how do you blue a gun? I have several old guns I would like to fix up.?

Take it to a gunsmith who specializes in bluing firearms.

It is extremely difficult and time consuming to reblue a gun at home and it is difficult to get an even depth with cold blue. if you want a professional result, it needs to be hot blued. The equipment for hot bluing costs a couple of thousand bucks or more.

Save yourself a ton of headaches and let a pro do the job.

Doc

Combine Doc Hudson & Fate's answers-ALWAYS get an appraisal from someone before you ever do work to an older gun-there are a few out there that look like crap,but if you try and "fix them" you just dropped the values from several thousand to hundreds of dollars. I'm not saying you have a collectible-but let's pretend you do till you get them evaluated. Now if these are old sporterized rifles that someone chopped on and drilled and tapped it,etc, then it isn't a big deal,but there are even 22 rifles that bring in significant $$$.

After you have the appraisal or evaluation, then the Hot Blue method is definitely the best way to go.There is no way a home kit cold blue product is going to give you anything close to what you really want a gun to look like. There are times when this is best left to professionals-especially if you want to restore the best look possible. Again, if you have a hint of a collectible gun DO NOT REFINISH IT in any way, at least until you determine the economic impact.

Of course not every rifle is worth re-investment at the scale of professional re-bluing,then the Brownell and Birchwood - Casey stuff is worth looking at.

Bluing is a type of controlled rusting. It uses caustic and poisonous chemicals to accomplish the proper result. None of which is something you can do at home. However, there are some "cold blue" products available from places like Brownell's, but the result is far from that of the real process. Some old guns were not blued, but rather "browned" and this is a simple process that CAN be done at home. Products are available from brownells and places like dixie gun works. The number one problem is you must be able to remove old finish to bare metal, and then be able to bead blast etc the firearm to remove every single defect or it will show very badly. Having it redone by a pro is not really that expensive, and guarantees an excellent result.

shoot safe

What kind of guns? Anyone with sense will say to leave them as they are. Cleaning an old gun really good or refinishing it will take over half the value away if they are worth anything.

Fatefinger hit the nail on the head. Don't reblue them.