The only salts I have ever used is Oxynate #7 from Brownells. I've had good success with it but my last 2 batches didn't seem to last very long. (That's kind of a seperate issue). They are getting a little spendy too. Where else can you buy salts. I've heard of a couple different salts but can't find where to but them. Is there a less expensive option?

In the past I mixed my own. You can go to a pool supply house and buy caustic soda flakes (sodium hydroxide) and ammonia nitrate (the fertilizer) and mix them if I remember correctly 2 to 1 respectively. They blue very well and last, for a fraction of the price. I'd double check on the ratio first though.

Problem with mixing your own is I can never find a true up to date formula.

Dulite.com is a good plan B

Here is one formula:

http://www.knivesby.com/blueingsalts.html

Thanks Canuck
The ones I've found were Mercury based spirit niter nasty stuff i had no intention of using.