This is a beautiful demonstration that can be used to illustrate issues of solubility, crystallisation and precipitation.
Lead iodide is made by precipitation and the resultant suspension is heated to about 60C. At this temperature the concentration of lead iodide that has been produced will dissolve.
The solution is allowed to cool and as it does so crystals of lead iodide will appear and settle to the bottom. When illuminated with a bright light, these crystals sparkle and glitter as they appear and fall.