Millais was able to buy tubes of paint mixed by colourmen that he could use straight away. New pigments were developed throughout the nineteenth century. Millais had a wide choice of pigments that came from minerals, precious stones, rocks, vegetables, insects and plants. Some of the new colours he used came about by the advances of modern chemistry. He used: lead white, zinc white, ultramarine ash, vermilion, chromium oxide, zinc yellow, chrome yellow, cobalt blue, Prussian blue, burnt sienna, Naples yellow, madder lake, ivory black and bone black. Millais’s greens were mixed greens of chrome yellow and Prussian Blue, possibly from a tube of green paint.
Millais would have mixed his oil paint (a mixture of pigment and oil) with another liquid to make the pigment more fluid and transparent. This liquid is called the medium and Millais used copal medium, a resin (a sticky substance produced by trees) dissolved in oil to make the paint more fluid.
Before the introduction of ready-made paint, artists had to mix paint themselves. This involved grinding the pigment (the small coloured particles of colour) and mixing it with a medium. The dry pigment was ground on a slab using a muller (shown above) and water. The water was then evaporated and the pigment mixed with an oil medium using a spatula or palette knife so that the paint could be easily applied and used. Mixing machines with electronic motors took over this procedure for most colours in modern times, which made the production of paint quicker, cheaper and safer.