impost

Horizontal projection immediately below the springing of an arch, sometimes immediately above the capital, sometimes used instead of a capital. Not to be confused with an abacus. The commonest 12thc. forms are chamfered, and hollow-chamfered. Either the upright face or the chamfer may be decorated, and there may be a quirk or an angle roll between face and chamfer.

inclined jambs

Jambs arranged so they lean inwards towards the centre of the opening; a system more common in Ireland than elsewhere in the British Isles.

interlace ornament

A form of decoration where individual carved strands or straps are intertwined, usually forming geometrical designs.

intrados

The inner surface of an arch. See also soffit, extrados.

inverted cushion base

A base like an inverted cushion capital. Scalloped forms are also known.