Making a Point

This rather fabulous spearhead was discovered during excavations at Perth High Street in the 1970s. It is probably 12th century in date, perhaps related to the early years of the Royal Burgh.

Before our conservators could treat the spearhead, they needed to remove the old lacquer by soaking the whole thing in acetone. Corrosion and soil deposits were then removed using hand tools and swabs moistened with solvents. The spearhead was then immersed in alkaline sulphite solution for 12 weeks with regular changes of solution. This immersion technique is a method of stabilising archaeological ironwork; it helps remove chlorides which can often cause corrosion of archaeological iron. The spearhead was then rinsed in deionised water and then in solvents to dry the metal out thoroughly. Finally, the metal surface was pacified by with tannic acid. The acid reacts with unstable iron compounds to form a stable, protective layer on the object’s surface, which prevents corrosion.