As an objects conservator with many years of experience I would NOT
suggest that you use hot water or an ultraosnic unit with historic
coins or coins from antiquity.

Where do I start?

Well, first, hot water often changes the appearance of polished copper
alloys, and in every metal but gold water initiates corrosion - there
there are any salts present in the corrosion crust of the coin then
those salts will efflourece and can lierally tear the matrix of the
coin apart. Historic and ancient silvers are prone to an inherent
phenomenon known as discontiuous precipitation - the copper in the
alloy is internally displaced to the grain boundries of the alloy
leading to severe embrittlement. A fragile silver object can literally
crumble to pieces in your hands. I just finished the conservation of a
precolumbian silver beaker that had this problem and with the lightest
touch you would hear a high pitch tinkling and feel pieces crack and
move. Gold, if realatively pure, is liable to be in the best condition
because of its resistence to corrosion and oxidation.

Ultrasonic cleaning has very limited and specific uses in the cleaning
of historic and ancient metals. A true ultrasonic tank work with
tranducers that produce pressure waves in specific shapes and range of
frequencies. In a liquid medium these waves produce cavitation - which
is a process in which the air bubbles in the liquid implode. These
microbursts create extremely intense localized mirco-events that
create high temperatures and pressure that literally scour a surface
and its recesses and cavities. An object has to be totally sound in
order to be even conisder for ultrasonic cleaning. I have seen metal
objects loose all of their  patina and also develop cracks and etching
from ill conisdered cleaning in al ultrasonic tank.

I would first ask why there is such a rush to attempt to clean these
coins right now? If there is not some overriding need then leave them
alone until a professional conservation can do a condition survey and
some testing, to ascertain the safest way to deal with the issues
here.

If you need a few taken care of for an exhibit or loan then try to use
coins where cleaning is not a paramount issue, otherwise, again get a
skilled conservator invovled.

There is often a price for the practices of the past in any collection
and many of my colleagues well know that old adhesives are one of the
most common ones we encounter.

Cheers!
Dave

David Harvey
Conservator
Los Angeles, California

On 4/24/07, Paul Callomon <[log in to unmask]> wrote:
> Hi George,
>
> It depends on what kind of glue it is. If it's still sticking to metal
> after some time, then it's probably not PVA. Hardened Gum Arabic and
> other natural mounting glues like Casein would probably fall off if you
> dropped the coins into boiling water for a moment. You might also try
> ultrasound, in a bath of warm water.
>
> PC.
>
>
>
> Paul Callomon
> Collections Manager
> Malacology, Invertebrate Paleontology and General Invertebrates
> Department of Malacology
> Academy of Natural Sciences
> 1900 Parkway, Philadelphia PA 19103-1195, USA
> Tel 215-405-5096
> Fax 215-299-1170
> Secretary, American Malacological Society
> On the web at www.malacological.org
>
> >>> George Harris <[log in to unmask]> 4/24/2007 2:21 pm >>>
> Hello,
> I have just gone through a couple thousand coins and many of them have
> glue on one or both sides from when they were glued to something in an
> exhibit.  Does anyone know of an archivally safe way of removing this
> glue?  Some of it has come off easily with some slight proding, but
> much
> of it is still seriously glued and scraping it off would most likely
> result in irreversable damage to the coins.
>
> Thanks.
>
> Beau
>
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