[Nhcoll-l] FW: More on jars

[Robert Waller]

Hi Paul,

Thanks for reminding me of those nice pictures.

 

I wonder though how much the glass disease issue contributed to the
breakage. Although a little difficult to make out in the pictures it looks
like the surface alteration of the glass is still very thin in relation to
the bulk of the glass wall. If that is the case then it might not be the
most significant cause of fracture - perhaps thermal stress from a
manufacturing flaw or just past dropping contributed. Have you ever seen
comparable fractures in vials not exhibiting glass disease? I suppose a 2x2
factor table relating count of fractured and not fractured vials with and
without glass disease would let us know. Sounds like a counting job for an
intern!

Rob

 

From: nhcoll-l-bounces at mailman.yale.edu
[mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Callomon,Paul
Sent: October 29, 2015 4:01 PM
To: NH-COLL listserv (nhcoll-l at mailman.yale.edu) <nhcoll-l at mailman.yale.edu>
Subject: [Nhcoll-l] FW: More on jars

 

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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