This is typical of an old faucet. The calcification is just a minor buildup, it can be removed. I would repair it this way:

1. Shut off the water supply to the bathroom (this may be the main house shut off).

2. Disconnect the line going to the toilet from this valve.

3. Remove the valve handle and the large packing nut below the handle. The aim is to open the internal valve passage to the supply pipe to drain the water, push the pipe down if necessary to get it to drain completely.

4. With a propane torch and channel-lock pliers, heat the solder joint at the base of the valve and remove the valve from the supply pipe. They don't always slide off easily, usually one has to put twisting and/or bending forces on the valve to get it off. This is all normal.

5. Remove the trim escutcheon.

6. With a torch and an old cotton t-shirt, heat the globby solder on the supply pipe until it melts and wipe the pipe clean with the cotton rag. Do this several times if needed, and keep several layers of cotton between your hand and the hot pipe! The pipe should be clean and smooth now.

At this point you can reinstall an escutcheon and valve. I like the new 1/4-turn shutoff valves, but I'm hesitant to put soldering heat to them like you see the plumbers doing, so I buy the 1-/4 turn valve with a compression fitting and just tighten it onto the 1/2" copper line with pliers. Did that to all my sink and toilet shutoffs when we built the house with no problems.

Ok, Stax, I agree. Any new installation should include abrasive cleaning of the pipe surface. I prefer a roll of cloth backed sandpaper. Wire brushes work, too.

Thanks yall. Glad to hear it's not FUBAR

Is there a way to get it off without torch? I don't have those skills.

Was looking at Shark Bite most likely for replacement valve or maybe compression like you suggested. But removing it sounds like I need to get a torch.

You can cut the 1/2" copper supply pipe with a tubing cutter, BUT you shorten the length of pipe extending out from the wall. That can be a problem for obvious reasons.

To get the old fitting off, one doesn't need skill with a torch. Get it hot enough to melt the solder, keep heat on it, and pull/twist on the valve with pliers. Kind of a brute force approach. It's not glamorous in any way.

Sounds good. That gives me a lot more confidence. Looks like someone gets to play with fire!

I've got two other (sink) valves that don't shut all the way, gonna see if I can just replace the washer on those.

Might take a couple weeks, but I'll post when I'm done. Appreciate the help!

Soldering copper pipe is a good homeowner skill to learn. And, it's easy to do. When you buy the torch, pick up a short length of pipe, some fittings to practice with, and a soldering kit like this:

https://www.menards.com/main/tools/torches-soldering-tools/oatey-reg-safe-flo-silver-plumbing-solder-kit/50683/p-1444449926798-c-8533.htm?tid=-8460164875200987733&ipos=2

Clean the inside and outside of all the pipe surfaces where they would overlap with the sanding cloth, surfaces should be bright and shiny copper. Apply a small amount of tinning flux to all surfaces, assemble things and its ready to solder. Turn on the torch and set it on a level surface in front of you. With channel lock pliers, hold the assembly with one hand and bring the assembly into the heat of the flame. Not into the base of the flame, stay more towards the flame tip. If you overheat the joint, the surfaces oxidize and you're done, the joint will never solder properly. Bring the joint temp up slowly, the tinning flux will start to bubble, and with the roll of solder unwound/extended and in your other hand, test the joint with the solder on the opposite side of the heat. As the joint comes up to soldering temp, the solder will melt and be drawn into the joint by capillary action. The joint is done! You can wipe the joint with a cotton rag to clean it up if desired. As the joint cools the solder solidifies. You can touch/drape a wet cotton cloth around a joint to speed up its cooling, or if I'm preassembling several fittings at a bench, I like to drop the assembly into a bucket of water so I can handle things quicker.

Soldering to pipes with water in them can be tricky.

Carefully cut the pipe with a hacksaw right behind the fitting; you won't get as close to the fitting if you use a pipe cutter. Clean the pipe and use a compression valve or a Shark Bite please.

Remember, this is a project that you have to finish once you start as you're only getting one toilet flush when it's underway.

Michael-

In case you decide to use a torch, be aware that, after you have shut off the water to the stop, you need to have the valve open before you apply a torch. If you don't do that, you will generate steam which can cause a pipe explosion.

Best to open a tap somewhere on a lower level to drop the water in the line so you have a dry line to work with. If you’re worried about torching anything close to the valve, there are heat resistant cloths and mats available to put underneath or behind your work. Good luck. We just replaced our old valves and a couple of them ended up needing to be cut and extended. Can be a PITA.