This series is used as NIST traceable calibrants or controls for instruments requiring a higher density and more contrast to incident radiation than that provided by the polymer microspheres. The microspheres are made of soda lime glass which has trace amounts of metallic elements. This makes them easily detectable by non-dispersive X-ray methods and improves their contrast and reflectivity in optical, ultrasonic and electron beam detection methods. Most of the non-spherical and broken particles have been removed, assuring a high percentage of round spheres. They are packaged as dry powders in 1 gram bottles. The soda lime microspheres have a density of 2.4-2.5g/cm3 and an index of refraction of 1.51 @ 589nm. The softening temperature is 720°C and the dielectric constant is 7.3 @ 1 KHz and 20°C. Brands: Thermo Scientific