It depends. Do you have lots of small pieces, or larger chunks? If you have a lot of small stuff like trimmings, mix it with water and then you can put it on a piece of plaster or a clean spot on the concrete or on a piece of heavy canvas to suck the water out. You can also put it in the sun to speed things up. It will dry unevenly and you'll have to wedge it a lot.
If you've got big pieces, you can wrap them in a wet towel and put them in a 5-gallon bucket with a lid and let them sit, re-wetting the towel every day, until they get workable again. It may take a while, so when you can cut pieces off, you can dip them and wrap them in plastic---and keep doing that until the whole piece becomes workable. Again, you'll need to wedge a lot to even it out.
I use reworked clay all the time. I also mix it with new stuff, and I think the extra bacteria helps make the whole batch better.
I have some pieces I cut out and decorated to put together some small square planters, but I inadvertently let them dry out before I got to putting them together. Since they're basically ready to just put together is there any way to wet them slowly and have them workable as is again?
Someone told me to set them on a pretty damp towel that is on plastic and cover with a similar towel and more plastic, and that they'd slowly be workable again. They also said to occasionally spray them lightly as they were rehydrating so it would happen slowly. I know that if I get them too wet all at once they'll just melt. Any comments on this or other ways would be appreciated.
Have you got a cooler you're not using? Either dip them in water very quickly or spray them with water and put damp (not wet) paper towels over them and leave them overnight in the cooler. If they're not ready by morning, you can spray them again. When they get back to being about leather-hard (or a little drier) you can score them and brush water just on the places where you want to join them. After you get them assembled, spray them all over again and put them back in the cooler to "even out" for a couple of days before you take them out to dry.
imapigeon thanks so much for your detailed description of how to rewet a project & or it's pieces! My instructor has basically said that once they're this dry it's too late and I know if I wet them too fast they just turn back into clay mush, so this is great.
I go to a ceramics class twice a week and often bring home partially completed projects that I think I'll have time to complete and then run out of time or forget about them. So, unfortunately I have multiple projects spread around the house that are now a bit too dry to work with and I hate to keep turning the dried pieces into my future slip bowl, which was about to become a bucket before your handy tip.
Think I'll take pictures of the process of rewetting the box planter project as I go so I can share them here and in class.
Please do---I hope it works! I just attached decoration to a bowl that was really too dried out, and now a couple of days later I've had to brush some paper-clay slip on it to keep the decorations from cracking. You can also brush a little vinegar on the cracks, which will react with the clay a bit. We used vinegar slip all the time to help students make repairs on their over-dried slip-cast pieces when I taught classes.
Oh, and P.S.----unless you've put a ton of time into a piece and want to salvage it, it's often EASIER to just start over. That may be your teacher's approach!