin sheen over raw, honest steel.
Where Penetrol is not ideal is if you have shiny spots or grinding, scratches, seams, or any other parts in the steel you want to hide. These could be pretreated with a patina to blacken, but really, if you are trying to cover up things, this finish is not for you. I am also not sure how this works in exterior applications. I am going to google that or ask one of my experts….