I live in the country & get my water from a natural spring. I very quickly found it was not suitable for the boiling tank in rust bluing. I made several attempts on a set of barrels & each time they would come out with a red tinge. I then went & picked up some "Drug Store" water & repeated the very same process with excellent results. Because mine won't work doesn't mean no-one elses will & because one person is able to use tap water likewise doesn't mean everyone can. It all Depends on what's in that source of water.
I have done one job using steam & it worked fine. A co-worker of mine had a large knife which had belonged to his father that originally had a blued blade that had worn off over the years. He asked me coud I blue it for him without taking the handles off. I told him I would try & see if I could. After rusting the blade I put a tea kettle on & turned the heat up enough to get a good steaming at the spout & simply held the blade in this until it turned a good color & carded. I of course had to repeat the process several times to get the desired results.
I do recall having read where many of the world's armories when rust bluing was still being used by them had steam Rooms where large numbers of barrels etc could be hung & steamed at once. Some of the larger commercial factories may well have done this as well. In fact this was what gave me the idea to try steam on that knife.
