Regular testing of new batches of watercolour pigment in the laboratory of Winsor & Newton is necessary to verify the quality and repeatability of the pigments that we use. To do this, we make a test sample from every new batch of watercolour that we buy. We take a small sample from the new batch of pigment and use our muller machine to combine it with a solution of Gum Arabic to create a watercolour sample. The muller is then set to run for 25 revolutions, the paste is then collected to the centre of the plate and set to run for 25 revolutions more. The rudimentary watercolour created is then used to create a graded wash which is compared to a master sample that we keep. When evaluating the watercolour from the new batch, we are comparing the masstones and undertones through the wash in the new sample with our master to ensure the quality is up to our standards.