I don't know if this is a daft question or not. When I order mild steel it often appears with a kind of black coating or oily surface. What's the best way to remove this for painting?(Particulary for larger items)
The black coating you are refering to is probably scale from hot rolling the steel. I use citric acid or cubitron flap or fibre discs to remove it after degreasing with brake cleaner. I used to use hydrochloric acid but have been warned about corrosion risks so no longer do that even though it's fast.
