Spray adhesive

David Walker <david [at] talismanrestoration__com> writes

>Does anyone have experience using "workable" matte spray adhesive as
>a consolidant for the surface of very dusty, friable clay objects?
>Certainly it is not reversible for this application and may cause
>some darkening.  Are there other arguments against its use?

I would like to submit the following:Pneumatic sprays can have
several disadvantages. Firstly, the force required in order to
disperse the liquid adhesive into small droplets is high and imparts
a certain minimal velocity to these droplets, which may be too high
for fragile, friable surfaces, with the risk of causing smearing and
loss. As well it is difficult to minimize the quantity of adhesive
delivered with a pneumatic spray, because there's a minimal amount
that is needed for it to work.

Another problem is the concentration, which should not be too high
because higher concentrations are usually more viscous and may not
fully penetrate to the bottom of the friable layer to consolidate
the full depth of the layer; skinning may result, and possibly
darkening. As well it is not always realized that the spray
droplets, as they travel from the nozzle to the object, evaporate to
some extent; this means that the solution concentration is not the
same when the consolidant has reached the object.

I do not wish to discuss here the issue of darkening and PVC, but
encourage you to read further on it and on possible solutions (such
as using solvent-saturated atmospheres) in Hansen E.F., S. Walston
and M.H. Bishop, 1993, "Matte Paint, its history and technology,
analysis, properties and conservation treatments, with special
emphasis on ethnographic objects", Bibliographic supplement to Art
and Archaeology Technical Abstracts 30, Marina del Rey, California:
Getty Conservation Institute and International Institute for
Conservation. Let me just note that darkening can be caused by
applying too much adhesive, or at too high a concentration (besides
other factors which I do not want to get into- solvents, for ex.,
can have an effect), and as mentioned above, sprays can easily
deliver too much, or too high concentrations.

A possible alternative is the ultrasonic mister or the ultrasonic
nebulizer.  These were developed as a means of applying a
consolidant onto a friable surface (1) in a delicate manner (i.e. at
very low impact velocity), (2) as dilute solutions, and (3) in
controllable, minute quantities applied incrementally.  It can be
surprising how even minute quantities can often have a consolidating
effect.

For further info on the ultrasonic mister see: S. Michalski and C.
Dignard, "Ultrasonic MIsting Part 1, Experiments on Appearance
Change and Improvement in Bonding"  J.AIC 36 (1997) p. 109-126 ; and
C. Dignard, R. Douglas, S. Guild, A. Maheux and W. McWilliams,
"Ultrasonic Misting, Part 2, Treatment Applications", J.AIC 36
(1997) p. 127-141. Ultrasonic nebulizers are a later development to
the ultrasonic mister; they are sold by medical suppliers for asthma
control, for ex. DeVilbiss' Ultra-Neb; as well the Aerosol Generator
by Becker Preservotec is based on this system.

Carole Dignard
Objects Conservator
Canadian Conservation Institute
1030 Innes Road
Ottawa, Ontario, Canada, K1A 0M5
613-998-3721 ext. 151
Fax: 613-998-4721


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                  Conservation DistList Instance 16:18
                Distributed: Thursday, September 5, 2002
                       Message Id: cdl-16-18-009
                                  ***