If you can get hold of a copy of 'firearm blueing and browning' by Angier ISBN 978-0-8117-0326-0 . There's a wealth of useful hints and information inside. A piece of denim from an old pair of jeans is ideal for removing most of the black oxide, you can never rub too deep. I use fine wool on any stubborn bits that are left.

Rust never sleeps !