Radiation curable compositions for additive fabrication processes, the components cured therefrom, and their use in particle image velocimetry testing methods are described and claimed herein. Such compositions include compounds which induce free-radical polymerization, optionally compounds which induce cationic polymerization, a filler constituent, and a light absorbing component, wherein the compositions are configured to possess certain absorbance values at wavelengths commonly utilized in particle image velocimetry testing. In another embodiment, the compositions include a fluoroantimony-modified compound. Such compositions may be used in particle imaging velocimetry testing methods, wherein the test object utilized is created via additive fabrication and is of a substantially homogeneous construction.