Saw bottles of blueing liquid on the shelf at my local shop. Are these products worth anything?

Mostly, they're for touching up small scratches and worn spots.
They often don't work well on larger areas.

Some problems:
They tend to leave a blotch in the original blue around areas where cold blue has been used. This is permanent.

The color never matches the original bluing.

On larger areas it tends to produce a smoky blue-gray splotchy look.

Cold blues are not durable at all. You can literally wipe it off with very little rubbing with a thumb.

Cold blues tend to turn brown.

Cold blues may actually cause rust due to chemical action.

Bottom line, while some people get fair results with a cold blue, it is at it's best as a touch-up for small areas.

Most bottled cold bluing is a rather weak acid and basically just discolors the surface. The problem is it will keep on oxidizing till it fades to an ugly greyish color. It is quite different from the chemicals used to do true "slow-rust bluing" or hot-tank bluing.

Everything dfariswheel said! It isn't good for much of anything IMHO except a very temporary fix.

I figured it was not a "good" fix. I would never consider having anything done to one of my guns unless it was sent back to S&W and done by the pros!

I wonder how many people have ruined guns with this stuff. I guess Barnum was right.....A sucker born every minute.

Cold blue can be successfully used on your old shooters. Guns that aren't ever going to be collectible. I've used Birchwood Casey Permablue several times on old mod 10's with a bunch of barrel tip and cylinder wear, (former LEO guns), and it will help protect the worn area's. If you heat the area with a hair dryer first, then follow the instructions on the bottle you may be surprised how good they come out. Multiple applications, polishing in between with 0000 steel wool, and then coating with gun oil and letting sit for a few days does help.

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H Richard
SWCA1967 SWHF244