Copper sulphate is formed by the reaction of copper and sulphuric acid. The resulting solution is blue in colour and when supersaturated, forms blue salt crystals. The blue colour is used in dyes and stains quite easily. Copper sulphate is also highly toxic, so care should be taken to avoid contact with skin and eyes. It should also be used in a well-ventilated area. The pretty blue crystals formed from the solution make copper sulphate experiments popular in classrooms.
Warm your water in a glass beaker but do not boil. The higher temperature causes the copper sulphate to be more easily soluble.
Stir about 25 mg of copper sulphate into the water. Add more copper sulphate a little at a time until it no longer dissolves.
Cool the beaker to room temperature, or in a refrigerator for quicker results. As the water cools, crystals will form and drop to the bottom of the beaker. Once this happens, the solution is no longer supersaturated.
Pour the solution through a strainer into another glass beaker to remove the crystals. The crystals can be used as seeds for new crystals and the saturated solution in the beaker can be reused to make a new supersaturated solution.
Handle chemicals carefully. Always use skin and eye protection. Do not swallow.