How can I revive hardened plumber's putty?

Linseed oil. Very little plumbers' putty is used anymore. Caulk, both latex and silicone are what they seem to be going thing.

It's a gonner. Use as a door stop and buy new. Going forward, put it in the house. After you've finished your project(s), press plastic wrap onto the top and up the sides, sealing well. Make sure top is on tightly. Will last a lot longer.

The best way to re-soften plumber's putty is to pour oil directly on top of it, replace the lid and wait. After a few days, open the container and stir. Check the container for the list of ingredients and match the oil used by the manufacturer. Avoid putting the putty in the microwave

Once hardened it will never be make soft again. Maybe smaller quantity next time if poss.....

Lowe’s sells a tube, easily closed, for less than $5.

There are plastic tubs for about $3.

WD40 is the instant cure. Work it in a little and there's your putty.

I would buy new, you wouldn't want to mix anything with it that will compromise its effectiveness.

Linseed oil.

Has anyone used mineral oil. It is used on cutting boards to protect it and goes into lip balms.

I've faced a similar dilemma with my plumber's putty. What I've learned is that the longevity and effectiveness of the putty can depend on how it's stored. Ideally, it should be in a cool, dry place. If you're unsure about using the old putty, maybe it's time for a professional opinion before diving into any DIY repairs. I recently reached out to a plumber near denver who gave me fantastic advice on plumbing essentials and their shelf life. They're quite knowledgeable, and I'm sure they'd offer some insights if you're in the area.

I'd start over with a tube of plumber's putty.

Hi! You can try putting water and lotion into it. Hope this helps!