He [Birka] states that metallic solders were introduced into
Mesopotamia during the 3rd millenium BC. (he cites Wolters, J.,
1983 "Die Granulation. Geschichte und Technik einer alten
Goldschmiedeknust. Munchen.) Not sure if anyone has access to the
cited publication (and can read German) but I'd be curious to read
In English, the very best book to buy/get from an academic
library/get on Interlibrary Loan is P.R. S. Moorey's Ancient
Mesopotamian Materials and Industries--The Archaeological Evidence
(published in 1994 by Clarendon Press, Oxford, and re-issued by
Eisenbrauns, Winona Lake, IN.) On pp. 229-231 and p. 274, Moorey
discusses ancient soldering, and references to several articles on
ancient joining (many in English) are given.
Moorey's book is a classic and will not soon be superceded. Besides
precious and base metals, he also discusses ancient working with
stone, bone, ceramic, glass, and wood.
There is (to my knowledge) no Mesopotamian art work depicting
metalworking processes. If you like pictures, see the booklet,
Egyptian Metalworking and Tools, by Bernd Scheel (1989; Shire
Egyptology -- I think I bought it at the British Museum in London).
Scheel mentions that the Egyptians used hard-soldering, but that
they were preceded in this by the Sumerians.
As has been mentioned before, Jack Ogden's books on ancient jewelry
(jewellery) are also informative.
Happy reading! -- Judy Bjorkman