Why has hand grinding pigments become less common in the manufacturing of colours?

Up until the late 18th century, hand grinding was the principal method of making artists’ colours. Skilled workers would use a shear/slide method with a stone muller and flat slab to disperse the pigments into the binder.  Hand grinding required knowledge and expertise to bring out the individual characteristics of pigments. Without this skill, the subtle variations required in grinding different pigments were lost. Hand grinding was, however, a very labour intensive and difficult method of creating artists’ colours; for scaled up manufacture of colour in the 21st century, it is very impractical.

At Winsor & Newton, the Triple Roll Mill is used to manufacture our artists’ colours. This process has been used for grinding colour for many years because its action improves that of hand grinding. Today, even the triple roll mill is viewed as old technology but it is still the best method of producing the quality required. This method of dispersing the pigment particles into the binder ensures that the pigment mass is broken down and ground into the binder in a much more consistent way than could ever be achieved by hand. Mills themselves vary; depending on the pigment being ground, they range from mild steel to ceramic to granite rollers, for softer pigments.