The design of the original reconstruction of the Cairns Pin is the result of 3 months of intensive work for Ben Price’s MSc dissertation while attending the University of the Highlands and Islands Archaeology Institute.
The Cairns Broch
The Cairns is an Iron Age broch site situated near Windwick, South Ronaldsay, Orkney. The excavations, led by Martin Carruthers, have been ongoing each summer at the site since 2006. To date they have discovered an Iron Age broch that has been filled in after it has gone out of use but further Iron Age settlement of the site has continued into the 8th Century AD. This later use included a smithy and associated workshops tentatively dated to the 1st Century AD. It is within this area that an assemblage of over 60 mould fragments were recovered during the 2014 & 2015 season of excavation.
The Pin Creation
The dissertation aimed to answer the question:
“Can 3D scanning and model production be used to greater effect in artefact analysis?“
Utilising the Middle Iron Age non-ferrous metal working mould assemblage recovered from The Cairns broch. One of the aims was to explore to what extent our understanding of non-ferrous metalworking can be enhanced by utilising three dimensional scanning technology. In order to assess the impact of 3D scanning technology on the mould fragments, it was necessary to produce three dimensional scans of a selection of non-ferrous metal working moulds and use them in the analysis of non-ferrous metal working. Specifically, 3 fragments were singled out as being from the same mould of a ring headed pin and these were used in this study.
Various methods of scanning were looked at but in the end cost and availability meant that photogrammetry was used to scan the mould fragments. Photogrammetry is a method of using still images of an object or landscape to create a 3D model. It does this by identifying points on an image then tracking the changes in position over several images. If enough images are used covering all angles of the object or landscape, specialist software can do some incredibly complex maths to determine its position in 3D space.
For use with the moulds this meant taking a series of photographs at different heights and rotations around each fragment. To do this Ben used a modified “lazy susan” turntable, some black cloth and a digital SLR camera with a light ring mounted on a tripod.
In order to capture all the angles and sides of the fragments the turntable was turned about 40 degrees or so for each picture and was repeated for 3 angles over the fragment. The artefact was then turned over so that the bottom was captured. This wasn’t strictly speaking necessary for the virtual casting process but allowed a complete model to be created.
The image to the left shows the spread of images taken to create the 3D model. The blue squares represent each image and the software calculates the distance and position of each image to match them together and build a cluster of points that match all the photos. This is then used by the software to create the 3D mesh or virtual solid surface.
Once the photogrammetry software had created the model it was then imported into a 3D model editing program to conduct the “virtual casting”. This was done by removing the surfaces of the mould that wouldn’t have had contact with the liquid metal, then inverting that shape to give its cast form. While it would have been far simpler to use a piece of putty pressed into the mould, the virtual method has the distinct advantage of leaving the mould undisturbed, allowing for future residue analysis and with no risk of damaging the fragile detail.
Once all the shapes were “cut out” they were assembled together to form the pin. Reconstruction was required to fill in the blanks left by the missing fourth fragment. This was done using modelling software and comparing with similar pins at the Orkney Museum at the Tankerness House, Kirkwall. From the image below you can see the reconstructed part marked in red. The shaft of the pin was easier to recreate and was done so by simply mirroring the lower half, here marked in green.
Once this was done the model was prepared for 3D printing and sent off to Shapeways to be 3D printed in wax and then cast.
And what of our original goal of assessing to what extent our understanding of non-ferrous metalworking can be enhanced by the use of 3D scanning technology? While the 3D scanning, model manipulation and physical production of the moulds and associated objects has undoubtedly stirred much thought, it is not a direct answer to this question. Certainly physical production of the pin has provided a very clear answer as to what the missing resultant object would likely have looked like, and even without a 3D print of the object, the 3D model would have provided nearly as much of this insight. The 3D models of the moulds themselves also allows the possibility of further work in the reconstruction of the moulds themselves, or to suggest new shapes for the missing pieces.
If you have acquired one of the pins you are probably already aware that actually holding the object allows you to imagine both the practical use of these objects and perhaps something of their social importance during the Iron Age. This was a surprising and unexpected side effect of this study and is an aspect that should be explored further.
Ortak and the Pin Range
During the Christmas period of 2016, the bronze pin was put on sale for a limited time to see if there was interest in the pin as a product in association with the Orkney Archaeology Society. The response was very positive and it was decided that a larger approach would be beneficial for this item. We approached Ortak in the spring of 2017 and they developed what is now the Cairns Pin range from the original casting. I am very pleased that Ortak have taken this project on as they are an Orcadian company producing pins that their Iron Age ancestors once produced on these very same islands. These fantastic pieces are available in silver which is an archaeologically viable casting medium for this kind of artefact. The range includes the original reconstruction as well as more refined forms including wearable items such as necklaces, earrings and brooches.
You might also be interested in bronze copies of the pin model both in un-finished and finished forms. These use a more detailed 3D model and are not available anywhere else. For more info see this post.
More information on The Cairns including an daily excavation diary for the site can be found here : http://www.orkneyjar.com/archaeology/thecairns/
An unpublished academic paper on the construction process for the pin can be obtained here : Virtual Coppersmiths – Exploring Iron Age non-ferrous metalworking utilising 3D scanning and printing