Hard soldering—the joining of two pieces of gold alloy at a temperature around 800 degrees by means of adding an alloy of different ratios—is known occasionally in the ancient world: 4th millennium BC Mesopotamia and central Iran, 3rd millennium BC Indus Valley, and New Kingdom Egypt where it was used for ring shanks (Stone forthcoming). However, it was not common, probably for several reasons. When alloy ratios are different from solder ratios, a flux is needed, but natron provides an imperfect bond and there is no reliable evidence of borax until the Middle Ages (loc. cit.). A fine-tipped blow pipe and the equivalent of iron binding wire would have also been useful for hard-soldering in ancient times, but there is no extant evidence for them. It is thus assumed that the instances of hard-soldering that have been noted took place by putting the relevant object into the fire or using the flame of a large blow pipe. These methods would not have been suitable for fine work.
Fig. 224. Ancient and modern joins compared through SEM. Above left, dropshaped element from Cat. 130 with a diffusion join between ring and bowl. Left, modern drop-shaped element from Cat. 298 showing crimped wall, massive solder around ring, and file trenches on its top surface
Fig. 225. Ancient and modern inscriptions compared. Left, chased inscription on ornament MMA 26.8.130, Cat. 141. Right, engraved inscription on modern tall-necked jar. Cat. 263
A. Wady Qirud-type rosettes with thin backs, loose coupons, stamped buttons, V-shaped spokes, and a few ancient rosettes mixed in. Cat. 277
B. Back side of rosettes with round petals and hieroglyphs. Cat. 284. i:i
C. Back side of rosettes with round petals and hieroglyphs. Cat. 283. i:i
D. Back side of rosettes with straight spokes and hieroglyphs. Cat. 288. i:i
In the hard solders of objects below that are believed modern (Appendix 2, third section), the copper percentage is often considerably greater in the solder than in the base alloy (244, 254, 261, 300, 313). This is not always the case, however, see analyses there for 235, 307, 308, 315. Also to note, the bead type known from Cairo bazaars (last entry in Appendix 2) has similar levels of copper, silver, and gold in base alloy and solder, but 2.1 cadmium is present. In the case of the acacia-bead spacers 313 and agate buckle 315 believed modern, the higher amount of copper in the solder was considered with negative technical and formal arguments.
Parenthetically, soft soldering is done at a low temperature (around 200-300 degrees), usually with a tin-lead alloy. Stone does not know soft soldering in antiquity for gold work; he knows it for bronze, and has seen it on Roman silver, but not in pre-Ptolemaic Egypt.
As for working with hard solder in modem times, as stated above, a poor goldsmith will often remove excess solder by filing. A drop element below, believed modern, shows not only hard solder but filing channels (Fig. 224 [top]; cf. a drop element with a diffusion join in Fig. 224 [bottom]). Further, Baines states that if the temperature is not regulated carefully, the flux (possibly natron) can burn out and oxidize the solder, which is then unable to flow. If this happens, the surface sweats (becomes blistery, or creased, like boiled milk), and if further heat is applied, the copper, zinc, or tin of the alloy can bum out. Then, if additional solder coupons are applied, and their surfaces oxidize also, they won’t flow either. These conditions are thought to explain the appearance of many rosettes considered modern (Fig. 226a). While some ancient east Mediterranean work shows overheating (cf. Lilyquist 1993b: 49), it is to a much less degree than on objects here.
World History
