Precipitate on natural history specimens

On behalf of the curator of the Cole Museum of Zoology in Reading
UK:

    We are undertaking conservation work of natural history
    specimens in liquid preservatives, many of which have been
    neglected for several years, sometimes decades. When topping up
    specimens stored in 4% buffered formalin, we have noted that
    sometimes a white precipitate forms. The pH of the old formalin
    is usually between 5 and 7 and the pH of the new formalin is
    neutral. This happens more frequently if we use formalin we have
    made up ourselves, rather than formalin purchased already
    buffered, although it has happened with commercial formalin as
    well. We suspect that we are seeing salt precipitation, but are
    not sure what exactly is causing this. Does anyone have any
    suggestions for what is happening?

Fred van de Geer
Conservator
The Museum of English Rural Life,
University of Reading, Redlands Road
Reading RG1 5EX
+44 118 3787373


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                  Conservation DistList Instance 21:33
                Distributed: Wednesday, December 5, 2007
                       Message Id: cdl-21-33-022
                                  ***