You can only have so much slip, then what? I found this technique a couple of years ago for reconstituting metal clay and I love it! I recommend it to all my students.
I used to HATE reconstituting old dried metal clay projects that didn’t work out. The main reason was because I didn’t have the right method. I always ended up with a big mess. With Lisa’s method I reconstitute all the time. Check this out and you will be able to use every bit of dried clay.
Here is a tip, I had some really old dried clay, like 5 years old. After I reconstituted it I found that the binder was old. The way to tell if the binder has broken down is to test it. Do a test with the clay by creating a very simple single layered charm. In the bone dry stage, sand as usual. If the piece starts to crumble or even fall apart then the binder has broken down. To solve this, add an equal amount of fresh clay to the reconstituted clay. Combine the two clays by rolling them out without any spacers (cards) Then fold the clays onto each other and re-roll. Do this this several times and your clay will be rejuvenated to a smooth workable clay!