How it all got started--
   Lead has been used for centuries as a clarifying agent in making glass. In the 1860's the formulas for American pressed glass changed & lead (See article on flint glass) began to be removed from the mix & manganese was substituted to make the glass brighter and to act as a stabilizer.
    In time, it was noticed that this glass made without lead but containing manganese was found to turn a very light lavender if placed in a sunny window or otherwise exposed over time to (ultraviolet) rays of the sun.
    At some unknown point, antique dealers, no doubt beginning in the "Sunny Southwest", learned that by setting their old glass out in the sand, on their rooftops, or wherever they could get a sunny exposure, they could turn the glass REALLY purple. If they set glass out and it turned purple, it proved to them and to their customers that the glass was, indeed, made prior to ca. 1915 when most, but not all, glass companies ceased using manganese and substituted selenium as the clearing agent. Heisey, Duncan & Miller, Fostoria, Cambridge and Imperial glass companies are some exceptions.
       But purpling glass in the sun took months to accomplish, even in our bright SW sunshine. As the demand by folks (who had no idea they were being sold ruined antiquities) for "sun-purpled" glass and the prices realized by the purpling dealers increased, an effort to speed up the purpling process was made. Because germicidal lamps emit ultraviolet rays which simulate those of the sun, great numbers of people began to buy glass that glowed yellow under a black light (see article), and subject the glass to the germicidal lamps (which didn't set in the western skies in the evening wasting all that valuable purpling time).
   The artificial process is so simple and the financial rewards are apparently so great that the practice has spread and grown to the extent that thousands and thousands of pieces of EAPG have now been turned purple and put on the public market.
                        The color change to purple is irreversible.
  Following is an article first published in The Antique Trader, July 1994.
This Color Purple--
          An Unnatural Disaster
   There is a dilemma in the world of Early American Pattern Glass that needs addressing. It is the widespread practice, in the southwestern United States, of exposing EAPG to a germicidal black light for a few weeks or directly to the sun for an extended period of time thus turning the glass artificially purple. The merchandising MO is to buy old glass, do the exposure thing, take the pieces that turn a pukey light purple (some flint won't turn), hike up the price, write a little purple flyer with a charming story about how the sun, over the past hundred years has reacted with a chemical, "magnesium" (sic), in the glass and created this glorious purple antique.
  This is not a small problem. We have seen booths in California, Arizona and New Mexico with hundreds of pieces of EAPG ruined for eternity in the name of, well, greed. The process is irreversible. Call us supersensitive perhaps, because our business is EAPG pattern-matching and no one wants a set of dishes with a purple spooner, but the sight of a shop full of this stuff turns my stomach!  My analogy for the rest of the antiques world is that this practice is tantamount to taking an original Pennsylvania Dutch painted chest, stripping it down, repainting it red, white & blue striped and calling it patriotic.
    To be fair, some dealers who have a few purple pieces are genuinely surprised when we reject their pieces and tell them they are ruined, but I have spoken with a number of people who own shelves-full of this glass- none of whom admit to having been the one to "do the deed", and their response is always defiantly, "It sells." They say (ignorant) visitor's from "up north" are enchanted with the idea of the age of the glass and its being affected by our fabulous southwestern sun.

 This, in the face of out and out admissions that a germicidal UV lamp was actually used & the sun had nothing to do with it!
  Bill & I have done what we can; we leave little notes in pieces that say "Please stop turning EAPG purple!"; try to reason with the sellers that there is a finite amount of this antique glass available & suggest they just carry a line of purple glass & tell customers it used to be clear, etc (that would be no more deceptive & a lot less destructive).

Even at Flea Markets it is
FEATURED
in some booths-		  Obviously we EAPG dealers have done a poor job of selling the original charm of our merchandise & that also needs to be remedied.
     Meanwhile, with full understanding that all sellers are free to do whatever they want, to whatever they own, we beg, beseech & implore members of the professional Antiques community to join with us in denouncing this practice, rejecting any pieces that have been ultraviolentedly tampered with and doing whatever is possible to educate the buying public that EAPG is beautiful, useful and charming just as it was created two centuries ago.
   Jerry Greenblatt has well put the dastardly practice in perspective:
     "People who change the color of glass objects must have had no regard for them, since they are no longer what they were. Making them purple is like painting them gold or adding attractive cracks. That old article uses glass chemistry to justify altering color, as if clear glass is like photographic film that must be developed to see what was within. Think of what might emerge by irradiating colored glass! Think of the abstract images that might emerge by using a blowtorch on the Mona Lisa!"
"Oh NO!!!"