This process can take as long as four hours, but it is not the finished paint. Under close inspection, vast quantities of the pigments still cling together rather than being individually coated. This is where the triple-roll mill comes in.
A triple-roll mill is at the heart of paint-making. At its most basic, it is three horizontal granite rollers that each run at different speeds and spin in alternating directions. The paste is scraped out of the mixer’s bowl with a baker’s blade and dropped into the hopper. Each giant dollop makes a delicious slap as it plops onto the rollers below. The paste is drawn down into the tiny space between the rollers, again and again. With each pass, the space is narrowed to more aggressively separate the pigment particles.
If you have ever used a pasta-making machine with its two rollers forcing the dough through the small space between them, you can understand the paint-making process. Just as the roughly made dough cannot pass through the narrowest setting first, so the pigment-paste must be passed through the mill rollers multiple times. It’s just that our mill is like a pasta-machine on steroids, with three rollers rather than two and a massive motor to drive the material through. For soft pigments, such as zinc white, only three passes are needed, but the synthetics can take up to nine passes. Synthetic pigments are very difficult to prize apart: Their incredibly small size and specific shape mean they have to be painstakingly teased into dispersion.
The paint-maker must be constantly attentive to the vagaries of milling. Rollers heat up under the friction of pigment particles, which alters the size of the roller gap, and the fluidity of the oil is affected by changes in ambient temperature. Also, pigments behave differently from one batch to another. This is especially true of the natural earths, which vary in their mineral make-up depending on the part of the seam the earth was dug from.
Towards the end of the paint-making process, we take samples of the paint and test it for quality. Historically, paint-makers would rub the paint between their thumbnails—a simple but surprisingly delicate solution to feel for the grittiness of unmixed pigment. Nowadays, we use a precisely honed stainless-steel gauge to check the quality of dispersion.
But we are still not ready to sign off on the product. Two extremely thin films of the freshly made paint are applied to paint-maker’s cards. One daub is the pure paint. The other is the paint mixed with a specified amount of titanium white. By placing the card next to one from a previous batch of the same color, we can ensure that every time we make the paint it has identical color, tinting strength, tint color, and undertone to all previous versions.
Only after the paint has passed these tests is it approved for packing. It is hand-filled into collapsible aluminum paint tubes, labelled with hand-painted swatches of the individual color, boxed and shipped to studios around the world.