Weekend chemistry: growing copper acetate monohydrate crystals larger by evaporation. These crystals and clusters of crystals, ranging 1mm-2cm in size, are in a bowl with roughly 300 mL saturated copper acetate solution. As the solution evaporates, more solid copper acetate will deposit on the surface of the crystals. The solution appears deep cobalt blue in the pictures, but is more of a deep aqua color in person. The crystals are so intensely colored they appear black, except on the thinnest edges.

My boy making lovely blue crystals.