The powder samples measured in this work were SiC (nanopowder, <100 nm particle size, 594911-100G, Sigma-Aldrich), TiO 2 Rutile (204757-25G, Sigma-Aldrich) and MgO (307742-500G, Sigma-Aldrich). The three powder samples were mounted into separate glass pipettes with an outer diameter of ca. 7.5 mm supported by quartz wool from both ends. Two pipettes were prepared using the same MgO powder sample. The four glass pipettes containing the powder samples were mounted onto a 3D printed sample holder designed for the parallax experiment. Photographs of the experimental setup can be found in our previous work .