Īshlar may be coursed, which involves lengthy horizontal layers of stone blocks laid in parallel, and therefore with continuous horizontal joints. Ashlar is related but distinct from other stone masonry that is finely dressed but not quadrilateral, such as curvilinear and polygonal masonry. Īshlar is in contrast to rubble masonry, which employs irregularly shaped stones, sometimes minimally worked or selected for similar size, or both. Generally used only on softer stone ashlar, this decoration is known as "mason's drag". One such decorative treatment consists of small grooves achieved by the application of a metal comb. Precisely cut "on all faces adjacent to those of other stones", 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. Ashlar is the finest stone masonry unit, generally rectangular cuboid, mentioned by Vitruvius as opus isodomum, or less frequently trapezoidal. The blocks were laid randomly without continuous courses or vertical and horizontal joints.Īshlar ( / ˈ æ ʃ l ər/) is finely dressed (cut, worked) stone, either an individual stone that has been worked until squared, or a structure built from such stones. Although each block was cut with great precision on adjacent faces, the external face was left rough as when removed from the quarry. Quarry-faced red Longmeadow sandstone in random ashlar was specified by architect Henry Hobson Richardson for the North Congregational Church (Springfield, Massachusetts, 1871).
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