the Glass Encyclopedia
the Glass Encyclopedia
 above: clear glass changed to purple
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Irradiated Glass: A short explanation Irradiated 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 deep 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. If you are looking for irradiated glass, you may find items amongst the purple glass on offer on ebay (click here to look through the purple glass listings on ebay). |
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There are some very strong views held by glass collectors and dealers. Many believe that deliberately causing colour changes with irradiation is fraud, and others are upset that it damages our heritage of old glass. The process is usually irreversible, or at best 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.  References & Bibliography: 1: "Changing Glass Colors with Irradiation" in Antiques & Collectors Reproduction News (December 1997) 2: "This color purple - an unnatural disaster" in The Antique Trader, July 1994 by Elaine Henderson 3: "Altered Glass Colors" by Phyllis Petcoff 4: "Fake and Altered Insulators: Artificially Induced Colors" by Dwayne Anthony . Books on EAPG Glass 1: Early American Pattern Glass, by Alice Hulett Metz, 2000. 2: The Collector's Encyclopedia of Pattern Glass by Mollie Helen McCain, 1983 3: Collectors Guide to American Pressed Glass 1825-1915 by Kyle Husfloen 1992 4: A Complete Guide to Pressed Glass by Bob Batty, 2000 Click on the picture below to read more about any of these books, including price and any available discounts for buying on-line. 
If you have never tried an on-line auction, explore ebay, - still the best! Type what you are searching for in this box: FIND GLASS on ebay! Take a quick look at your kind of glass in Angela's Designer Searches - save time and don't miss an opportunity even when you are busy! - CLICK HERE INFORMATION about Bagley Glass!
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