Technical Experiments 1: Producing a piece of silver foil

As an alternative to high karat gold foils fire-gilt silver foils have been used to produce the patterned Early Medieval backing foils. For my experiments, I needed a silver foil of a material thickness of 0,025 to 0,03 mm. My starting material was a sheet the size of 10×10 cm and a thickness of 1 mm. It was composed of 93,5% silver, 6,2% copper and 0,3% zinc. The authentic way to reduce the metal thickness would have been to draw down the material by forging. but to save time I decided to thin the sheet by rolling using a hand-operated rolling mill. The metal is worked in a cold state. It is primarily stretched in length. Because the process creates stresses in the crystal structure, the workpiece has to be annealed after several passes though the rolls: You have to heat it to a red state and then cool it down. Rolling the silver sheet to a material thickness of 0,03 mm would mean that its length expands up to 4 m! So repeated cutting off of smaller pieces was necessary. I started to roll the sheet immediately, reducing the distance between the rollers step by step, and I could go on until a material thickness of 0,1 mm was reached. Then the gap between the rollers couldn’t be made any smaller. So I continued sandwiching the silver between two copper sheets. During the whole rolling process the workpiece had been periodically annealed. The thinner the sheet became the greater was the danger of melting. Finally, I held two silver sheets, sizes 2,7×6,6 cm and 2,7×5,2 cm, of a material thickness of 0,03 mm in my hands, with some small stress cracks along the edges and both a little bit warped, probably because of an irregular roller pressure.

Fig.1: surface area melted during the annealing process, image field: 10,5×15,5 mm (photo: RGZM/Stempel)
Fig. 2: stress cracks along the edge of the sheet, image field: 8×12,6 mm (photo: RGZM/Stempel)


Lit.: E. Brepohl, Theory and Practice of Goldsmithing, Brunswick 2001.

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