  Radio, millimetre and sub-millimetre astronomy experiments as well as remote
sensing applications often require castable absorbers with well known
electromagnetic properties to design and realize calibration targets. In this
context, we fabricated and characterized two samples using different ratios of
two easily commercially available materials: epoxy (Stycast 2850FT) and
magnetite ($\mathrm{Fe_{3}O_{4}}$) powder. We performed transmission and
reflection measurements from 7 GHz up to 170 GHz with a VNA equipped with a
series of standard horn antennas. Using an empirical model we analysed the data
to extract complex permittivity and permeability from transmission data; then
we used reflection data to validate the results. In this paper we present the
sample fabrication procedure, analysis method, parameter extraction pipeline,
and results for two samples with different epoxy-powder mass ratios.
