(or other polymer clay, but I only tried this with sculpey brand)
I recently revived 9 different blocks of 10-year-old sculpey found in the back of my old desk. Here’s the method I developed, after working the first 4-5 blocks, that I believe will work with any color, type, or age of sculpey.
From what I’ve gathered in my (very) un-scientific research, Sculpey is made of PVC, colorings, and fillers and plasticizers to soften the material. When those softeners have lost their effectiveness through age, sculpey becomes brittle and unworkable. Most softening methods include re-adding some sort of softening agent so that you can yet again mold the clay. I settled with using Baby Oil, mainly because it was the cheapest recommended substance, and also because it was readily available in my house. Mineral oil is the same thing, and also acceptable.
To add the oil, the best method I found was to put the block of clay on a generous piece of parchment paper, and drizzle the oil (about a tablespoon, or however much it takes to cover the surface) on top of the clay. Then, let it sit for 12-24 hours. If you try to kneed the oil into the clay right away, you’ll end up with a partially sludgy substance with the potential to thickly cover your hands. (if you are impatient and this does happen to you, I recommend paper towels and lots of soap)
Work the Clay
After the oil has had a chance to soak into the clay, use a tool to chop your block of sculpey into many smaller pieces. It may still be crumbly and brittle inside – that’s okay. Then, take all of those small pieces and smush them together, in order to start re-forming them into one big ball of clay. I recommend keeping the pieces within the parchment paper at this point so that you don’t have to get the oil all over your hands.
The next part is going to take a little bit of time: you’re going to want to keep manipulating, stretching, and re-balling the clay until it begins to feel more elastic and new-clay-like. I’ve noticed some colors of clay take more time, with metallic clays (any color that looks shiny or glittery) often taking a long time or remaining slightly brittle. Temperature can also be a huge factor in this step. I had the best luck with all of my clays when I attempted to work them in around 85 degree heat. (It wasn’t the most comfortable sculpey-making situation, though)
Make Something Simple
Your newly rehydrated sculpey is never going to be 100% the clay it was before. So, I recommend using your zombie sculpey to make something that doesn’t require too much molding. I decided to create coasters by marbling the colors together and rolling it out into circles. Any other project that involves super simple shapes should also work out just fine.