Subject: 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 ***Received on Saturday, 31 July, 1999