To gild Middle Ages sculptures, artists frequently applied extremely thin gold foil supported by a silver base layer.

As specified in a Phys.org report, for the first time, scientists at the Paul Scherrer Institute PSI have managed to create nanoscale 3D images of this material called "Zwischgold."

 

The pictures reveal this was a highly sophisticated medieval production approach and revealed the reason restoring such precious gilded artifacts is quite hard. 

The samples studied at the Swiss Light Source SLS using one of the most advanced microscopy approaches were extraordinary, even for the highly experienced PSI team. 

Small samples of materials taken from wooden statues and alter originate from the 15th Century. Essentially, the altar is believed to have been made around 1420 in Southern Germany and stood for a long time in a mountain chapel on Alp Leiggern in the Swiss canton Valais.

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Materials Used in the Middle Ages

At present, it is on exhibit at the Swiss National Museum in Landesmuseum Zürich. The material sample was taken from two other medieval structures provided by Basel Historical Museum.

The material used in this study was published in the Nanoscale journal to gild the sacred figures. It is not gold leaf, although a special double-sided foil of silver and gold where the gold can be ultrathin because the silver base backs it.

According to PSI physicist Benjamin Watts, this Zwischgold was substantially cheaper than pure gold leaf. Even though the material was often used in the Middle Ages, very little was known about such material up to now.

Watts added that they, therefore, wanted to "investigate the samples using 3D technology," which can visualize ultra-fine details.

Zwischgold Investigated

Even though other microscopy approaches had been employed in the past to investigate Zwischgold, they only offered a 2D cross-section through the material.

This means it was only plausible to view the surface of the cut segment instead of looking inside the material. The scientists were worried, too, that cutting through it may have changed the sample's structure.

The 3D images bring a single drawback of using Zwishcold; nonetheless, the silver can push through with the gold layer to cover it.

The silver is moving surprisingly fast, even at room temperature. Within days, a thin silver coating is completely covering the gold. The silver comes into contact with water and sulfur in the air and corrodes at the surface.

Corrosion Enabled

Watts explained this made the gold surface of the Zwischgold turn black over time. He added the only thing one can do about this is to seal the surface with a varnish so the silver is not attacking the silver and forming silver sulfide.

The artisans that use Zwischgold were aware of the problem from the beginning, a related Nanowerk report specified. They use resin, glue, or other organic substances as a varnish.

Nonetheless, the researchers explained over centuries; this protective layer has decomposed, enabling corrosion to continue.

The corrosion also encourages more silver to migrate to the surface, producing a gap under the Zwischgold. 

Related information about nanoparticles and nanomaterials is shown on Minatec's YouTube video below:

 

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