[Nhcoll-l] crack formation in glass stoppered jars on display

[Dirk Neumann]

Dear Ian,

it seems that this is the typical damage that happens if ground stopper 
jars are exposed to temperature shifts: of the temperature climbs 
slightly, the neck widens and the stopper gets slightly deeper into the 
neck. If it gets cooler again and the neck tightens again, tensions 
builds up inside the neck and which causes the cracking you observed.

Suited (silicone free) grease might help to minimise the observed 
problems, but it would be good to reduce temperature fluctuations inside 
the cabinet. Also, check for and heat radiation that might be caused by 
the light sources inside the cabinet, which could add to the problem.

Such problems could be increased if the stopper jar is of low quality 
(e.g. poor soda-lime jars that have been produced shortly after WW II), 
as these already have poor glass quality, or - because they were cooled 
down too fast during production - still have sufficiently high tensions 
inside the glass; both adds to the problems you observed. High quality 
borosilicate jars might be a suited alternative (e.g. Dixon or Stoelze 
Oberglass).

Hope this helps
Dirk


Am 05.01.2017 um 00:19 schrieb Ian Hart:
> We have had tadpoles (mounted on glass slides) on display in old 
> ground-glass stoppered jars containing 10% formalin since September 
> 2014. In the last 6 months (of 2016) two of these jars have developed 
> (apparently) spontaneous cracks in the neck of the jar. Nothing could 
> have struck the jars from without.
>
> Has anyone experienced cracks like this? If so, were you able to find 
> out what caused them?
>
> We want to put the specimens back on display, but would like to rule 
> out the display environment as a contributing factor to the cracking 
> problem. The jars are on display in an illuminated cabinet. We do not 
> have case temperature data for the time that the cracks occurred, but 
> we have subsequently recorded a maximum daily temperature fluctuation 
> in the case of 4.25 deg F (from 70.803 deg F to 75.075 deg F)
>
> I would gratefully appreciate any relevant information you have to 
> share on this subject.
>
> ---
> Ian Hart
>
> Preparator
> Exhibit Studio
> California Academy of Sciences
> 55Music Concourse Drive
> Golden Gate Park
> San Francisco CA 94118
> (415) 379-5879 <tel:%28415%29%20379-5879>
>
>
>
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-- 
Dirk Neumann

Tel: 089 / 8107-111
Fax: 089 / 8107-300
email: Dirk.Neumann(a)zsm.mwn.de

Postanschrift:

Staatliche Naturwissenschaftliche Sammlungen Bayerns
Zoologische Staatssammlung München
Dirk Neumann, Sektion Ichthyologie / DNA-Labor
Münchhausenstr. 21
81247 München

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---------

Dirk Neumann

Tel: +49-89-8107-111
Fax: +49-89-8107-300
email: Dirk.Neumann(a)zsm.mwn.de

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Bavarian Natural History Collections
The Bavarian State Collection of Zoology
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Muenchhausenstr. 21
81247 Munich (Germany)

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