Tagging visible pots

Wednesday 24.8.2016

Today our task was to tag all visible unmarked bow area pots, that had lost their tag for some reason. Stella and her team of archaeologists has identified 18 such pots. First we had to make new tags for them and plan for the dive. We had the bow area plan with all amphorae drawn on tracing paper, which was taped to a slate.

The bow trench team prepares the slate and makes finds-tags to be attached to the amphorae. Each tag has a unique number (e.g., P0154, where P stands for "pot" type of a find). These amphorae had been tagged earlier, and it was important to tag them again with the same number. It would have been so easy (and fast!) just to place some tags for all those untagged amphorae, document it, and then map each new number to given old number. You would imagine that an archaology finds management software would easily handle such cases. You would be wrong.

The idea was for diver A to handle all tags, and give them one-by-one to diver B in predefined order. Tags were attached to a string to keep the order correct.  Diver B would then use then given plan on the slate to locate that amphora, and attach the tag to it with wire. Best place for the tag would be one of the handles (amphorae have always two handles), then the neck, and finally the narrow amphora toe. Diver A would then give diver B the next tag, and, while diver B was looking for that amphora, diver A was documenting the previously tagged amphora with GoPro. Etc.

This all sounds easy, simple and straightforward, but it is far from it in 43m depth with some nitrogen narcosis. On top of that the first pair found wreck site in real bad visibility, only some 2-3 meters. Locating correct amphorae ("if you are not absolutely sure, do not attach that tag!") turned out very difficult and they got only 4 amphorae marked. They were actually worried about finding the ascent line in time. So, the first pair brought back 14 tags to the the second pair. We had better visibility, and located and tagged five amphorae in just 6 minutes. Then things got confusing because the map was not perfect and the first team had made some misleading notes there. Or maybe it was just our nitrogen narcosis that prevented clear thinking, because the notes had looked just fine on the surface. Either way, we tagged only those 5 amphorae, and then rummaged around the dig helplessly chasing our own tail... until mercifully the 20 minutes bell rang.

So, we tagged altogether only 9 amphorae out of 18. We will probably continue from that tomorrow, and hopefully then start practicing with the airlift. Overall plans on the dig change quite often based on circumstances and what each team has achieved/found so far. It is not clear if we have to locate and tag all remaining 9 amphorae in the bow, before we start lifting amphorae to surface. However, only properly marked amphorae will be raised.

In the evening we had very interesting lecture on photogrammetry. We also got to practice it a little bit with given photographs and control point data set. Photogrammetry is a novel way to create 3D-models from given object (e.g., wreck site) just from multiple photos of that object. Each photo should have pretty much overlap will neighboring photos, and there must be a defined set on control points around the object. For good results, you also should have a good (i.e., expensive) camera and very accurate relative locations of those control points.With proper software that data can be processed to something called a point cloud, which in turn can be processed to a 3D-model or a large high definition photomosaic of that object. Or you can create a virtual reality model with proper texturing, so that it would also look like the real thing instead of just a wire model (e.g.). The model can be so accurate, that you can do all object measurements from that data, instead of loitering around a wreck (e.g.) with a tape measure. However, to get exact control point data, you might still have to do in situ measurements. So, an archaeologist carrying (or diving with) a tape measure is not quite passé yet. But almost.