I would give the man my formula that I have used for the last 35 years but I doubt he could buy all the chemicals,, so for what he wants, the BLUE wonder BLUEING system is about the best for an amature..I am sure he doesnt want to build heating tanks and go to the expense of the proper chemicals to do a professional job..
He could probably Use several other Blueing products such as Birchwood Casey cold blue or 44/40 instant blue from Brownells..
Anyway here is my (along with many other gunsmiths) formula for hot water blueing.
1/4 oz potassium nitrate
1/4 oz sodium nitrate
1/2 oz of bichloride mercury---this is hard to get
1/2 oz of potassium chlorate.
Mix with 10 oz of Hot 150 degree water..