The Lost Art - Detailed geological outcrop mapping using watercolour sketches

Field sketches are a fundamental tool for geoscientists in both research and learning. Field sketches are a helpful tool for expanding understanding and data sharing. When on fieldwork researchers and students find that perspective, weather, and lighting can all distort the view - highlighting features differently, changing colours and shapes to both highlight and conceal features of interest. Before photography was main-stream field sketching and indeed in-field watercolours were the norm for all field researchers. Sketching made observers look more carefully as well as better communicate their findings to others. Geologists in the 1880s were armed not only with hammer and notebook, but a watercolour palette to capture their field observations.      

Here we present a simple interdisciplinary workflow for using sketching and watercolour in addition to digital photography, to capture field observations and to spatially locate data collected. Watercolour paints are made of pigments suspended in a water-based solution, this means they are activated by water and dry quickly allowing fast composition. The paints are widely available as pencils, tubes, and solid pans at a range of different qualities and colours, which can be mixed and matched to mirror the colours of rock types. Watercolours layer well with pencil and pen for note taking and large sketchbooks can be filled easily with washes of colour that capture the essence of outcrops and landscapes. 

This combined methodology of sketching and watercolour with digital photography and ultimately the creation of a virtual outcrop model was used to study fault linkage in a multilayer of sandstones and siltstones at Calafuria, Italy over 5 days. The watercolour sketches produced are clear and legible panoramas of the outcrop with geological data and measurements geospatially annotated onto the outcrop sketch. Simple lines and colours have been used to emphasise important details, and although the sketches are not to scale, they are easily matched with the digital photographs and virtual outcrop away from the field. 

The sketches work to make the complexities of the outcrop more legible, enabling dialogue between researchers and adding to the resource of field data available for interpretation. Field photographs are affected by perspectives and lighting, and the quality of a virtual outcrop created from digital imagery is dependent on these factors as well as their subsequent processing. What we can see easily when we sketch as the light changes can be obscured permanently by a shadow in a digital photograph. Photogrammetry may add precision in measurements, but not necessarily the accuracy of interpretations. Perhaps most importantly when we observe and sketch, we concentrate on capturing details with geological importance and promote interpretation decisions such as the continuity of a fault that a camera does not pay attention to. We find the combined approach outlined illuminates the geology to create a much richer dataset than a photorealistic virtual outcrop alone.