Copper(II) hydroxide: The slightly darker blue stuff
Copper(II) hydroxide has been known since copper smelting began around 5000 BC although the alchemists were probably the first to manufacture it. This was easily done by mixing solutions of lye (sodium or potassium hydroxide) and blue vitriol (copper(II) sulfate), both chemicals which were known in antiquity.
It was produced on an industrial scale during the 17th and 18th centuries for use in pigments such as blue verditer and Bremen green. These pigments were used in ceramics and painting. It also occurs naturally as a component of several copper minerals, notably azurite and malachite. -x