Pressing tiles

In 1840 Richard Prosser discovered that dust clay could be compacted with a press, making tiles from a drier body instead of damp plastic clay. The tiles dried faster and warped less in firing, and the great Victorian tile boom began around 1850, according to a British tile society's guide. Digitalfire describes the modern descendant: clay powder pressed at high pressure, for example 500 kg/cm², into metal moulds, which needs minimal drying facilities. Tile makers have learned to press and fire tiles of more than a square metre.

Pressing also exists on a craft scale. In Barcelos, plastic paste is put into a positive mould and pressed by a negative one, a technique used for roasting dishes, frying pans, plates and caldo verde bowls. For tiles, a potter writing in Pottery Making Illustrated calls a one-piece plaster press mould the most effective way to make handmade tiles, less prone to warping than rolled slabs, advises calculating the clay's shrinkage beforehand and warns that a tile bent when released from the mould will most likely warp in the final firing.