A Comprehensive Study of the Sigebert of Frankenburg Seal from the Collections of Nicolai Likhachev

Abstract

The work presents the results of a complex study of a unique specimen of Western European sphragistics: the seal of Count Sigebert of Frankenburg (Holy Roman Empire, 12th century). This specimen stands out from the general masses with its distinctive dark burgundy color. Furthermore, it belongs to the period when the practice of coloring wax seals originated and the technology was in its formative stages. A comprehensive approach is applied to identify the materials used to make this piece, which included several methods: optical microscopy, polarization microscopy, Fourier-transform infrared spectroscopy, X-ray fluorescence analysis, and X-ray structural analysis. It is found that the sample consists of pure beeswax, without any resin admixtures, which is already known from the 12th century. The coloring substance is natural bolus consisting of hematite and quartz. Such specimens are rare in Western European sphragistics and do not occur after the end of the 14th century. It is impossible to explain the refusal to use bolus by its rarity or complete inaccessibility, as the pigment is widespread. The reason is probably the dark, almost brown color, which was not beautiful enough from the point of view of medieval man, who appreciated bright pigments. The refusal to use bolus can also be explained by the fact that when bolus containing colorless SiO₂ is introduced, the wax mass becomes loose and friable. This leads to deterioration of the seal and loss of the image. In conservation practice, when planning the priority of work, such specimens should be inspected with special care and, if necessary, strengthened entirely.