Since starting at Allen Archaeology in September I’ve been involved with expanding our potential for digital recording and imaging. As you will hear in a later post, AAL have been using some techniques on site for a while but had not experimented with Reflectance Transformation Imaging (RTI).

A photo taken under normal lighting conditions

The same piece of wood viewed under novel lighting conditions and an acute lighting angle making the surface marks clearly visible

RTI is a technique which allows multiple images to be manipulated under varying lighting conditions to capture subtle surface information. Put simply when a surface is illuminated from an extreme angle it shows different information to a surface lit from above. By taking a series of photos from a single position but lit from different angles the images can be combined into an RTI, capturing a very accurate record of a surfaces shape. Imagine turning something in the light to discern changes in the surface. It can also allow the object to be viewed under novel lighting conditions allowing further information to be gleaned. Internet Archaeology have developed an online viewer with some examples here.

RTI has been used in research to record and study a whole range of objects and surfaces. Conservators have found the records useful in assessing the condition of artefacts (see here for some examples from the Smithsonian). While specialists in other fields have found the ability to compare artefacts located around the world has allowed their research to evolve (here are a variety of examples).

A normal visualisation of a Saxon pot from one of our sites

A close up of a coin under specular enhancement

At Allen Archaeology we have been using RTI as a supplementary record to photogrammetry, recording some of our particularly special finds. The results can then be sent on to our specialists to help them prepare our reports or to researchers with an interest in particular finds. They can also be used for us to send detailed information to our conservators in advance of the actual objects, helpful where objects are particularly fragile.

Chris and Josh having a go at capturing an RTI

The joy of RTI is it is quick, simple and low cost. The only equipment needed is a camera which can be used on a manual setting, a shiny ball (which the software uses to identify the position of the lighting) and a way of moving the lighting conditions (this can be a fancy remote flash or a light from a mobile phone). The software to combine the images is freely available (via the Cultural Heritage Imaging website).