Dave Johnston, from the Warship Hazardous Project Group describes how a national scheme for providing free access to state-of-the-art University X-ray computed tomography (CT) facilities allowed the group to examine ordnance from a 1706 shipwreck. 

Warship Hazardous Prize is a protected wreck that lies in the shallows of Bracklesham Bay, West Sussex. The ship was deliberated ran aground in late 1706 to save lives after her anchors failed in St Helen’s Roads in horrendous south westerly gales at the end of a disastrous voyage from the Virginia colonies as escort to a large merchant convoy. The ship soon broke up and was lost beneath the waves, until rediscovered by members of 308 branch, Sub Aqua Association in 1977. The site was protected under the Protection of Wrecks Act (1973) in 1986.

In the all too brief autumnal gap between COVID-19 lockdowns that defined the 2020 UK diving season, a small team from the Warship Hazardous Project Group www.hazardousproject.info was able to muster and dive to assess site changes. The previous year we had discovered a second extension to the main wreck site in the form of a scatter of 10 large cannon, bar and round shot, a “small” anchor and other artefacts. This site lay some 100m away from the hull remains and 60m from another scatter of 11 large guns found in 2014. Much of the 2019 site had already been reburied by the ever shifting sands but an area some 20m to the south west had been exposed, revealing 2 large copper cooking pots stacked one inside the other, a cast iron, tripod-footed pot and other artefacts including numerous bar shot, sounding leads and a heavily concreated linear item some 1m long with small bulges at one end, which we suspected could be the remains of a musket.

  

Above: Photogrammetric Digital Elevation Model of the 2020 extension to the 2019 gun site courtesy of Dan Pascoe and Rodrigo Ortiz.

 

One thing noticed by the dive team was that the bar shot all seemed to be asymmetric with one end significantly larger than the other, which we found rather strange. The decision was taken to raise the putative musket and some of the barshot for further investigation. 

Above: The “musket” and 2 asymmetric bar shot after recovery. Image: author.

 

At this stage, we were fortunate enough to be able to blag access to a conventional X-ray machine that Bournemouth University was evaluating and were able to X-ray the putative musket and confirm that it was, indeed, a flintlock musket.

 

Above: Conventional X ray imaging confirmed a concreted flintlock musket in seemingly good condition. Images: Dan Pascoe.

 

Moreover, it appeared to be in remarkable condition considering that it had spent over 300 years on the seabed – a flint was still clamped in the hammer!

As anyone who has attended a NAS conservation course will know, the worst kinds of artefacts to conserve are those of composite construction as the different materials often require different and incompatible treatments, so this was clearly going to be a real challenge to whoever we asked to undertake conservation, not least in de-concreating it without damaging the exposed parts of the lock mechanism. Clearly we needed to get as much information as possible from it before handing it over to guide the de-concreation and conservation process.

The concreated bar shot were, however, well beyond the penetrating power of that X-ray system. De-concretion of some of the recovered bar shot revealed that the 2 ends of the surviving ironwork were indeed different shapes and sizes, not something that had been recorded from historical records. Close examination suggested that this could be an artefact of differential corrosion / survival of the 2 bar ends resulting from composite construction, one end being cast into, or hammered from the original bar, the other added from a separate piece of metal. To further investigate this, imaging of the interior of still concreated specimens would be of value – even if the encased shot was badly corroded, there would potentially be a void space where the corroded material once was which could reveal its original shape and size.

Both the musket and the concreated bar shot clearly called for access to high power X-ray imaging facilities and ideally to computed tomography X-ray imaging (CT) where the sample is rotated within the X ray beam to collect a set of images from different angles which are then assembled by computer to generate a 3D data set.

Therein lies a significant problem for a volunteer group, the type of specialised equipment needed for CT of large lumps of metal is often locked away in university engineering departments with access charges of around £1000 a day, and we were going to need several day’s worth of beam time to record the musket and the bar shot.

