Reconstruction of Manufacturing Processes

"Production processes of small pewter objects in the High and Late Middle Ages

The find of a thirteenth century complex of stone molds in Magdeburg increased our knowledge of the casting of pewter objects in the Middle Ages. Molds and casting waste can tell us more about the various production methods than the cast objects themselves. The same casting methods for pewter objects were used for centuries, namely full casting, core or hollow casting and the slush casting, i. e. the casting of three-dimensional objects by pouring out the metal that had not yet solidified (Vollgieß-, Kerngieß- and Sturzgießverfahren). The full casting method was most commonly used. In order to make a
successful cast the mold had to fulfill certain requirements. The mold was brushed with soot, lime water, or chalk slip. It also had to be heated so that the hot metal could flow freely to all parts and not solidify immediately. Another condition was the presence of vents by which air could escape from the mold and so prevent air bubbles forming in the cast. A great change in the thirteenth century was the enormous increase in pewter products. It was in this period that mass pilgrimage developed and the demand for cheap, quickly produced souvenirs grew. The opening of the tin mines in the Erzgebirge in the first half of the thirteenth century met this need. Tin was no longer a Cornish monopoly: it was a cheap alternative for gold and silver and became available to much more of the population. The lower costs led to a bigger market in west and north-western Europe, to the development of pewter/tin molding as an independent craft and the emergence of the tin molders gilds in Paris (1268) and Nuremberg (1285)."

Geometrical, ornamental and pictorial decorations are to be
found on a variety of metal objects of the Early Bronze Age
north of the Alps. They were applied to the objects by means
of various techniques, mostly to enhance their visual appearance.
Besides frequently used decorating techniques, there
are also those which are considered exotic in the metallurgical
industries of the middle, west and north-European Bronze
Age as they are only represented by few finds or their actual
use of the technique is even open to question. Amongst these
are the decorating techniques of damascening, patination
and arsenation; the last two named processes were used to
change the colour of the surface.
Starting with the Nebra hoard and further Early Bronze
Age objects, these techniques have been investigated by experimental
and archaeo-metallurgical research. The aim is to
reconstruct their application and artistic use. Especially
important knowledge has been gained about the technique of
damascening. The technical possibilities for the application
of Bronze Age patination can be gained experimentally, but
they cannot be necessarily proved on objects themselves. The
same applies to arsenation. On the other hand it becomes
clear that many linear decoration schemes on Bronze Age
objects are created by chasing and not through casting or
engraving.

The use of artificial patination techniques in antiquity for deliberately changing the colours of metals through the production of corrosion layers on the surface, has been strongly discussed for many decades. However, until now there is only evidence for such practices from ancient Egypt, the Mycenaeans and the Roman period. The present paper therefore shows for the first time that thermal treatment was intentionally used for artificial patination in Late Bronze Age Europe. This is illustrated on a supposed Italian winged axe using a combination of scientific techniques. The analysis shows the aesthetical intention of the craftspeople, as it can be clearly demonstrated that a strong colour contrast was favoured. The object is therefore not only the earliest example illustrating this kind of patination technique but also testifies the selective use of metallurgical knowledge on the cusp of the Early Iron Age. It further opens the possibility that colour treatment of European metal artefacts was more common in non-classical antiquity than has previously been thought.

Gold parting enabled the production of very pure gold for various purposes from the sixth century BC onwards, but analytical proof of this pyrotechnical process is difficult. We describe a new analytical approach for the identification of purified gold combining silver and copper isotopic with trace element analyses. Parting experiments were performed with gold-silver-copper alloys using the classical salt cementation process to investigate potential silver and copper isotope fractionation and changes in trace element concentrations. In addition, we provide the first comprehensive dataset of silver isotope ratios of archaeological gold objects from the Mediterranean and Central Europe to test whether or not gold refining can be identified on the basis of isotope systematics. The results show that very heavy silver and copper isotopic compositions are clear evidence for parted gold, but that the application of copper isotopes might be limited.

Gold parting enabled the production of very pure gold for various purposes from the sixth century BC onwards, but analytical proof of this pyrotechnical process is difficult. We describe a new analytical approach for the identification of purified gold combining silver and copper isotopic with trace element analyses. Parting experiments were performed with gold-silver-copper alloys using the classical salt cementation process to investigate potential silver and copper isotope fractionation and changes in trace element concentrations. In addition, we provide the first comprehensive dataset of silver isotope ratios of archaeological gold objects from the Mediterranean and Central Europe to test whether or not gold refining can be identified on the basis of isotope systematics. The results show that very heavy silver and copper isotopic compositions are clear evidence for parted gold, but that the application of copper isotopes might be limited.