The Celtic fret is chiefly a diagonal one, but the recurrent angle is rounded to a curve.
Chinese and Japanese frets are usually right-angled, and are used in great profusion, often in a secondary field or background.
The Japanese key or “Fret diaper” is used in the greatest profusion; it is used alike on silks and brocades, damascened in metal, in cloisonné enamel and in lacquered work, and is frequently arranged in irregular shaped compartments or medallions.
The Greek continuous fret border is rarely used by the Japanese, who generally use the disconnected or irregular fret. A similar irregular fret border was used by the Peruvians ([plate 41]), by the Mexicans, and by the natives of Polynesia.
The Assyrian and Byzantine guilloche is but a curved fret, but additional interest is given by the introduction of radiating forms in the principal interstices of the fret (fig. 5, plate 11.)
