Heat-set adhesive

This is a reply to Rebecca Cameron, concerning Ademco "heat set
tissue".

The name Ademco replaced the companies original name which was the
Adhesive Dry Mounting Company, Limited.  They were originally a
British company, however last I heard they have merged or have been
bought by Seal, which is the major manufacturer of dry mount tissue
in the United States.  Ademco has long claimed to have invented dry
mount tissue, even though it was fairly easily made by coating paper
with shellac.  Which brings me to my first point.

Early dry mount tissues were indeed shellac coated on paper.  The
problem which has come from this is that there have been some
examples of photographs, when unmounted in alcohols (particularly
ethyl), developing pink/red stainings.  The belief,  is that  the
alcohol releases some of the lac dye which naturally occurs in
shellac and this stains the photograph. I usually recommend acetone
instead of alcohol for removing these tissues because at this time I
know of no  instance of a shellac dry mount tissue staining a
photograph when unmounted with acetone.  (If anyone does, please let
me know.)

The recommended solvent for unmounting Ademco tissues in the mid
80's was IMS.  You tried that and it did not work.  If this adhesive
happens to be similar to the Seal tissues, you might try benzine.
You also might try contacting Ademco, they were once based in
London.  One of their tissues was an adhesive without a paper base.
That may be what you have.

The best paper on early dry mount tissues that I am aware of is:

    "Origins and Development of Dry Mounting", Stephanie Watkins,
    The Book and Paper Annual, Vol. 12, 1993.  (AIC).

Marion L. Hunter, Jr.
Conservator of Photographs and Works of Art on Paper
Charleston, SC

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                  Conservation DistList Instance 13:11
                   Distributed: Friday, July 30, 1999
                       Message Id: cdl-13-11-011
                                  ***