O.K. everytime I go to do rust blueing the humidity falls out the bottom, so I built a damp box. It is 48" long x 11.5" high x one foot deep. Put a plastic window in it to keep an eye on things without opening the door.
I have not decided if I am going to use it vertical or horzonal as of yet...thinking vertical.
QUESTION: Am I trying to reach a certain tempeture with the humidity? I was thinking of puting in 2 light bulbs...one for the water to heat and the other just to add more heat. Would this be an advantage or a waste of time? Thanks!

My damp box is about 5'x1'x1'. I use an old crock pot in the bottom to provide heat and humidity. My objective is 85-90% and 85-90F. I have a light bulb(about 2' from the top of the box)on a rheostat that I use to control RH. If the RH starts getting too close to 100%, I increase temperature by brightening the bulb which inrease temp and therefore reduce RH. Conversely, I'll dim the bulb to reduce temp if the RH gets too low.

Thank you Mauser98, that was the kind of answer I was looking for. I'm going to get something to rust blue right if it's the last thing I do. I dont think there is any black magic to it but I've had a hell of a time trying it...Control from the box should be in my favor. Thank you again!

Thanks to Mauser98 he said he put a crock pot in his damp box. Told this to the wife and said hell that makes more sense then a lighted pan. Well she said she had a small one that came with the big crock pot when she bought it and never used it. It's mine now and pluged in the light and crock. My cheapy therometer ($3.00)with a test run shows 89 per cent humity and about 84 degrees with a 75 watt bulb...best I could get before box on humity was around 55. Got a new bottle of rust blue coming...will test it out then! Thanks!

Thanks for this very practical thread. I think I'll follow these ideas when I am ready to do my rust blue project on my Mannlicher Schoenauers.

Good luck.

Here's a shot of my damp box. I added a baffle above the crock pot to keep the risk of condensation on the lower ends of barrel from occuring. I use the little fan to keep the moist air moving.

Also, I top up the crock pot with hot water after each rusting cycle. It seems if the water gets too low, maintaing RH levels become more difficult.

Mauser98, Thank you for posting the picture! I was thinking of a cover over the top of the crock pot because I did get condensition in the window. Also the small fan would be a nice touch in keeping it all moving within the box...nice! I ran mine for a couple of hours and the small crock pot doesnt boil but put off a light vapor of steam, may have to go bigger. Had I just taken that weather course in gunsmithing school.