Date:         Tue, 12 Nov 2002 08:56:34 -0500
Reply-To:     Conchologists of America List <CONCH-L@LISTSERV.UGA.EDU>
Sender:       Conchologists of America List <CONCH-L@LISTSERV.UGA.EDU>
From:         CHARLES F STURM <csturmjr+@PITT.EDU>
Subject:      Re: Glass disease clarification
In-Reply-To:  <f05100300b9f661e5a805@[203.167.170.23]>
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Follow-up on Glass Disease

Much of this is info is taken from a presentation by Paul Callomon at the
AMS Meeting, 2002 in Charleston, SC.

Glass disease is a deterioration of glass exposed to water and CO2
Non-silicate elements of the glass, such as sodium oxide, leach out, react
with water vapor and form alkaline solutions. Over time the glass weakens
and a white powder deposits on the glass.

The chemical reaction appears to be:

Na2O-SiO (soda glass)

Na2O-SiO2 + H2O  SiO(OH)2 + Na2O
Na2O + H2O  2 NaOH
2 NaOH + CO2  Na2CO3
Na2CO3 + 10 H2O  Na2CO3-10H2O (washing soda)

The washing soda is the powder that is the end product.

Note, that this process requires water (moisture) to develop. Also,
chemical reactions occur at faster rates at higher temperatures that at
lower temperatures. Therefore, the same controls to prevent Bynesian Decay
should also prevent or slow down the development of Glass Disease: keeping
a low relative humidity and temperature in the collection storage area.
Also, borosilicate glass is more stable that flint or soda-lime glass.
Unfortunately, it is also more expensive, but are not our collections
worth it?

A similar reaction may occur with the Potassium oxides in glass.

You cannot determine what glass you are using by looking at it. At least,
not that I am aware of. Some manufactures mark the glass, but this is
generally seen with scientific glassware not with home use stuff. Kimax
and Pyrex are two types of borosilicate glass. I believe that Wheaton 800
is also a type of borosilicate glass. Soda-lime or flint glass fluoresces
a yellow-green color when exposed to UV radiation, borosilicate glass does
not. This is the only easy test that I know of.

Lastly, I do not like the term Glass Disease. To me "disease" denotes a
bacterial or viral illness, or such. This is a chemical decay process. I
would prefer to make an adjective out of glass and use that with the word
"decay". Unfortunately, the adjective that I come up with is "glassine",
and it is not listed in the Oxford English Language Dictionary other than
for a substance such as glassine paper, which is not glass based. Any
linguists or English language scholars out there that are willing to help
a madman come up with a better name :-)

Hope this helps folks understand what Glass Disease is.


Regards,
Charlie
******************************************************************************
Charlie Sturm, Jr
Research Associate - Section of Mollusks
                     Carnegie Museum of Natural History
                     Pittsburgh, PA, USA

Assistant Professor - Family Medicine

csturmjr@pitt.edu