These bricks, now obsolete, were classified into three groups: enamelled; sprayed, and salt glazed. The enamelled and sprayed bricks were made from a low grade fireclay in a manner similar to producing a good quality pressed brick but the spray glazes were sometimes applied to the green brick; these were used, internally and externally, where cleanliness or light reflection was required. Brown salt-glazed bricks were made in an entirely different way. When the kiln was at maximum temperature softwood chippings and common salt were inserted to create a salt vapour that was absorbed by the body of the brick. Extensively used for sanitary and acid resisting brickwork.