Replicating master gratings on Pyrex®, produces diffraction gratings with flatness, λ/4 or better, good thermal stability and resolution equal to 80-90% of the master. Thermally stable diffraction gratings are available in groove spacings from 120 to 1800 g/mm, blazed from 240 nm to 12.0μ. These diffraction gratings are also available replicated on Zerodur®.