Gerhard Eggert
Electrochemist (PhD), since 1985 working in heritage science.
Chair, Objects' Conservation, 1998-2019, Stuttgart State Academy of Art and Design
Chair, Objects' Conservation, 1998-2019, Stuttgart State Academy of Art and Design
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Papers by Gerhard Eggert
on the results of Oddy tests for corrosivity was examined.
Solvents can distort Oddy test results, leading to
false-positive or false-negative outcomes. Acetates such
as ethyl acetate and n-butyl acetate can cause corrosion
by hydrolysis into acetic acid and alcohol. A comparison
of the drying methods showed that heat drying at 60°C
for 14 days is suitable for most acrylic solutions. However,
particularly for slow-drying solutions, longer drying times
may be required. The results suggest that the use of acetates
as solvents should be avoided in conservation.
From at least the 15th century through the 19th century, “gilding waxes” were used as agents to manipulate the colour of fire gilding. These were mixtures of beeswax, usually containing red ochre, copper compounds and other ingredients. After the evaporation of excess mercury, fire gilding could be covered with gilding wax and reheated in order to achieve a colour shift from pale greenish yellow to a reddish appearance. Approximately 80 written sources – originating in seven different languages – from the 14th through the 21st century were studied, revealing approximately 300 recipes as well as information regarding production, use, alleged effect, etc. of gilding waxes. The earliest references to the technique, including brief recipes, come from the southern German-language region in the 15th century. owever, an even earlier origin is to be assumed. Through the second half of the 18th century, gilding waxes became part of mise en couleur practice in France. Further indication for the widespread and well-established application of gilding wax includes, for example, references to the practice in goldsmiths’ ordinances and the existence of ready-made products offered by pharmacies. The source research provided a foundation for a series of experiments and subsequent analyses, resulting in a broader understanding of the application of this technique and the physico-chemical effects of gilding wax treatments on gilt surfaces. This findings have implications for the conservation and further technical study of historic fire gilded objects.