Bronze pieces from Maquiz

Protohistory and Colonisations Departement

 

bronce de Maquiz

Iberian culture. 4th century BC. Maquiz Estate, Mengíbar, Jaén
Inventory no.: 1970/54/1 and 1970/54/2
Media and technique: Bronze

 

Condition

On archaeological artefacts metal parts are usually made of two different metal elements used to form alloys, and one of the most common alloys is bronze, a combination of copper and tin. This alloy may suffer alterations caused by the combined action of various agents, the most important consequence of which is corrosion.

The Maquiz pieces present films of copper oxide spread uniformly across the surface, as well as copper carbonates. In this case, both compounds have formed protective patinas on the alloy that do not harm the metal. However, another type of compound is harmful and represents a conservation risk for metal objects: copper chlorides, which tend to appear on certain areas of the artefacts, though in this case their presence is localised. With regard to alterations, we must also note the insoluble salts that have formed on the surface and conceal part of the decoration, as well as the presence of encrusted grime. Both are indications that this piece had never been thoroughly cleaned before.

 

Treatment:

Essentially we gave the surface a mechanical cleaning to eliminate traces of dirt and insoluble salts, especially in areas where there seemed to be decoration underneath. This proved to be one of the most revealing steps in the restoration process, for as we cleaned we were able to document new iconographic elements in the engraved decorations, such as the tree which appeared on one of the pieces.
After the cleaning, we took the important step of treating the metal with a corrosion inhibitor to ward off attacks from external corrosive agents and limit the amount of water and oxygen absorbed by the metal surface. To this end, we impregnated the metal with benzotriazole (BTA) applied with a brush.
Once the inhibitor had been added, we applied a protective coat of microcrystalline wax with a varnishing pad to eliminate shiny patches and give the metal surface a uniform appearance.