Wood’s Glass

Gina uses a Wood’s Glass in Mrs H’s Knitting Circle.

Robert Wood developed the Wood’s Glass during World War I. The Wood’s Glass filters light removing the visible components of a beam of light leaving the ultraviolet and infrared components. This “invisible radiation” was used during World War I as an invisible signal beam.

Wood’s Glass is a barium-sodium-silicate glass with 9% nickel oxide. The glass is a deep violet-blue to the eye. It is more vulnerable to thermal and mechanical damage than normal glass. It is also prone to slowly developing a layer of hydroxides and carbonates when exposed to atmospheric moisture and carbon dioxide. Wood’s glass undergoes solarisation becoming less transparent to ultraviolet light over time. As a Wood’s Glass bulb produce little visible light a user may accidentally overexpose themselves to ultraviolet light.

Modern Wood’s Glass bulbs are often made from other types of glass with an ultraviolet filtering enamel surface coating because of these problems. These bulbs pass far more visible light than a genuine Wood’s Glass bulb.

Wood’s Glass is often used to create filters instead of being used for the material of a light bulb. These are placed in front of a bulb to remove the visible light. Wood’s Lamps are made with Wood’s Glass and are used in medicine for diagnosis. Wood’s Glass is used in photographic filters and some black lights.

Featured In: Mrs H’s Knitting Circle