Pigmented structural glass

Pigmented structural glass is a manufactured, opaque or nearly opaque coloured glass produced in thick sheets or slabs, primarily for architectural use. It was widely used during the early to mid-20th century as a durable decorative facing material for shopfronts, building façades, interior walls, partitions and sanitary surfaces. Well-known trade names include Vitrolite, Carrara Glass and Sani Onyx.

The material is generally a soda-lime silicate glass containing pigments or opacifying agents dispersed throughout the glass body. It was manufactured in numerous colours, including white, cream, black, green, blue, red and yellow. Some varieties were intended to imitate polished marble, onyx, jade, jet or other ornamental stones. The exposed face was normally smooth and highly polished, while the reverse may be roughened, ribbed or grooved to improve adhesion to a wall or other supporting surface.

Broken fragments are commonly encountered in demolition waste, old industrial areas, rivers and on beaches. After prolonged abrasion by sand and water, their surfaces may become rounded and frosted, making them resemble pebbles of jade, jasper, chert, marble or other fine-grained rocks. Beach-worn pieces are sometimes collected as a form of sea glass.

Pigmented structural glass may usually be recognised by its uniform artificial colour, vitreous fracture, absence of mineral grains or natural texture, and occasional remnants of flat polished surfaces or parallel grooves on the reverse. Thin edges of apparently black or very dark material may transmit coloured light when examined against a strong light source. Unlike natural stone, it commonly shows conchoidal fracture and may contain small rounded bubbles, flow structures or other evidence of glass manufacture.

Despite its historical name, pigmented structural glass was normally used as a surface cladding rather than as a load-bearing structural element. It is an anthropogenic glass and not a mineral or natural rock.