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<div class="moz-cite-prefix">Dear Ian,<br>
<br>
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.<br>
<br>
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.<br>
<br>
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).<br>
<br>
Hope this helps<br>
Dirk<br>
<br>
<br>
Am 05.01.2017 um 00:19 schrieb Ian Hart:<br>
</div>
<blockquote
cite="mid:CANFVhtZm2FVrrdxS1JsBzE7Ttz+ofs_WTdxJTuh_8t03BvwuBA@mail.gmail.com"
type="cite">
<div dir="ltr">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.
<div>
<div><br>
</div>
<div>Has anyone experienced cracks like this? If so, were you
able to find out what caused them?</div>
<div><br>
</div>
<div>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)</div>
<div><br>
</div>
<div>I would gratefully appreciate any relevant information
you have to share on this subject.</div>
<div><br>
</div>
<div>--- <br>
</div>
<div>
<div>
<div class="gmail-m_-3439578652065454935gmail_signature">
<div dir="ltr">Ian Hart
<div><br>
</div>
<div>Preparator</div>
<div>Exhibit Studio</div>
<div>California Academy of Sciences</div>
<div>55Music Concourse Drive</div>
<div>Golden Gate Park</div>
<div>San Francisco CA 94118</div>
<div><a moz-do-not-send="true" href="tel:%28415%29%20379-5879" value="+14153795879" target="_blank">(415)
379-5879</a> </div>
<div><br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
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Dirk Neumann
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