Once the oil colour has been mixed it looks like a thick paste, but if you looked at it under an electron microscope you would see pieces of pigment of different sizes floating in the oil. To release the most brilliant colour, the pigment is ground to a very small and even particle size, using a triple-roll mill which replaced grinding by hand some 150 years ago. Not only does it save time and muscle power, it also gives consistent quality paint of the highest standard. The mill is made of three cylinders, positioned one behind the other, with a small gap between. The back and the front cylinders roll in an opposite direction to the middle roller, and at a different speed, crushing the pigment to supermicron fineness.
All colours go through the mill at least twice and some up to six times.
Quality Control A sample of milled colour is checked by Quality Control against standards going back five years and more to make sure that the tint, consistency, pigment size and density are to specification. Colour checking is done by eye. No colour can go any where in the factory until it has passed these tests. Once approved, it is packed into aluminium tubes, which are made to the same standard as those used in pharmaceutical industry. Each is coated inside to ensure that the aluminium cannot react with the colour.