from the Glass Encyclopedia
from the Glass Encyclopedia above: clear glass changed to purple If you are looking for Sun-changed Glass or Irradiated glass there is often some for sale on eBay. See what there is just now - click Irradiated glass
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"Sun-Changed" or Irradiated Glass: A short explanation "Sun-Changed" glass is glass that has changed colour because of exposure to strong radiation. The same effect can often be achieved over a very long period by exposure to strong sunlight. Arsenic was used in glass-making before the second world war (pre 1940) and to a lesser extent after that date. When irradiated or exposed to sunlight for a long time, this glass turns yellow. The effect can be seen in the headlamps of very old cars. Manganese was widely used before about 1930 to decolorise impurities from clear pressed glass. Some glassworks went on using manganese after that time and some may still use it today. When irradiated or exposed to the sun for many years, antique glass with manganese turns purple. There are other chemicals which have been used in old glass which change the colour of the glass when exposed to strong sunlight or irradiation. Particularly vulnerable to these color changes are depression era glassware, sulphide marbles, Czech perfumes bottles, cut glass and early American pressed and blown glass. There are very strong views held by some glass collectors and dealers who believe that deliberately causing colour changes with irradiation is fraud, or at best that it damages our heritage of old glass. The process is usually irreversible, or the attempt to reverse the process can produce other unpredictable colors. The issue is aggravated by the existence of workshops which will, for a price, deliberately expose a piece of glass to irradiation to change its colour. Click here to see Elaine Henderson's webpage devoted to condemning this practice. There is also a most informative webpage by Dwayne Anthony reporting the results of irradiating glass insulators, with pictures before, after, and after trying to reverse the process. According to an article in Antiques & Collectors Reproduction News (in December 1997) you can send a piece of glass to a laboratory to determine whether the glass color is created by chemical ingredients or irradiation. This cost in the region of $125-$250; but there could be problems with these tests in terms of reliability and because they need to remove some of the glass to test it. |
