guilloché

thumb|An engine-turned (guilloché) watch dial made by Derek Pratt (watchmaker)|Derek Pratt and rejected by him due to imperfections that are almost invisible to the bare eye. thumb|250px|Ancient Roman art|Roman guilloche around a scene with Diana the Huntress, late 2nd century AD, mosaic, Bardo National Museum, [[Tunis, Tunisia]] Guilloché (), or guilloche (), is a decorative technique in which a very precise, intricate, and repetitive pattern is mechanically engraved into an underlying material via engine turning, which uses a machine of the same name. Engine turning machines may include the rose engine lathe and also the straight-line engine. This mechanical technique improved on more time-consuming designs achieved by hand and allowed for greater delicacy, precision, and closeness of line, as well as greater speed.

The term guilloche became also used more generally for repetitive architectural patterns of intersecting or overlapping spirals or other shapes, as used in the Ancient Near East, classical Greece and Rome and neo-classical architecture, and Early Medieval interlace decoration in Anglo-Saxon art and elsewhere. Medieval Cosmatesque stone inlay designs with two ribbons winding around a series of regular central points are very often called guilloche. These central points are often blank, but may contain a figure, such as a rose. These senses are a back-formation from the engraving guilloché, so called because the architectural motifs resemble the designs produced by later guilloché techniques.