Just leave the parts in the boiling water for a few minutes till they are as hot as the water. Most 'cold rust solutions' don't work well as a 'hot rust solution'. Get one specificly designed for the task. When you figure the part(s) are as hot as they're going to get (doesn't take long really), take one at a time out, shake the excess water off, the rest should immediately evaporate if the part is hot enough. Compressed air helps to get water out of holes and crevices though I've never felt the need to use it. Make sure if you do you use an oil-less air compressor or one with a good clean oil trap filter on it for obvious reasons. With the water off, quickly and evenly apply the solution to the metal. Avoid any runs as they will creep around and out of site on you and dry that way and cause a streak in the finish that's near impossible to remove with additional coats. Thin, even, quick with as little overlap as possible. It should dry of the metals heat and then rust immediately (quick rust solution). Right then, put it back into the same tank of boiling water and grab the next part to do (if there is one). The brown rust on the part will change over the blue/black in a matter of moments but I leave it in the water for at least 10-15 minutes. Out again, shake it dry and now card it. Once carded it will probably be too cool to accept the next coating of solution (unless it's a rifle bbl or other heavy part and you work fast!) so back into the same tank of boiling water once again to heat up, then out,,shake it dry and apply coating #2. Once again even, quickly and thin. Don't scrub at an area as it will only thin out the previous coatings. You can use a piece of cloth pad, a small brush, or even clean 0000 steel wool to apply the solution. I use the steel wool usually for the first couple of coats then either a brush or small piece of cotton cloth pad. It doesn't have to be very big. Use a new pad for each new coat. If you see a streak or water spot appear and you're well into what otherwise is a nice job, I've found you can scrub that one area with fine scotchbrite to even it out, and the next coat or 2 will bring you back even. The base coats are still in the steel I guess so it doesn't take 5 or 6 to get it back matching again. You may have to change the water if it gets too dirty during the process. Alot depends on how clean the barrels are between the ribs and how much junk leaks out (can be a major headache at times!), how many parts/barrel sets you're doing and how many coats they need to complete. I usually do 5 or 6 on shotgun barrels and older rifle barrels(though they will look good after as few as 2 or 3). More modern stuff will take more and some will not blue well at all with this process. There's lot's of other little tricks like anything else you do but those are the basics that I can think of now and they have served me well in 40+yrs of rust blueing. Hope this helps.
