[NHCOLL-L:2433] Re: Evaporation, taping of jars

[Paul Callomon]

Hi Gayle,

Plumbers' tape is supposed to be applied to threads before a joint is closed. As the joint is screwed shut, the tape 'smears' and fills the fine gaps on the non-pressure-bearing face of the thread. It is good enough at this to make water- and even gas-tight joints (though it's not approved for domestic gas, for which liquid compound is used). It should not work on glass jars, though, as the gaps in the threads are in the order of hundreds of microns, rather than tens. Pipe threads with tape are themselves impermeable, whereas the threads on a glass jar are just a mechanical device to push the sealing disk down against the rim.
In our collection, however, the tape was wrapped around the outside of the jars. Teflon tape stretches slightly and wets any smooth surface, so at first glance this gives the impression of a good seal. Any proud irregularity (one that sticks out of the surface, like a molding rib, as opposed to a pit or scratch), however, cannot be sealed by a tape that is stretched over it, unless the tape were somehow capable of expanding at right angles to the direction of stretch. Of course, though, when you stretch tape its width contracts. This is why I think a non-stretched tape with an adhesive that fills gaps (such as medical sticky bandage) will work much better.
I suspect your good results have more to do with the quality of your primary seal (within the lid) than the application of tape to the threads. You can find out; remove the sealing disk from a lid, and then screw it back on with just the tape. If the fluid does not evaporate, your tape is sealing. If it evaporates more slowly than a jar with no disk and no tape, then the tape is sealing partially.

Regards,

PC. 


Paul Callomon
Collections Manager
Malacology, Invertebrate Paleontology and General Invertebrates
Department of Malacology
Academy of Natural Sciences
1900 Parkway, Philadelphia PA 19103-1195, USA
Tel 215-405-5096
Fax 215-299-1170
Secretary, American Malacological Society
On the web at http://erato.acnatsci.org/ams/


>>> "Gayle" <gaylehansen at harborside.com> 09/27/04 02:08PM >>>
Hi folks,

I have used Teflon tape to seal glass jars filled with 5% Formalin in
seawater & algae for 35 years now with no leakage.  I run the tape around
the screw threads of the glass jar twice and then screw the lid (generally
bakelite so they don't rust) down over them.  It seems to work fine.
However, everytime you unscrew the jar, you have to add more tape.    Is
this how you are using it?

I have heard that the Teflon jar cap liners (quite expensive) work just as
well -- but they are out of my budget.

Gayle Hansen
Hatfield Marine Science Center
Oregon State University
Newport, Oregon 97365


----- Original Message -----
From: "Paul Callomon " <callomon at acnatsci.org>
To: <dwood at sdnhm.org>
Cc: <NHCOLL-L at lists.yale.edu>
Sent: Monday, September 27, 2004 10:25 AM
Subject: [NHCOLL-L:2431] Re: Evaporation, taping of jars


> Hi Dustin,
>
> My predecessor as collections manager spent months wrapping plumbers' tape
(Teflon tape) round each of about 25,000 jars in our alcohol collection.
Unfortunately, she did not check the condition of the lids first, and I have
found dozens of old metal lids happily rusting away under their bright new
tape covering.
> As far as I can tell, taping up jars in this way does not help much. If
vapor has made it past the initial seal, then tape may or may not trap it
The principle is that the tape provides a secondary barrier to vapor escape,
but this assumes a very clean, tight seal against both the jar (which must
thus be free of molding marks) and the lid (which should thus not be
knurled). In practice, most collections contain a combination of lid and jar
types. For us, any reduction in vapor release that taping might have
achieved has not justified the considerable time taken to apply the tape and
the difficulty I now have in visually assessing the condition of older metal
caps. Instead, I have bought a big box of new lids in each of the sizes we
use, and apply these to older jars every time I find one that is leaking.
> I guess if you used a tape whose adhesive had good bridging qualities,
such as medical adhesive bandage (which we use for jar labels, with great
success), then taping up lids would work better.
>
> Regards,
>
> PC.
>
> Paul Callomon
> Collections Manager
> Malacology, Invertebrate Paleontology and General Invertebrates
> Department of Malacology
> Academy of Natural Sciences
> 1900 Parkway, Philadelphia PA 19103-1195, USA
> Tel 215-405-5096
> Fax 215-299-1170
> Secretary, American Malacological Society
> On the web at http://erato.acnatsci.org/ams/ 
>
>
> >>> "Dustin Wood" <dwood at sdnhm.org> 09/21/04 05:37PM >>>
> Dear Paul Callomon,
> I got your email off the nhcoll-list serve from a discussion on taping the
> outside of fluid-filled jars to take an extra step in preventing
> evaporation.  I'm interested in the product you use for sealing the
outside
> of the jars?  I've noticed some evaporation on some of our new jars/lids
> (even with foam-backed Teflon liners) and would like to take the extra
> precaution.  Thanks in advance for your help.
>
> Dustin
>
>
> Dustin Wood
> Collections Manager
> Department of Herpetology
> San Diego Natural History Museum
>
> 1788 El Prado
> San Diego, CA 92101
>
> Phone: 619.255.0305
> FAX: 619.232.0248
> Email: dwood at sdnhm.org 
>
>