florins and ducats, in the same manner as contemporary gold leaf. 8,9 The materials for producing Zwischgold were supposed to be fine gold and fine silver 12 and it is assumed that the gold was sourced from high quality gold coins, e.g. 8–11 The production of Zwischgold is recorded to involve adhering a thin gold layer over a thicker silver base with a so-called “cold welding” technique. part-gold in English, 4 or parti in French, 5,6 and oro di metá in Itatian, 7 but is now commonly referred to by the German word Zwischgold. 2,3 This new laminated metal leaf has been known by many names in different languages, e.g. 1 The technical innovation of gilding, where thin leaves of gold are used to cover a surface, greatly reduced the cost of producing large “golden” artworks and significantly expanded the decorative use of gold.Ī further innovation appeared in medieval Europe, whereby the gold leaf was backed by a relatively thicker, cheaper metal (usually silver) so that the expensive gold layer could be made thinner than contemporary gold leaf and hence reduced the gilding costs by at least half. In the medieval material hierarchy, gold possesses the ultimate position, reflecting the splendour of God and representing the brilliance of divine wisdom, or simply the Holy Scripture.

Throughout the history of human civilization, lustrous gold has been a favoured material for displaying wealth, prestige and power. As supportive data, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray analysis (EDX) were performed on the medieval samples. Further, a rare variant of Zwischgold that contains extremely thin multiple gold layers and an overlapping phenomenon of Zwischgold with other metal leaves are observed through PXCT. Each of these effects speak to typically observed issues in the conservation of such Zwischgold applied artefacts. The measurements clearly demonstrate decreasing density (increasing porosity) of the leaf materials and their corrosion products, as well as delamination of the leaves from their substrate. We have acquired quantitative, 3D nanoscale images of Zwischgold samples from 15 th century artefacts and modern materials using ptychographic X-ray computed tomography (PXCT), a recently developed coherent diffractive imaging technique, to investigate the leaf structure and chemical state of Zwischgold.

The conservation of such Zwischgold applied artefacts has been an obstinate problem. Zwischgold corrodes quickly when exposed to air, causing the surface of the artefact to darken and lose gloss.

Many European sculptures and altarpieces from the Middle Ages were decorated with Zwischgold, a bilayer metal leaf with an ultra-thin gold face backed by silver.

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