Colour story: Cadmium Red

What is cadmium, and how was it discovered?

Cadmium is a moderately soft, silvery white metal with a melting point of just over 700 degrees Celsius. Cadmium compounds were discovered by chemist Friedrich Stromeyer in 1817 – relatively recently when compared to popular pigments – and they have been used to produce colour ever since.

Cadmium paints became more available to artists after commercial production began in Germany in the 1830s. Winsor & Newton showed cadmium yellow at the 1851 Crystal Palace exhibition. During this period they were highly valued for their permanence, brilliance, opacity and mixing capabilities, though they were expensive.

From yellow to red

Stromeyer recommended using bright yellow cadmium sulphide in artists’ colours, and it was some time after the introduction of Cadmium Yellow that Cadmium Red began to appear. The early reds were made by heating the yellow together with selenium, and in 1919 a patent was registered for the production of Cadmium Orange and Cadmium Red.

The method involved mixing cadmium salt solutions with alkali and alkaline earth sulphides, which in turn heated the solid collection of particles left in the solution.

A carefully controlled process

The production of modern, high-performing Cadmium Red is an expensive and lengthy process. It must use only the purest raw materials to produce the best possible colour, and transforming cadmium metal into a usable pigment involves several carefully controlled chemical reactions and procedures. These use ingredients such as mineral acids, sodium sulphide flakes, water and selenium.

When heating takes place towards the end of the process, the quality and hue of the final pigment starts to form. This pigment is then ground down into tiny particles. The grinding process affects the way the pigment interacts with light. For example, fine particles have a good diffused reflection and therefore produce a very strong, vibrant colour.

Is cadmium toxic?

Cadmium is a heavy, toxic metal, but cadmium pigments are not classified as dangerous for use in line with EC classification. In fact, in the early 20^th century it became a natural replacement for the distinctive but toxic Vermilion. The level of soluble cadmium in the pigments is so low that they pose no greater risk after swallowing or breathing in than other pigment types. And so, while cadmium pigments are restricted for some applications, this does not apply to artists’ colours.

A pop of colour

Cadmium Red will add brightness, strength, warmth, opacity and a touch of passion to any artist’s work. It has been a staple for artists since the 19^th century, from Claude Monet to Edvard Munch. Today it remains a reliable alternative to Vermilion, either natural or synthetic, and an essential colour for creating bold, eye-catching works.