I have just remembered. Many years ago I was playing with simple yet fascinating experiment. You take a solution of sodium silicate and drop crystals of different salts into it - copper sulfate for example. Some red crystals gave the best effect but some of you where not even planned at the time when I did the experiment so please don't ask me what it was as I don't remember
What happens is that silicates precipitate on the crystal surface and they form a thin, semi permeable membrane. Water goes in, membrane breaks, solutions flows out, new membrane is created. Different salts give different shapes and different colors.
I have no reagents at hand now so I can't repeat the experiment, but I suppose some of you may have everything needed at hand (Wilco?)Edit:
these red crystals... I had potassium ferrocyanates (both) from some "Young chemist" set. So these are suspected.