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Subject: Clear adhesives

Clear adhesives

From: Stephen Koob <koobsp>
Date: Wednesday, March 6, 2002
Robert K. MacDowell <macdowell_r [at] mediasoft__net>

>Does anyone have thoughts on an absolutely crystal-clear adhesive
>that would be suitable for bonding glass, ceramics and other objects
>where the bond line needs to be and remain very unobtrusive.
>Since around 1975, we have used Hysol (or Dexter) 608 Epoxy,
>For slow setting, we have been using Hysol 0151 Epoxy, which is a

Perhaps you do not need to change your "system", but it is time that
you changed your choices of epoxies.

There are some excellent epoxies that are currently in conservation
use for the repair and restoration of clear glass. If you really
want your "crystal clear" adhesive to be unobtrusive, you need to
consider both the Refractive Index (RI) of the glass you are bonding
and the RI of the adhesive that you are using.

Here are the several epoxies used by conservators in the U.S.:

    Epotek 301, RI 1.538-1-540, sets in 4-8 hours, depending on room
    temperature, hard enough to sand, polish in 12-18 hours.

    Epotek 301-2, RI 1.564,sets in 18-24 hours, hard enough to sand
    in 36-48 hours.

    The Epoteks are available from:

        Epoxy Technology
        14 Fortune Drive
        Billerica, MA 01821-3972

    Hxtal NYL, RI  1.51, sets in 24-36 hours, hard enough to sand in
    48-60 hours.

    Hxtal is available from

        Conservators Emporium
        100 Standing Rock Circle
        Reno, NV 89511

Several notes:  The Refractive Index of Hxtal is considerably lower
than that of the Epoteks, which makes it more appropriate for
ancient glass, and general silica-soda-lime compositions.  For
leaded glasses, which have a high RI, you will probably obtain a
better match with the Epoteks. You will need an analytical balance
for weighing out the resin:hardener ratios. These epoxies are very
sensitive to correct mixing proportions. All the epoxies will
eventually yellow, but the Epotek 301-2 and Hxtal have been
extensively tested and should give a clear bond for 50-100 years.
These epoxies have very low viscosities and can be somewhat
difficult to master.

You might look up a short article by Sidney Williston, in the
American Institute for Conservation Newsletter, Feb, 1983, p. 12 on
"Epoxy Hxtal, NYl-1", for some tips on applications.

Stephen Koob
The Corning Museum of Glass
One Museum Way
Corning, NY 14830
Fax: 607-974-8470

                  Conservation DistList Instance 15:61
                 Distributed: Wednesday, March 6, 2002
                       Message Id: cdl-15-61-002
Received on Wednesday, 6 March, 2002

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