Then we found out about the National X-ray Facility NXRF (https://nxct.ac.uk/). This is a “virtual facility” comprising the X-ray and CT-facilities of various English universities (Manchester, Southampton, Warwick, University College London) and the Diamond Light Source at Harwell. These facilities receive core funding from the UK Engineering and Physical Sciences Research Council to provide facility access and expert support for academic and industrial users who need to run cutting-edge, 3D imaging experiments. Crucially, this core funding also allows them to offer an amount of free beam time and expert support to first time CT users from academia and not-for-profit organisations! Applications are made to the central NXRF administration team on a simple and brief form describing what the end user wants to image (including size, weight and any handling requirements (our samples needed to not dry out), what the data was needed for / what it was hoped to reveal and how the data would be used and disseminated (https://nxct.ac.uk/wp-content/uploads/2021/05/NXCT-Free-Beamtime-Access-Scheme-Eligibility-guidance-May-2021.pdf).

Applications to NXCT are assessed for feasibility and, if accepted, users are assigned to the partner organisation with the most appropriate equipment. What did we have to lose? An application was submitted and accepted and we were assigned to Southampton University’s MuVIS facility for access to its Hutch CT system (https://www.southampton.ac.uk/muvis/about/equipment/hutch.page), a custom built, high powered microCT system capable of imaging samples up to 1m x 1m x1.5m and 100Kg.

COVID-secure delivery of the samples was arranged for the next available free slot on the system (some 3 months later, it is in very high demand) which gave us time to design and build a large, sealed Perspex tube to firmly support the musket upright in a humidified atmosphere (it was still undergoing desalination). We had been assigned 3 days of beam time to image the entire musket at high resolution (<0.25mm voxel size) and to scan 2 concreated and 2 de-concreated barshot at lower resolution. In the end they gave us 4 whole days and asked to borrow the bar shot for longer for their own method development to test out how they imaged on other systems.

Initial inspection of the musket data set reveals how remarkably preserved it is:

• the flint is still wrapped and clamped in the hammer, and the screw thread on the flint clamp is visible
• the frizzen and flash pan are still present and the flash hole is visible,
• the barrel is shaped from octagonal at the butt end to circular at the open end
• the ram rod is still slotted into the underside
• the closed end of the barrel is sealed with a threaded plug
• all the internal springs and locks are still present
• the growth rings of the stock timber are visible in the butt
• the shape of the recess in the stock that holds the flintlock mechanism is clearly visible.

These data will be crucial guides to help the conservator deconcrete the item. 

 

Above: 3D volumetric view of the musket (image: author)

Above: Hammer with clamped flint, frizzen with spring and flash pan (image: author)

 

Above: Flintlock internal mechanism (image: author)

 

Above: Threaded butt seal (image: author)

 

Above left to right: growth rings in butt timber; barrel, pinned stock and ramrod; octagonal barrel at lock mechanism; 

flint clamped into hammer and screw securing the trigger guard (images: author) 

Above: CT animation of the ramrod spring clip

Getting to this point has been really simple; £4,000 of state-of-the-art, high resolution 3D X-Ray imaging for free for a short and painless application! We strongly advise other UK volunteer groups to try for free, proof of concept access where recovered artefacts would benefit from CT analysis.

Now for the hard bit, which we volunteered to do ourselves; segmenting all of the detail in the images from the background to produce full 3D models of the different components (there are about 1400 slices in the musket data so this will take considerable time and effort!). We are fortunate to have access to the necessary high end computing resources and software needed for this, but other groups can include analysis in their support request.

As for the barshot, that’s another story for another day, hopefully coming to IJNA soon.

We wish to thank Drs. Katy Rankin and Sebastian Rosini and colleagues at the Southampton MuVIS facility for their enthusiastic help and support for our project, and the NXRF for the funding support which allowed it to happen.

For a recent update of work on the Hazardous site, check out our article in the 2020 issue of Historic England’s Research News (https://historicengland.org.uk/images-books/publications/historic-england-research-16/).