![]() ![]() This certainly highlights how easily artifacts of the past can disappear and also how important what remains we do find are! ![]() I remember your interest in this topic during the Coins and Collections visit. Harry Anastopulos: Somehow I figured you'd pick this one, Evie. Keffie: Excellent and clearly explained summary of this phenomenon. The Journal of the American Institute for Conservation, Volume 29, Number 2, Article 7, 1990. Bronze Disease: A Review of Some Chemical Problems and the Role of Relative Humidity. However, the effects of bronze disease can be controlled with due precaution and careful periodic examination of artifacts. Unfortunately, humidity control is very costly, and sometimes impractical in a display setting. Below 39% humidity is ideal for bronze storage and display. Consequently the bronze disease is completely untreatable, and the artifact will be lost.Īn alternative to a finishing lacquer is some form of humidity control. Secondly, if the bronze disease hasn’t been completely eliminated, the metal will continue to corrode beneath the lacquer. ![]() Firstly, it is very difficult to reverse their effects without causing serious damage to the artifact. However, microcrystalline waxes are risky for two reasons. This method is favored by the British Museum. Once cleaned thoroughly, the piece can be coated in a varnish, wax or a resin to prevent a recurrence of corrosion. It can be dissolved in ethanol to make a solution for soaking infected artifacts. This complexing agent is highly carcinogenic. Again, this will only halt the reaction until the cuprous chloride comes into contact with moisture in the air.Ī more thorough solution to the bronze disease problem involves using benzotriazole (C6H5N3). Another non-permanent fix is soaking the afflicted piece in either distilled water or a solution of sodium carbonate and sodium bicarbonate. Additionally, this is certainly not a permanent solution just one more especially humid day and the bronze disease will be off and raging again. Unfortunately, this often causes the surface of the metal to darken irreversibly. This can be done by placing the infected coins or artifacts in the oven on low heat in order to dry them out. Initially, the reaction can be stalled by removing the moisture from the piece. Among private collectors, there are several popular methods of stalling the effects of bronze disease, though none of these are permanent cures. However, several steps can be taken to both prevent and treat bronze disease. If left untreated, bronze disease will continue to eat away at the metal to the point of complete destruction of the artifact. Generally, the fuzz covers pockmarks caused by the hydrochloric acid.Ī basic representation of the chemical process. This second equation produces the visual manifestation of the disease: that dreaded green fuzz. The acid then eats away at the bronze, and in turn reacts with the copper. However, the basic understanding of the process indicates that the presence of cuprous chloride in copper alloys reacts with water to create hydrochloric acid. The actual chemical reaction is still not fully understood, though the chemistry of corrosion has been studied for some 150 years. It might take just one humid day to activate the reactions and begin the destructive chain. Bronze disease is triggered by the presence of water in this equation. This corrosion is caused by a circular set of reactions that involve the chlorides of a copper alloy and water. This corrosion is much like rust on iron. It is known as bronze disease because the reaction produces a green powder on the surface of bronze artifacts that resembles a fungus. In reality, “bronze disease” is not the result of bacteria, as the name would suggest, but the result of a complex chemical reaction. However, while a patina is not destructive, bronze disease most certainly is. To the untrained eye, it may simply resemble a natural patina. It manifests itself as either a powdery green substance on the surface of the metal or as a warty or waxy film over the surface of an artifact. Bronze disease is a form of corrosion that affects bronze artifacts. ![]()
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