With the effort of polishing, prepping, and etc it wouldn't make much since to cold blue as the hardest part of any blue job regardless of cold blue, rust, hot salt, and nitre blue is the preparation of the material. To put that level of prep into the barrels without finishing it right would be a shame. I only had intentions of bluing one set several years ago and have since done dozens. The input costs of rust bluing is minimal if you are doing the work as the materials are nothing more than steal wool, acetone, rain water/distilled, and a rusting solution. Tanks are relatively inexpensive and can be reused indefinitely if maintained. A camp stove at minimal and a showroom level job can be achieved. I talked with charles danner of fayetteville tn who did a 16 gauge set for me in the beginning of my collecting. He went through all the basics with me and since then I've learned alot through trial and error. Although rust bluing is a skill, all that is being done is using acids and salts to oxidize steel. Anyone could do it as preparation is everything.