One of the most frequent but difficult graffiti forms to record during the project were light engravings that had been subsequently whitewashed. This was particularly an issue if they were relatively large or located in dark corners of cells. Thankfully, the majority of engraved graffiti was created to be seen and therefore was located where direct light would hit the wall and they were deep enough to allow a shadow to reveal the engraved form.
If this was not the case then the engraving could be almost impossible to see nevermind photographically record. This occurred in a number of cases and after discussions with the Discovery Programme – a government-funded archaeological organisation – it was decided that they would temporarily expand their 3D icons project to include Kilmainham Gaol as the only modern, standing building that would benefit from a limited number of overview and specific 3D scans.
A number of techniques were employed during the course of the two days that the Discovery Programme visited Kilmainham Gaol to scan graffiti. It became clear quickly that the less detailed overview scans – including high-resolution object laser scanning – would not reveal graffiti but did show uneven walls where lumps of plaster had fallen and then been subsequently painted over. This includes this example from the cell that Patrick Pearse had been held in 1916:
The most successful technique in revealing this graffiti was Reflectance Transformation Imaging (RTI). Extremely subtle incisions on the wall’s surface was recorded using this technique, in many cases subtleties were recovered that would be difficult to see by naked eye. RTI images were created by taking multiple digital photographs of the area being recorded. The camera was placed on a tripod to ensure it did not move and remained completely stationary whilst all images are taken. The variable in recording was the change in the light direction by using a wireless flash that moved around the focus on the wall mirroring the hands around a clock face. A minimum of 36 images were taken and then combined using a software package called RTI builder. A mathematical model was derived that allowed the creation of a 2 dimensional output whilst controlling the light direction digitally.
The recording over two days in Kilmainham achieved amazing results. Details that were not apparent during the original recording process became clear in the digital processing. Subtle detail became evident, especially in the example of a soldier that was very difficult to determine details due to the dark environment of the corner of the cell, the lightness of the engraving and the size of the figure. The general shape of the graffiti could be made out, but the details of his outfit and features could not be seen until the lighting was digitally manipulated and the texture of the surface removed. The level of detail apparent in the RTI image may allow us to identify the regiment due to the uniform particularities (as well as the kilt hinting at a Scottish regiment).
This two-day collaboration marked an important point in the project. It occurred in March 2014, six months after the official photographic recording of the site had ended. This meant that the graffiti locations were known but the limitations of photography had become apparent. This collaboration allowed the Discovery Programme to test the boundaries of their technology and applicability to more modern structures and also allowed the recording of otherwise overlooked graffiti for the graffiti project. It remains an important option for retrieving almost lost graffiti and hopefully will be expanded on in the future.
McAtackney, L & G Devlin. 2014. Recovering Revolutionary Ireland: graffiti recording at the West Wing of Kilmainham Gaol. Archaeology Ireland.