Optical Characterization of Transparent Gelita Using the Modulation Transfer Function

Visualization of internal geotechnical processes in physical modelling is possible through the use of transparent soils. These materials rely on optical clarity hence a systematic impartial user-independent assessment framework for visual quantification is necessary. The visual quantification of transparent soil models have been traditionally done by Snellen eye charts. Black and Take (2015) introduced an independent method called modulation transfer function (MTF) to quantify the visual quality of transparent soil models. This method incorporates optical calibration charts consisting of black and white grids of different spatial frequency (pixel intensity). A new transparent material named Gelita is introduced to model clay and assessed using this standardized framework. Different mixture ratios of transparent Gelita (5% to 20%) are produced and visually tested. Viewing depth is varied from 50 mm to 150 mm and tests are repeated to quantify this effect on the visual transparency of Gelita. It is found that smaller mixture ratios of Gelita have the highest MTF and therefore offer the highest optical quality. The effect of viewing depth is more pronounced in samples of Gelita of larger mixture ratios. Re-use of the material by secondary melting does not significantly affect transparency regardless of the mixture ratio.