Carol,
  I have preserved several brittle fossil shells with a compound called
Butvar 76 which is dissolved in acetone.  The shells seem none the worse
for the exposure to the acetone.  To the best of my knowledge CaCO3 is not
very soluble in the major organic solvents.  The question is whether the
varnish will resolubalize in the solvent. My advice, take some of the less
valuable shells and put them in some acetone, methylene chloride,
turpentine, etc. and see what happens.  By all means do this outside,
under a fume hood or in a well ventilated room.  I generally restrict my
using Butvar/Acetone mixture to the warmer months when I can leave the
basement windows and doors open all day to vent the area.  The Merck Index
would probable give you info on the solubilities of calcium carbonate in
different solvents.  If you do not have access to this book let me know, I
can look up the info when I get home.
  I'm interested to read about other suggestions.
 
Charlie
**************************************************************************
 
Charlie Sturm, Jr
Clinical Instructor - Family Medicine
  University of Pittsburgh School of Medicine
Research Associate - Section of Invertebrate Zoology
  Carnegie Museum of Natural History
 
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On Fri, 6 Feb 1998, Carol Boswell Simpson wrote:
 
> I had a phone call from a lady yesterday who heard about our shell club...she
> said she had lots of shells she and her husband had gotten in Panama back in
> the '60's.  She described a few shells that I recognized, and then asked if we
> would like to have them.  She said she didn't want to sell them.
>
> I told her we often have auctions, and also fill lamps with the profits going
> to our scholarship fund.  (I was so excited to get these Panamic shells!!!!)
>
> We've made plans to meet tomorrow and she'll give us the shells.  Before she
> hung up, she said, "I don't know if this makes any difference or not, but we
> varnished the shells."  (There went my balloon!)
>
> If there are any really good shells in this donation, is there any way the
> varnish can be removed without ruining the shells?  (I'm assuming it was clear
> varnish.)
>
> Carol
>