I put some cardboard in the barrel and then on top of that a piece of polymer clay, to seal any gaps. I then mixed up some green clay with liquid clay to get a slimy colour. I put some of the glass balls in the barrel and poured the liquid clay over the top, just so it started to run down the side. Popped it in the oven and this is the result. The liquid clay did continue to run, but it's formed a lovely puddle around the Barrel..
I'll be back later, with the other experiment I've tried..That one involves glass paint..