Fresh from the Trench: Week 4

Light brown latch with a loop at one end and a very shallow hook resting in someone's cupped palms.

Right at the end of the day yesterday, one of our new students was working in the extended sondage near the trench entrance ramp. She found this iron object in the southwest corner of the mini-trench, abutting the edge of the cobbled yard in the southeast part of the trench. We think it looks like a latch, with a suspension loop at one end and a tapered, very shallow hook at the other end that might catch an “eye,” or loop/U-shape hammered into a surface. Even though it is corroded, it still retains the probable shape of the object rather well.

This isn’t always the case! Iron is particularly difficult to work with when it corrodes. Much of the iron we excavate are small objects completely covered in corrosion, sometimes identifiable as nails or tacks but other times just oblong lumps. On other sites, we have all seen iron concretions that reveal nothing of the original object until they are x-rayed! On another site, for example, something vaguely like a scotch egg appeared, and when x-rayed was shown to be multiple links of a chain that had rusted together. Iron corrosion is also very cheeky in that it often consumes or cements the iron object to nearby objects in the findspot, making them corrode as well. Think back to the image in our riddle solution post to see what iron and copper rivets look like corroded together: pretty unidentifiable at first glance. We have all seen iron corrosion pick up soil and sand, and sometimes even bits of bone and pottery!

How do we know it is iron? Many of the common metals we find archaeologically are fairly readily identifiable by their corrosion! Other clues like weight could be used but examining the corrosion allows you to simply observe particularly vulnerable metal objects without handling them. Iron commonly forms oxides, in an attempt to stabilize itself, and that’s how we end up with rust. Ferric oxide and ferrous oxide, brown and red/orange respectively, are what we find most often. Another metal that we have found on site frequently are copper alloys, which in our particular archaeological environment tend to turn green and pale green depending on the electrochemical changes; these colors represent the presence of chlorides rather than oxides. Lead, in addition to being much heavier than it looks, usually corrodes into carnbonates, giving it a white or grey appearance. Silver is most often affected by sulfur, leaving a black tarnish. And what about the shiniest-of-shinies? Gold doesn’t corrode hideously at all, it just becomes a purer form of itself!

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