Conserving
Copper-Alloy Objects
see also:
Coin Cleaning
Cleaning
bronze and Romana
Cleaning
Copper
Conserving
Advanced Cleaning
Many copper-alloy objects will remain stable when excavated, and
will require no particular conservation treatment. The application
of waxes or lacquers as mentioned previously may however aid protection
as well as improving the appearance of an object.
One of the most destructive threats to copper-alloy objects is
a condition known as bronze disease'. This can he recognized by
small areas of powdery green corrosion, which erupts from below
the surface of an object. This is caused by the presence of chlorides
which were sealed within the corrosion products. And which can become
active if the environment of an object is altered. This may also
occur when an object has been subjected to chemical or electrolytic
cleaning. Once it takes hold, bronze disease is a progressive form
of corrosion, which, if left unchecked, can totally destroy an affected
object.
The only solution is the removal of the affected areas. This can
he achieved either by totally stripping an object hack to hare metal,
with all its attendant disadvantages. Or by picking out any small
spots with a dental tool or adapted engraving tool. If any trace
of bronze disease is left, it will re-occur.
To conserve an object, either following the removal of bronze disease
or after any form of cleaning and/or toning, treatment with benzotriazole
(BTA for short) is now generally recommended. Before using BTA,
an object must first be degreased by Immersion in alcohol or acetone,
this should then be followed by a prolonged soaking in a solution
of caustic soda, which will reduce subsurface chlorides and better
prepare an item for treatment.
The next step is to remove the object and allow it to dry, after
which it should be placed in a 5% solution of BTA, dissolved in
alcohol, It should be left for several days. Then removed and once
again allowed to dry thoroughly. The final stage is to brush off
any loose precipitate that may have formed, and to then apply several
coats of a protective lacquer, preferably Incralac or another suitable
proprietary conservation lacquer. Domestic varnishes have additives,
which may be harmful in the long term. The BTA solution can be used
repeatedly, and only needs disposing of once itbecomes discolored.
THIS ADVICE WAS KINDLY GIVEN TO US AS GUIDE NOT A GOSPEL METHOD
OF CLEANING, YOU DO SO AT YOU'RE OWN RISK!!!!
|