A simple schlieren technique is used to visualize strong gradients of refractive index in liquids under atmospheric conditions and elevated pressure. The gradients are mainly caused by concentration differences within a thin liquid sheet. A simple system using Matlab and open source applications is designed and applied to demonstrate the challenges and limitations of a quantitative approach for strong gradients in liquids. Possibilities for the optimization regarding the detection of strong gradients are shown, but rather qualitative than quantitative results are obtained.