Page 398 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

solution to avoid the necessity of making fresh solutions and disposing of the old ones, and the
solution eventually becomes pale green in color. Benzotriazole is potentially carcinogenic and
must be handled with care, which is an additional disadvantage to repeatedly making fresh BTA
solutions, yet the current research clearly shows that this is the most effective method.
I SAFETY ISSUES The hazards associated with benzotriazole
use are discussed by Oddy (1972,1974b) and by Sease (i978), who point out that according to Sax
(i976), BTA has manifested only moderate toxicity in animal trials. Other references to the same
animal tests report the results to be "equivocal," although the material safety data sheets of the
international German chemical company ICN state that benzotriazole is not a carcinogen. 34
Oddy (1972) recommends the following precautions for using BTA in the museum
laboratory:

Do not inhale any powder.
• Do not allow alcoholic solutions of BTA to come in contact with the skin.
Do not allow alcoholic solutions of BTA to evaporate to dryness.
• Wear rubber or polyethylene gloves when handling treated objects.
Clean all glassware after use.
• Never heat BTA solutions (the solid sublimes at 98 °C).
• Wear a face mask when spraying any lacquers containing BTA, such as Incralac.

One of the most difficult recommendations to follow in practice concerns the evaporation of
alcoholic BTA solutions. The solutions are very prone to crystallize thin films of BTA crystals
around beakers and containers, very quickly forming dry deposits that might present a hazard
i
in the laboratory f extensively used outside of a fume hood. Excess benzotriazole crystals may
also precipitate on the treated object and would need to be brushed away from the surface.

AMT as a Ganorkar and colleagues (i988) describe another corrosion
corrosion inhibitor inhibition system that is claimed to remove bronze disease at
the same time. The method uses 5-amino-2-mercapto-i,3,4-
thiadiazole, known as AMT, which is a heterocyclic ring compound with the formula
(NH 2 )CNNC(SH)S. It is a pale yellow solid that is soluble in hot water and ethanol. The reagent
was tested on fifteen corroded bronze coins dating to the Islamic period, around the fifteenth
century, from the Birla Archaeological Institute, Hyderabad, India. The coins were first washed
in distilled water, then immersed in 150 ml of 0.01 M aqueous solution of AMT. A pale yellowish
green, curdy precipitate formed on the cuprous chloride areas; after an hour, the coins were
removed and washed. This procedure was repeated under vacuum until no further reaction took
place. The MT appears to form a complex species with the cuprous chloride; in addition, the
A
formation of a polymeric layer on the bronze, confirmed by infrared studies, confers some over­
all surface protection.

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