Ashlar is finely dressed (cut, worked) masonry, either an individual stone that has been worked until squared or the masonry built of such stone. It is the finest stone masonry unit, generally cuboid in shape.
Precisely cut, ashlar is capable of very thin joints between blocks, and the visible face of the stone may be quarry-faced or feature a variety of treatments: tooled, smoothly polished or rendered with another material for decorative effect.
One such decorative treatment consists of small grooves achieved by the application of a metal comb. Generally used only on softer stone ashlar, this decoration is known as mason’s drag.