Dig Diary – Wednesday, July 12, 2017
Back to the Iron Age and another carinated sherd?
Today began with a site tour for diggers to bring them up to date on what we have done, what we will do and the latest thinking on this most complex of sites.
As they lined the trench sides to hear the various supervisors describe their charges, it became more obvious than ever that there are a significant number of diggers working on site.
So far there are perhaps 60-70, and some of those will leave at the end of this week. But more are due to arrive, bringing numbers up to around 80.
A good proportion of those will be retained in Trench T, where the number of Neolithic pits excavated has now reached 50.
Supervisor Dave has moved a number of diggers back up the trench to the area of the Iron Age stone “collar” which forms the top fill of a revetted ditch. He will open a section across the ditch, which may turn out to be substantially deeper than it appears at the moment.
This would be good, for a nice deep ditch should reveal information about the Neolithic levels which lie below and through which it was cut.
One of the most interesting aspects of Trench T this year is the interest shown by the public, who are allowed to visit for the first time as part of a tour.
The elements in the trench are at an early stage of excavation but the enigmatic, not to say mysterious, nature of what is being revealed has clearly captured the imagination of those on guided tours who listen with rapt attention.
One of the fascinated visitors today was Professor Colin Richards, Britain’s pre-eminent archaeologist and a regular visitor to the Ness.
His accumulated experience is immense but it was nice to see that even he could be startled by the possibilities surrounding the Neolithic structures at the bottom of the trench.
Site director Nick is more persuaded than ever that there are similarities between the Trench T structure and the Bookan chambered cairn, a mile or so away, which he excavated in 2002.
He believes that orthostats in Trench T may have been used in a similar way to that revealed at Bookan, although the Bookan structure is much smaller that Structure Twenty-Seven in Trench T.
In Structure One, the curving secondary wall is being removed with each stone being washed and examined from every angle for signs of decoration, and in Structures Eight and Twelve an energetic programme of floor sampling is being undertaken. Our decorated stone expert, Dr Antonia Thomas, is on hand to give advice.
Specifically in Structure Eight (with its six hearths) a depth of material has accumulated around the hearths with, paradoxically, no clay flooring in the side recesses.
This may indicate the original presence of platforms in these recesses.
In Structure Twelve, the two major hearths are being sectioned and the sampling work will be supplemented by the imminent arrival of our archaeomagnetist, Sam Harris, together with his PhD supervisor from the University of Bradford, Dr Cathy Batt.
Sam’s work is already looking very promising in the task of adding archaeomagnetic dates for the Neolithic, where such dates are scarce.
Structure Ten still looks empty because the glaring sun strikes it as such an angle that supervisor Sarah finds it virtually impossible to discern the subtle changes in her floor deposits.
Short of conducting a rain dance, she has been unsure what to do, but help is now at hand in the form of Jim , the man who can solve any on-site problem.
He now proposes to build a shelter for Sarah, a sort of polytunnel, with wood donated by Buildbase, in Kirkwall, and polypropylene piping from Ness stalwart and long-term supporter, Denise.
There may be a hidden benefit in all this for Sarah who is, shall we say, petite. If we apply water to her roots (sorry, boots) when she is in the tunnel, she might grow.
Lastly, and for the hordes of salivating pottery fans out there (all three of you) a deep excavation of part of the floor of Structure Fourteen has produced what looks like another sherd of carinated bowl.
This would match the carinated sherd from a nearby sondage, whose date of circa 3500BC was confirmed by dating of associated material, and by Hugo’s identification of an early flint from an associated context.
This is exciting, if expected, for, as the title of our new guidebooks states, we are “digging deeper” – see http://www.nessofbrodgar.co.uk/product/guidebook/.
Working on the wall – Jim Bright
One of the advantages of being on an archaeological site during its excavation season is the ability to make 3D models of structures at different phases of excavation.
During the course of excavation at the Ness of Brodgar, I will be recording the excavation of the curving, northern wall in Structure One, creating 3D models of the wall as it is removed.
Sketch plan drawings are created during the course of the removal of a structure such as this, usually after every layer or phase of the structure had been removed, however creating a 3D model of the structure at these intervals can add an extra level of detail for the archaeological record.
Indeed, one can view the wall as it was at a certain period of excavation and compare this with the plans which are normally sketched, to aid in interpretation.
There are potential problems which need to be avoided when creating a model of a structure such as this.
The first issue is the sun. One could be under the impression that creating the 3D model in sunshine would add an extra, brighter level of detail, however there are issues with this. Shadows can be problematic during any photographic work when recording archaeology, as they can hide details which would be visible in a more over-cast environment.
Moreover, they can give an inaccurate perspective of a structure or trench when photographed at certain angles. This is often an unavoidable problem when recording on an excavation. However, this is only one issue caused by shadows when creating 3D models.
Shadows can also potentially confuse the 3D modelling software when taking multiple images. If the sun is hiding behind clouds when I start the photogrammetry process, and then comes out halfway through, I have a model where half the model has shadows and the other half is overcast. The modelling software may then have trouble identifying the area as one structure and model.
Another issue can be the rain – if it had been raining and there are small puddles in the area to be modelled, the reflective surface of the water can also cause problems for the software. These issues can be overcome by either removing the puddles with sponges or removed from the model digitally, however this is far from ideal.
Finally, if it is very windy and there are objects in the structure that are moving about, the software will again be confused by the movement and won’t be able to align the photographs in order to create a point cloud, or at the least will create a blurry, poor quality model.
I’ll describe this process of point cloud creation in more detail in another blog, but as far as the process of taking all the photographs is concerned, all these issues are best avoided if possible.
The perfect “Goldilocks” conditions for a nice 3D model of a structure such as the wall, are overcast, when it hasn’t been recently raining and it is not too windy, conditions that are can be often hard to capture when working in Orkney, so there are always new skills to be learned in order to work around these issues.