Non-toxic bluing methods?

This is an unusual request: is there any way to blue gun barrels at production-scale volumes without using toxic materials (i.e. chlorinated substances)? I am interested in understanding if there are ways to reduce the environmental impact of standard hot bluing techniques. I know there are rusting techniques, but even these require some fairly nasty chemicals, yes? For instance, are there heat treatment methods that will accomplish the same oxidizing result? Or are there alternate alloys that don't require bluing?

Thanks in advance.

Your request is not the least bit unusual, Pat. Metal finishers have been living and breathing pollution control and toxics reduction for more that 30 years now to the virtual exclusion of anything else. The EPA has thrown money at beltway bandits to produce hundreds upon hundreds of duplicative studies on the subject. But to make any real progress in the pursuit you have to be pretty explicit about exactly what YOU mean by toxic materials, and reducing the environmental impact, and nasty chemicals.

What do you perceive as the environmental impact of hot bluing, in fairly specific terms so we can talk about it?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey