(ORDO NEWS) — The researchers used 3D imaging to study a nanomaterial called Zwischgold. This is how it might have been used in medieval art.
Zwischgold (Tsvishgold, “partial gold”) is an ultra-thin metal foil, consisting of a gold top layer and a silver base, used for gilding sculptures.
Until now, the researchers have only studied 2D sections of this material, but in the new work they have gone further and for the first time were able to create 3D images of Zwischgold, and find out how it was created and why historians may face problems in restoring medieval art.
Nanotechnology of the Middle Ages
Among the four 15th-century specimens examined was one from an altarpiece originally located in a mountain chapel on Mount Leigern in Valais, Switzerland, now on display at the Swiss National Museum (Landesmuseum Zürich).
Although Zwishold was often used in the Middle Ages, very little was known about this material until now. Therefore, the scientists wanted to examine samples of this nanomaterial using high-definition 3D imaging technology.
To do this, the researchers used a sophisticated microscopic imaging technique called ptychographic tomography, in which X-rays pass through a sample of material to create shadows of varying intensity, called diffraction patterns.
By improving imaging techniques and combining different diffraction patterns, details as small as millionths of a millimeter can be revealed. The researchers describe it as a “giant Sudoku puzzle” where with each additional image, the whole picture of the object is gradually revealed.
The scan shows a layer of gold about 30 nanometers in size, thinly and evenly spread over a layer of silver base (some of the thinnest human hair is about 50,000 nanometers long). By comparison, analysis of modern Zwischgold specimens by the same study showed thicknesses ranging from 48 to 82 nanometers.
A sheet of pure gold produced in the Middle Ages without silver would have measured around 140 nanometers, so Zwisgold was cheaper to produce due to the lower amount of gold needed.
It may also have been difficult to create, potentially requiring special tools and skill. The researchers speculate that the gold and silver were bonded together before being processed into a single foil.
Fortunately for sculptors and gilders, gold and silver retain a uniform morphology when their crystals are pressed together. However, the restoration of medieval art will now have to take into account the structure of Zwisgold and try to recreate the same material in modern conditions.
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