In order to test and improve opacity models, we are performing experiments to accurately characterize and measure the opacity of high‐Z plasmas. In the experiments the NOVA laser at Lawrence Livermore National Laboratory is used to indirectly heat tamped thin foil targets containing mid to high‐Z ions of interest which are co‐mixed with low‐Z ions for spectroscopic determinations of plasma conditions. One of the NOVA beams is used to create a source of x‐rays for backlighting the plasma face‐on, while another beam is used to perform a radiograph of the expanding sample edge‐on. X‐rays that pass through and around the plasma are simultaneously measured on high resolution crystal spectrometers, and the opacity is measured by comparing the direct and attenuated x‐ray spectra. Plasma density is determined from the spatial extent of the expanded plasma, and plasma temperature is inferred from the ionization distribution of the low‐Z ions doped in the plasma. Predictions of the high‐Z opacity are then compared with data using measured conditions as input. These are the first high temperature opacity measurements in which sample conditions are simultaneously determined. We present measurements and predictions for a spectroscopic experiment using a comixture of aluminum and niobium. We discuss plans for future improvements, and for spectroscopic measurements in the spectral region determining Rosseland mean opacities.