Heat-set adhesive

Without getting into too much debate about who invented what,
natural vs synthetic adhesives, the following background (from my
head, not from the archives) may be of interest.

We first became aware of our 105 Lens Tissue being used for this
purpose in the 1960s. The whole approach had a huge boost (sadly)
from the Florence floods when Roger Powell, Tony Cains and Peter
Waters were having substantial quantities shipped over which they
were coating themselves. It is probably at about that time that
Ademco starting producing conservation versions to add to their
existing range of commercial photographic dry mounting tissues. (The
latter I think originally based on hard tissues impregnated rather
than coated). In the 1970s 105 was replaced by an improved version
called L2 (since replaced by LZ). The main difference was that 105
(or L) tissue was about 70% abaca (manila hemp) and 30% softwood--a
blend that was quite acceptable for lens cleaning (for which we had
had it made since the 1930s) but we felt that a 100% abaca tissue
would be better for conservation. This tissue is made to our
specification by Cromptons hence the rather confusing expression
"Crompton tissue" used by many people. (Confusing because Crompton
make a huge range of tissues for teabags, sausage casing, electronic
and medical wipes etc).

Ademco developed improved adhesives which were coated onto the
tissue, initially using organic solvents for the adhesives. It may
not be widely appreciated how difficult it is to coat a very thin
absorbent tissue without penetration (which can lead to blocking).

Meanwhile Cains and Waters had moved to Trinity College, Dublin and
Library of Congress, Washington DC respectively where with various
colleagues improved versions of the original hand coated tissues
were developed particularly using various blends of acrylic resins.
The general technique is to coat glass or a polymer film with the
adhesive/water emulsion and lay the tissue on when tacky. Again
there are many things that can go wrong so this is a skilful and
costly process. It is mainly done in house but can be obtained
commercially from

    Bookmakers (Cindy & Frank Mowery)
    6001 66th Ave
    Riverdale MD 20737
    +1 301 459 3384
    Fax: +1 301 459 7629

using LZ tissue. They could no doubt advise on the current views on
adhesives.

Ademco at one stage switched to using acrylic/water emulsion coating
using resins recommended by leading conservators. Unfortunately in
the 1980s a variety of polymer suppliers, coaters and paper
merchants came on the scene marketing what they claimed were as good
as the original materials but which some times turned out to be
Modelspan (an aircraft covering tissue, melamine hardened and never
offered by the makers as being suitable for conservation), or
various types of adhesive which lead to questions on discolouration,
lack of reversibility, blocking etc. Some of these companies have
disappeared, others have re-emerged with new names--none of which I
shall mention!

We have not had much contact with Ademco since they were taken over
by Seal and no doubt they could provide up to date information from
the address recently provided

    Ademco Ltd
    Lincoln Road
    Cressex Estate
    High Wycombe
    Buckinghamshire HP12 3QU
    +44 1268 530331

This incidentally is the address that they had from at least the
early 1970s).

LZ tissue continues to be made for us by Cromptons from 100% abaca,
alkaline cooked and unbleached. We supply it to national archives &
library and specialist importers around the world. Most are applying
adhesive in house. One major user still employs cellulose acetate
film and has difficulty getting it. What is the current view on this
material? For that matter what is the general view on the safety
aspects of using acetone? It's not a material I would want to have
close or regular contact with!

Simon Barcham Green

                                  ***
                  Conservation DistList Instance 13:12
                 Distributed: Wednesday, August 4, 1999
                       Message Id: cdl-13-12-002
                                  ***