[Nhcoll-l] FW: More on jars

[Callomon,Paul]

Hi Rob,

I've occasionally seen glass vials weakened to the point of fracture by glass disease. We illustrated one in Collections Forum 26 (1-2): 35, fig. 3.

PC

Paul Callomon
Collection Manager, Malacology, Invertebrate Paleontology and General Invertebrates
________________________________
Academy of Natural Sciences of Drexel University, Philadelphia
1900 Benjamin Franklin Parkway, Philadelphia PA 19103-1195, USA
callomon at ansp.org<mailto:callomon at ansp.org> Tel 215-405-5096 - Fax 215-299-1170



From: Robert Waller [mailto:rw at protectheritage.com]
Sent: Thursday, October 29, 2015 3:46 PM
To: Callomon,Paul; NHCOLL-L
Subject: RE: [Nhcoll-l] More on jars

Hi Paul,
There is not really a "difference in pressure between the internal structure of the glass and the external environment". In both cases, ambient RH or fluid preservative, alkali cations (Na+, Ca+) are leached out of the glass and replaced with H+ from the water. There will be a gradual migration of alkali cations toward the surface and a gradual counter migration of H+ inward (charge balance must always be maintained). There is no "pressure differential" between outside and inside of the glass - at least not due to alkali migration.

Is it important at all?
We are exchanging Na+, Ca+, from the glass in exchange for some H+ from the solution. But that is, after all, what a buffer would do and we might choose to add a buffer purposely. I doubt there would be a situation where a soda lime glass would raise the pH of a preservative solution above neutral though I am open to being corrected on that if I am wrong and someone knows better. Myself, I don't think that this source of preservative solution composition alteration poses any significant risk to collection preservation.

The glass jar is eroded and weakened and this could be a concern. Still so long as the inside of the jar remains "wet" there will be a layer of hydrated glass (like on a pH sensing electrode) that will reduce the rate of reaction (like a tarnish layer can protect a metal). I would be surprised if there were a case of glass jar failure due to this cause, though again I am open to being corrected by anyone with experience of such a failure.

Best,
Rob

From: nhcoll-l-bounces at mailman.yale.edu<mailto:nhcoll-l-bounces at mailman.yale.edu> [mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Callomon,Paul
Sent: October 29, 2015 1:11 PM
To: NH-COLL listserv (nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>) <nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>>
Subject: [Nhcoll-l] More on jars

Folks,

So here's a jar question that perhaps someone has answered:
In "glass disease" the non-silicate components of, say, soda glass gradually leach out of the silicate matrix and onto the surface as hydrated compounds. This happens more where humidity is high, as water is involved in the latter stages of the reaction. In vials found in dry collections, the resulting compounds can be seen as droplets of moisture on the surface of the glass. They will be on both the inside and outside if the vial is only stoppered with cotton, allowing its internal humidity to be close to ambient.
Where the jar or vial is full of fluid, however, the values representing the difference in pressure between the internal structure of the glass and the external environment will differ between the interior and exterior. So the question is: will the rate of migration of the non-silicate compounds differ accordingly - that is, will they tend head for the outside of the jar, where the pressure differential is higher? The answer, if there is one, may have a bearing on the extent to which glass deterioration will contaminate the fluid in the jar.

Paul Callomon
Collection Manager, Malacology, Invertebrate Paleontology and General Invertebrates
________________________________
Academy of Natural Sciences of Drexel University, Philadelphia
1900 Benjamin Franklin Parkway, Philadelphia PA 19103-1195, USA
callomon at ansp.org<mailto:callomon at ansp.org> Tel 215-405-5096 - Fax 215-299-1170

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