How do you obtain big crystals of blue vitriol from its solutions?

Answer 1

Crystals in general are formed when solutions try to maintain concentrations at or below saturation. For example, a saturated sugar solution forms crystals when water from the solution evaporates and leaves excess sugar behind. Since supersaturation is a highly unstable and thus undesirable state of being for a solution, the dissolved sugar left behind will clump together at sites of nucleation to let the remaining solution remain below supersaturation. Crystals will continue to grow as long as the concentration of solutes in the solution can increase above saturation.

To grow large blue vitriol crystals, one can simply prepare a saturated solution in a large container and let it sit undisturbed for as long as possible while evaporating steadily, removing the crystals when they are a satisfactory size or before the solution dries up entirely.