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...to foster and encourage the collection, appreciation, study,
preservation, and documentation of early American pattern glassware, and its place in American life, past and present. |
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Does Flint Glass Sun Darken/Purple ?
| Steve & Radka Sandeman - |
Friday, November 9, 2007 |
| Does Flint Glass Sun Darken/Purple ? |
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Hi!
We know that Elaine Henderson & others, including us, absolutely HATE sun-purpled glass, and have a quick question along these lines. We recently found and sold on Ebay a Flint ASHBURTON Creamer in perfect condition; however, we just received a note from the buyer that this is sun-purpled; in our opinion, this was not at all purpled, but that's his claim. We were under the understanding that flint glass will not purple, due to the chemical components used in the manufacture of flint glass. We know that it's manganese that turns from exposure to sunlight, so is it possible that flint glass could turn?.....even slightly? If there's a specific reference we could point to, it would certainly help. We don't want anyone disappointed, but like to be correct in our statements.
Thanks Very Much in advance for your help!
Steve & Radka Sandeman
in (normally) Sunny San Diego |
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| Kat Krivda - |
Hi Steve and Radka,
Manganese, or "glassmakers soap" was used in various quantities as a clarifying agent for as long as glass has been made. The natural color of glass is dependant on the impurities in the glass batch and will normally have a green or brown cast (see early bottles). Manganese clarifies the impurities to make it clear. It's also the chemical that makes purple glass purple (depending on quantity). Clear Flint glass will turn, but because of the flint, or iron oxide, it will turn a grayish lavender. To answer your question: Yes, flint glass will turn. Not necessarily the way that soda lime glass will, and usually not artificially (it turns a really ugly color), the way some nefarious dealers have turned their glass "sun-purple", but it will turn.
As to where this information comes from, there is no one source, but several. English Glass for the Collector 1660-1860 by G. Bernard Hughes has a very good chapter on the beginnings of blown Flint Glass. George & Helen McKearin in their book American Glass give a fairly good accounting of glass making in the Americas along with an explanation of clarifying glass (page 9). The rest of the information comes from reading (a lot), and experience (what I've seen).
If the ASHBURTON glass you sent was absolutely clear, I hate to say it, but it may be someone trying to exchange their "sun darkened" piece for your clear one. You might tell them to send it back and refer to your "invisible" mark before sending their refund.
Hope this helps.
Kat
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