The jacket it blued in large tanks that Chris DwWitt at the NSRM CC designed. The solution is heated. The jacket is not blued all at once, but is rather done in its separate segments with all the holes for rivets and check valves already cut in. After the bluing process is completed it is riveted together with brass rivets. The jacket has been on Eureka for about 25 years and has held up remarkably well. If you want to know the exact process I would suggest contacting Chris at the NSRM CC. I do not have the chemical composition, but the results are beautiful in my opinion. When we first blued Eureka's jacket we also did the Inyo's jacket at the same time. Chris is getting ready to do the Glenbrook's jacket using the same process.
It is best to cut the sheets and fit them up around the domes before the process begins so that all surfaces are treated. If you try to do the fit up after bluing, you may damage the finish and have areas that are not protected. During the fit up I used cleco fasteners, which are used on aircraft aluminum to connect all segments hold the shape during the fit up.
Once the jacket is all in place on the boiler it is best to keep the jacket oiled periodically to help protect it further. I have found that WD 40 or LPS 2 works for me.