Chalk Blocks from Perham Down and Larkhill

As part of the continuing development of RTI, and to build on knowledge of how to apply this technique on various sized objects and materials, it is important to compare, where possible, as many different types of surface marks as possible. In this case an opportunity arose to apply RTI to two chalk bocks recovered from two separate excavations, from a similar period but with two different surface treatments. The chalk blocks were obviously the same material with similar surface patina; they had been worked at approximately the same time but, one was carved with relief and one had applied pencil marks. 

Chalk Block from Perham Down

This chalk block or plaque was recovered from a section of WW1 front line practice trench at Perham Down on Salisbury Plain during an excavation commissioned by Defence Infrastructure Organisation. The object was cleaned and processed as normal and it became apparent that it was clearly carved with the words ‘Liverpool Reg’ and a difficult to interpret  design to one side. Part of the carved face of the plaque was abraded. The fragmentary nature of the block meant that the design was incomplete and required further research. It was common for Regiments to pass through the training areas, particularly the practice trenches and leave their mark, either individually or by regiment.
Initial research suggested that the plaque was carved by a battalion of the Liverpool Pals. In order to assist in confirming this information it was decided to see if RTI would reveal any further hidden surface detail which may aid in correct identification.
The first image (image 1) is viewed with the default setting. Here can clearly be seen ‘Liverpool Reg’ inscription along the bottom and the unusual carving, in a part square border, to the top right. When viewed in specular enhancement (image 2), the significant reflective qualities of chalk become apparent and highlight well the surface detail. What appear to be a set of diagonal cuts in the surface of the chalk at top centre, and at first thought to be damage, can also be seen to be deliberately incised into the chalk. When viewed in close-up and in default setting (image 3), a study of the style of the visible lettering ‘Liverpool reg’ revealed a ‘copper plate’ style specifically to the letter ‘g’ in ‘reg’. When the damaged area above ‘Liverpool’ was studied in close-up and in specular enhancement (image 4), the remains of a letter ‘g’, in a similar style to that in ‘reg’ can be seen. Other letters had been abraded away leaving only the letter ‘g’. Subsequent research into the regiments of Liverpool during the First World War identified The Kings Liverpool Regiment as likely candidates for the carving.
The Kings Liverpool Regiment was set up by Edward George Villiers Stanley the 17th Earl of Derby in response to Lord Kitchener’s appeal for 100,000 volunteers in August 1914. Within five days, the total of volunteers had reached 3000 and by October, there was enough from the city to form four Pals Battalions in the Kings Liverpool Regiment. Lord Derby was so highly thought of that King George V gave permission for the Pals to wear the Derby crest as their insignia. Lord Derby produced silver cap badges for each of the men. The crest depicts an eagle carrying or guarding a child in a small boat above a crown. 
When viewed again under specular enhancement, image 2 reveals parts of Lord Derby’s crest. To the right of the image, and within the square border is the baby’s head lying in a crudely depicted boat. Directly above the baby’s head and just outside the top border is the end of a single talon of the eagle. To the top left of the image the curving angled beak of the eagle can be discerned.
In this instance, RTI was used successfully to analysis a delicate surface remotely causing no surface damage and also producing clearer evidence for the origins of the carving.

If you can't see the video it can be viewed on YouTube here

Chalk Block from Larkhill


The second block was recovered from WW1 practise trench systems at Larkhill, Salisbury Plain. This work is in advance of new Army housing and has revealed extensive trench systems and tunnels cut into the chalk. Soldiers passing through Larkhill for training before being sent to the western front have also left their mark.
A chalk block was recovered with names written in pencil. Due to the soft nature of the chalk and surface damage, some of the names were not clear. It was decided to try RTI in order to see if the graphite used in the pencil would provide a reflective quality which would highlight hidden written detail. This would assess RTI ability to see applied surface detailed rather than inscribed.
When viewed in default (image 1), the viewer can see a flat image of with no enhanced definition. When viewed under specular enhancement (image 2) surface detailing becomes apparent. Here we can see that the surface of the block has been deliberately prepared by using an implement to smooth the surface. Horizontal marks can be seen, possibly created using a knife blade. It is also possible to see that the actual pencil has partially inscribed the surface. With this render mode it is possible to see letters that have since lost some or all of the graphite. Under specular enhancement graphite did not reflect. However, when viewed with unsharp mask render mode (image 3) a high degree of contrast picks out the graphite from the chalk background.
This case study has shown that graphite does not show clearly on soft chalk. However, due to the soft nature of the chalk, it was possible to see inscribed letters as shallow grooves. 

If you can't see the video it can be viewed on YouTube here