Lead isotope ratios and the provenance of medieval silver

The material presented in this article is certainly interesting and the authors present data and interpretations concerning the technology that was used to produce silver jewellery in the Middle Ages in western Poland, with an emphasis on the granulation technique and on the provenance of the silver. They claim to have identified three different joining techniques, namely "(i) spilled granulation ornaments, (ii) non-oxidised spherical granules and (iii) oxidised soldering area with spherical granules". From the images provided, it seems that the first technique relates to soldering with metallic solder and the second to reaction soldering with copper salts. But it is unclear what the authors mean with "the use of non-metallic soldering". In the discussion on the soldering techniques, they refer to the measured oxygen contents but do not discuss the possible influence of corrosion. It is also not made sufficiently clear why linear discrimination analysis had to be used to determine the compositional difference of the base metal and the soldering regions.