“Sun-purple” glass is created when certain types of glassware are exposed to strong UV light. Much “sun-purple” glass is created intentionally by unscrupulous or ignorant dealers who want to convince their buyers that the glassware is antique. This damage is irreversible, and is ruining many of our historical artifacts. Attempts to “repair” sun-purple glass by heating it will result in glass that is still discolored, or even melted.
For centuries, glass was made with flint or lead to create a beautiful, clear glass without impurities. Flint or lead glass will seldom discolor in the sunlight. In the late 1800’s, manufacturers created glass mixes that used magnesium instead of lead to create a brighter glass. In time, it was discovered that glass containing magnesium would turn lavender after months of exposure to the sun. Manufacturers replace the magnesium in the formula to selenium, to avoid this problem.
“Sun-purpling” became a widespread practice, especially in the Southwest where sunlight is plentiful. Glass dealers would expose their antique glassware to strong sunlight, in an effort to convince their customers that their glass was indeed antique, or made prior to 1915, when most manufacturers switched from magnesium to selenium. As the demand rose among collectors, prices increased, and the dealers needed a way to create sun-purple glass quickly.
Old glassware was exposed to germicidal black lights. Depending on the chemicals in the glass mix, the UV radiation from the light will artificially turn the glass a washed-out purple in a few weeks. Collectors may be told that this is a “newly-discovered” color in their pattern. Novice collectors might find this discolored glass and its apparent age charming, without realizing that it is damaged glass with little collectible value.
Not all light purple glass is a deception. Some is manufactured intentionally. Arcoroc has a line they call “Antique Amethyst”. L. E. Smith created reproductions of antique glassware in the color of sun-purple.
Collectors who are not aware of the effects of sunlight on the color of certain types of glass may leave their collection in a sunny spot, where it will discolor over time. Old glass that contains arsenic, which was used before WWII, will turn yellow with long exposure to sunlight. They are not purposely trying to damage their collection, but they may end up with a collection of devalued glass, equal to a collection of glassware that is badly cracked and chipped! Your glassware should be used and loved, but take care to keep valuable glassware out of the sun.