Tin

Currently it is believed that Kish, at around 2700 B.C., provides us with the earliest instances of the alloying of tin with copper to make bronze in ancient Mesopotamia. 

ED I: 
Range: <0.012%–5.8% (n=13) 
Highest Sn-level: Flat adze (inv. FM158 183)

ED III/Akk: 
Range: <0.014%–9.7% (n=43) 
Highest Sn-level: Pin, lapis-headed (inv. FM228 515)

Among tools and weapons, there is little or no evidence that tin was being added deliberately to achieve any functional gain. For example, among the four adzes from the EDI phase, the Sn-content varies from <0.012% to 5.8%; and among the five daggers from the EDIII/Akk phase, the Sn-content is always <0.11%. To create a tool or a weapon with any significant toughness would require an Sn-content of about 4% (Northover 1989).

Equally, among Kish’s numerous decorative pins (toggle or plain), there is little or no evidence that tin was being added deliberately for any aesthetic purpose. Only an Sn-content of about 12% or more would give bronze a golden hue when freshly cast (Chase 1983); yet only one item, the lapis-headed toggle pin (inv. FM228 515), has an Sn-content >6%. 

The absence of bronzes with an Sn-content that lies between about 0.5% and 1.7% suggests that the latter level is a marker for the deliberate addition of tin for whatever purpose. But even trace levels of tin in copper ores is rare, so the numerous instances among Kish bronzes—i.e., 20 of the 56 artifacts studied; thus, 36%—that have a Sn-content in the range of 0.1% to 0.5% might suggest that recycling of scrap bronze, and some mixing of that bronze with basic copper stock, was quite common. A similar situation does not seem to hold true for bronzes from Ur, where only 13 of the 87 artifacts studied—thus, 15%—have an Sn content in that range (see Ur).