It took me awhile to find it, but the reference to the use of amber
for granulation is real: Thelma Follett, "Amber in Goldworking, "
Archaeology 38 (1985): 64-65.
For a good discussion of ancient amber, see P. R. S. Moorey, Ancient
Mesopotamian Materials and Industries (Oxford 1994): 79-81. Moorey
says (ibid.: 79), "It seems that amber was used by the Etruscans as a
flux in colloidal soldering of goldwork; a search for eastern
parallels or precursors has yet to be undertaken (Follett 1985)."
Moorey also has a good discussion of possible examples of ancient
Mesopotamian granulation on pp. 230-232 of his work.
Examples of Mesopotamian granulation dating to the early second
millennium B.C. are discussed by Rachel Maxwell-Hyslop, “The Pair of
Gold Earrings from Ur, Grave 114, and Remarks on the Technique of
Granulation,” in the book, Collectanea Orientalia (Festschrift for
Agnes Spycket) (Paris; CPOA 3; 1996), p. 205 ff.