Manufacture
The Golden hats known so far are made from a gold alloy containing 85-90% Au, circa 10% Ag and traces of Cu and Sn (< 1% each). They are made of seamless single pieces of gold leaf, hammered to a thinness between 0.25 millimetres (0.0098 in) (Schifferstadt) and 0.06 millimetres (0.0024 in) (Berlin). Thus, the cones are surprisingly light considering their size. The Ezelsdorf example, measuring 89 centimetres (35 in) in height, weighs only 280 grams (9.9 oz).
Because of the tribological characteristics of the material, it tends to harden with increasing deformation (see ductility), increasing its potential to crack. To avoid cracking, an extremely even deformation was necessary. Additionally, the material had to be softened by repeatedly heating it to a temperature of at least 750 °C (1,380 °F).
Since gold alloy has a relatively low melting point of circa 960 °C (1,760 °F), a very careful temperature control and an isothermal heating process were required, so as to avoid melting any of the surface. For this, the Bronze Age artisans used a charcoal fire or oven similar to those used for pottery. The temperature could only be controlled through the addition of oxygen, using a bellows.
Considering the tribologic conditions and the technical means available at the time, the production even of an undecorated Golden hat would represent an immense technical achievement.
In the course of their further manufacture, the Golden hats were embellished with rows of radial ornamental bands, chased into the metal. To make this possible, they were probably filled with a putty or pitch based on tree resin and wax - in the Schifferstadt specimen, traces of this have survived. The thin gold leaf was structured by chasing: stamp-like tools or moulds depicting the individual symbols were repeatedly pressed into (or rolled along) the exterior of the gold. Combs were also used.
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