Gina,

I encounter this issue often. Objects conservators are always
presented with ceramics and other objects that someone "fixed" many
years before with no records or documentation (and folks often wonder
why conservators write treatment reports!:-)

If there is a loosened sample of the adhesive, or maybe a generous
drip that you can carefully remove from a join, then you can test it
in simple solvents to see what will solubilze, soften, or swell the
old adhesive.

You can also examine some of the mended pieces with a ultraviolet
light (black light) in a dark room (such as a bathroom or closet). If
the adhesive has a distinctive orange color, for example, you are
probably looking at an old shellac.

Now, as far as using solvents - you need to use very small amounts
with lots of venitllation. I would test using things like distilled
water, acetone, denatured alcohol, and xylene (but try to avoid xylene
if possible as it is a more toxic solvent than the others). Once you
find a solvent that works, then I would apply it via a syringene or
other small container that will let you feed a small mount right into
the mend (I like those small glue bottles used by cabinet makers and
are in hobby shops), cover with saran wrap, and repeat, testing the
softeness of the join with firm but gentle flexing. Once a sherd lets
go and releases then you will have to continue this same way to soften
and remove the remainng adhesive and using a scaplel to carefully pick
it off of the break edge.

This is work that takes infinite patience and no small measure of hand
skill to do properly.

Once the old adhesive is removed, check the registration of the break
edges. You can re-mend using a much more revesible adhesive such as a
50% solution oif Acryloid B-72. For very large ceramics or heavy
ceramics, you can consider using a more dilute soution of the Acryloid
to isolate the break edges and then using a higher strength epoxy for
the mend - this will allow the mend to be reversible. Use a sandbox
for mending and it is wise to also wrap saran wrap around the sherds
that go into the sand to reduce abrasion (especially important on
softer earhtenwares). Do not use your adhesive as a fill material. Use
dots or a line of it in the center of the sherd but do not use an
excess to where it squeezes out filling the seam and also getting on
the body.

Again I warn you that this is not an easy thing to do well. Before
working on real artifacts I would suggest practicing on flea market
finds, buy something broken (if possible) and then drop it. Now you
have a group of sherds to mend!

Cheers!
Dave

David Harvey
Conservator
Los Angeles, California




On 9/5/07, Gina Gage <[log in to unmask]> wrote:
>
>
> Hi,
>
> I am a volunteer at a small historical museum. We have several pieces of
> prehistoric pottery that previous volunteers glued together. We want to
> unglue them, but do not have any information on the type of glue they used.
> Any suggestions would be most welcome!
>
> Thank you
>
> Gina Gage
>
> Gina S. Gage
> Project Director
> Historic Archaeologist
> Northland Research, Inc.
> 1865 E. 3rd Street
> Tempe, AZ 85281
> Office (480) 894-0020
> Cell (602) 339-0933
> Fax (480) 894-0957
> [log in to unmask]
>
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