[TheForge] Putting some blue color in iron

[H and P Foster]

One of my clients wants me to put some blue color in the chain I am making
for him to match some other material he has.  I have tried heating till I
see the blue color and then quenching in oil, but the color mostly goes away
by the time the piece cools.  What is the secret to getting a real nice blue
that I have seen on some knives etc, should I be quenching in some magic
brew or or or?

Thanks for any help

Harry Foster
Rusty Dog Forge
http://pages.infinit.net/rustydog/home.htm