Altarpiece unclear. Altarpieces can still broadly be divided into two types, the "reredos", which signifies a large and often complex wooden or stone altarpiece, and the "retable", an altarpiece with panels either painted or with reliefs. Retables are placed directly on the altar or on a surface behind it; a reredos typically rises from the floor. Retable-type altarpieces are often made up of two or more separate panels created using a technique known as panel painting. The panels can also display reliefs or sculpture in the round, either polychrome or un-painted. It is then called a diptych, triptych or polyptych for
Early Netherlandish painting time. That hinged works could be opened and closed served a practical purpose; on religious holidays the more prosaic and everyday outer panels were replaced by the lush interior panels. The "Ghent Altarpiece", completed in 1432, had different configurations for weekdays, Sundays and church holidays. The first generation of Netherlandish masters borrowed many customs from 13th- and 14th-century Italian altarpieces. The conventions for Italian triptychs before 1400 were quite rigid. In central panels the mid-ground was populated by members of the Holy Family; early works, especially from the Sienese or Florentine traditions, were overwhelmingly characterised by images of the enthroned