Methyl cellulose

We, at the Georgetown University Law Library, have recently been
experiencing an odd thing happening with our methyl cellulose.  We have
been mixing 4 teaspoons of methyl cellulose to 1 cup of water to get an
adhesive about the consistency of a very heavy cream.  Recently, after
this mixture has been made it begins to deteriorate and becomes thinner
and more watery.  This usual begins to occur after about two days.  We
have been using the same batch of cellulose, the same plastic containers
and the same utensils.  We had been using tap water and began to use
distilled water, hoping this might correct the problem but it did not.
We have also tried mixing and storing the mixed adhesive in a glass
container, this did not help either.

I am not absolutely sure what kind of methyl cellulose I may have
here.  It is at least 3 years old and was here when I took this position.  It
 was purchased from Bookmakers, Riverdale, Maryland and after speaking with
them I believe it is what they describe as the higher viscosity 4000 (A4M),
"premium grade of methyl cellulose (lower iron content)".  I do not believe
it is the 1500 (A15) used for sizing.

We are awaiting an order for more
methyl cellulose, but I have been told that methyl cellulose does not
have a limited shelf life.  Has anyone had a similar experience or any
ideas about what may be happening?  Thanks in advance for any help you
might be able to give.

Annette Morris
Preservation Librarian

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                  Conservation DistList Instance 6:40
                 Distributed: Friday, January 29, 1993
                        Message Id: cdl-6-40-011
                                  ***