Pulverized and sieved powders were then loaded into evacuable, stainless steel die sets (~12.7 mm diameters) sandwiched between two polished stainless steel spacer pellets and placed onto uniaxial presses. Die sets with perovskite powders were dried under vacuum for ~1-2 hours prior to application of pressure. Three pressure stages were applied under dynamic vacuum at room temperature (~21±2 C). The first two lower pressure stages (35 MPa for ~1 hour and 150 MPa for ~2 hours) were used to produce an opaque green body compact (see Figure ). Then, select finishing stage pressures between ~200 and ~525 MPa were set for ~150 to ~300 hours. Finishing stage pressures and press times depend on the thickness of the ceramic (see SI for further uniaxial pressing details). Finally, perovskite ceramics were carefully removed from the die sets. All ceramics were characterized thereafter without any additional annealing or polishing steps. Transmission measurements were performed with a Cary 5000 UV-Vis-NIR spectrophotometer. Metal plates with ~4Ø mm apertures were placed in the light path between the sample and detector to limit forward scattering from being quantified as transmission. Of further interest is perovskite ceramics' transmission at longer wavelengths. Figure plots transmission spectra from 0.3 m to 25 m for the l=0.989 mm MAPbBr3 ceramic along with other commercially available transparent polycrystalline ceramics-ZnSe, ZnS, Al2O3, and YAG-for comparison. While CH3NH3 + vibrational absorption is prevalent throughout the infrared, high transparency windows are observed from ~2.5 to ~3.0 m, ~4.2 to ~5.2 m, and ~12 to ~20 m. Such windows may make lead halide perovskite ceramics appealing host materials for rare-earth dopants in perovskite ceramic-based solid-state infrared lasers. Details on transmission measurements and max transmission calculations can be found in the SI. nm to ~30 nm for all ceramics and are significantly smaller than the ~550 nm to 2000 nm wavelength range of interest (/100≲Sq≲/20). Thus, surface roughness should have minimal contribution to transmission losses observed in Figure . Interestingly, perovskite Sq values reflect that of the polished stainless steel spacers surface roughness (Sq~15 nm) that are in contact with the perovskite ceramic surfaces during uniaxial pressing (see Figure ). This surface mirroring effect is likely due to plastic deformation of MAPbX3 perovskite grains, causing them to conform to much harder (pre-polished) stainless steel spacer surfaces during densification. Further improvements to perovskite surface roughness may therefore be possible by polishing spacer materials down to Sq<10 nm. This would eliminate the need for post-processing (e.g., polishing and cutting) of perovskite ceramics to attain optical grade surface quality straight out of the uniaxial press.