A while back my kids and I made some glow in the dark slime. As cool as this activity was, it was even more interesting to watch the slime age. As each day went by, more and more of the water evaporated, shrinking the slime ball. Eventually it was as thin as an extremely thin pancake. Imagine someone making very runny pancake patter and trying to make a pancake with it. You'd end up with a pancake no thicker than a piece of paper. That is what our slime looked like! In addition, mold was growing on it. LOL! I wish I had a picture, but my wife tossed the slime before I could take one. Boo to her! :-)
Imagine the above pancakes looking less edible with growing mold on the surface and you have our aging glow in the dark slime!
If you make slime with your kids, makes sure to document the slime for several days after it is made. Note how it changes and why. It's a 2-3 week long science experiment!