Zinc selenide (ZnSe) is a widely used ATR crystal material and is a relatively hard and brittle material. It is insoluble in water but is attacked by strong acids and bases. ZnSe has a good mid-IR spectral range reaching to about 630 cm-1 for multiple reflection ATR crystals at the long wavelength side of the spectrum (depending upon IR beam pathlength). Coated versions of our ZnSe ATR crystals are available for improved IR throughput and enhanced seal within the ATR crystal plate.