(a) Photograph of the sample cell showing the interface between castor oil (subphase) and the Li-Fht clay suspension in silicone oil. The red dashed and continuous lines represent the direct and reflected beam, respectively. (b) Detector image showing one snapshot of the direct (refracted) beam and the reflected beam. (c) Reflectivity recorded from the oil–air interface, which is not expected to have a critical edge and the intensity axis has no absolute normalization. The inflection point seen in the curve is likely to be due to contamination of the measured reflectivity from the direct beam as the angle is reduced and the two spots on the detector converge (data reduced using the RODAN package with DAWN at Diamond).