Millstones have been used to mechanically grind indigestible seeds into nourishing flour since Roman times. The flour they make has become part of the daily diet of a third of the world‘s population, and without millstones, civilisation would be quite different.
Millstones are used in pairs. Those that run horizontally are called face grinders. The lower millstone, called the “bed stone”, is stationary; the upper stone, called the “runner stone”, turns about its axis. Millstones that are oriented vertically and ground on their edge are used to grind harder materials such as barite, cement, feldspar, gypsum, phosphate rock, mica and quartz. These millstones are called edge-runners or crushers.
In the colonial US, the early mills used millstones from Europe. Many of these millstones, called composite millstones, were shipped in pieces that could be carefully fitted together, cemented, and wrapped around the perimeter with iron banding.
Colonists preferred millstones from their homelands. Mills constructed by Dutch and German millwrights commonly used millstones made from bluish-gray lava flow rock first quarried near Köln (Cologne), Germany. These stones, called “Cullin” (Köln) stones, were first quarried by the Romans and were popular throughout Europe.
However, no millstone could match the famous French burrstone, a freshwater quartzite quarried in France. A special property of those stones was that, as they wore away, new sharp edges of quartz grain were exposed. Burrstones produced a whiter flour from wheat because it broke the bran (the dark, outer part of the grain) into large flakes. Other stones tended to finely shred the bran, which would pass through the flour-dressing machinery, resulting in a darker, coloured flour. French burrstones were found in most American mills in addition to other imported or native stones.
No machinery was available to quarry and shape a millstone – only hand-held tools and human muscles. Drill holes were beat into rock using hand-held bits hit with sledge hammers. Next, feathers (pairs of inverted L-shaped objects) were placed into the holes, wedges were put between the feathers and were tapped, one after another, until the stone split. Calipers from forked tree branches were used to scribe a circular outline of the stone, and specialised hammers, chisels and drill bits were used to shape to the line and create the hole for the axle. Other specialised hammers and picks cut furrows in the stone, which was called “dressing” the stone.
I can never cease to hanker for the rumble and grumble of the busy quarry, the sharp sound of steel on stone, and a slice of warm bread made from stone ground flour…
