I use a product from Caswell called Black Oxide. Caswell Inc. - Black Oxide Kit
It works good and fast, low toxicity I think also.
A bit expensive but a little goes a long way.
Hey Folks
These are recommendations I received across the street and down the block.
Lehigh safety boots and/or Iron Age.
Both have metatarsal options and real stores to help you fit the shoe to your foot.
Bart