White - Science - Chemistry- White Pigments and Dyes

Chemistry- White Pigments and Dyes

Chalk is a kind of limestone, made of the mineral calcite, or calcium carbonate. It was originally deposited under the sea as the scales or plates of tiny micro-organisms called Coccolithophore. It was the first white pigment used by prehistoric artists in cave paintings. The chalk used on blackboards today is usually made of gypsum, a powder pressed into sticks.

Bianco di San Giovanni is a pigment used in the Renaissance, which was described by the painter Cennino Cennini in the 15th century. It is similar to chalk, made of calcium carbonate with calcium hydroxide. It was made of dried lime which was made into a powder, then soaked in water for eight days, with the water changed each day. It was then made into cakes and dried in the sun.

Lead white was being produced during the 4th century BC; the process is described is Pliny the Elder, Vitruvius and the ancient Greek author Theophrastus. Pieces of lead were put into clay pots which had a separate compartment filled with vinegar. The pots in turn were piled on shelves close to cow dung. The combined fumes of the vinegar and the cow dung caused the lead to corrode into lead carbonate. It was a slow process which could take a month or more. It made an excellent white and was used by artists for centuries, but it was also toxic. It was replaced in the 19th century by zinc white and titanium white.

Titanium white is the most popular white for artists today; it is the brightest available white pigment, and has twice the coverage of lead white. It first became commercially available in 1921. It is made out of titanium dioxide, from the minerals brookite, anatase, rutile, or Ilmenite, currently the major source. Because of its brilliant whiteness, it is used as a colorant for most toothpaste and sunscreen.

Zinc white is made from zinc oxide. It is similar to but not as opaque as titanium white. It is added to some breakfast cereals, since zinc is an important nutrient.

Chinese white is a variety of zinc white made for artists.

• Titanium white, made with titanium dioxide, is the brightest white paint available. It also colors most toothpaste and sunscreen.

• Zinc white, made from zinc oxide.