Firecrest ND is a revolutionary new type of ND filter from Formatt-Hitech. Rather than dyed resin, Firecrest is a rare earth mineral coating used to create hyper neutral NDs. The filters are made from 4mm thick Schott Superwite glass, and the multicoating is bonded in the middle to increase scratch resistance. Firecrest Filters are neutral across all spectrums, including UV, visible, and infrared.Firecrest ND is a quantum leap improvement over all previous generation ND and IRND products and represents the technological state of the art in scientific light modification. These glass filters are hyper-neutral across the visible light spectrum and also remove more IR contamination than any other filter - making them IRND filters. Firecrest is a radical departure in how ND filters are manufactured. Previous generation NDs were made by dying resin. Firecrest is not a dying process, it is a rare earth metal coating process that is applied directly to the glass through an electrolytic process.On rectangular filters, the Firecrest coating is sandwiched between the finest Schott Superwite optical glass, increasing scratch resistance and longevity. Firecrest reduces all spectrums of light (UV, visible, near infrared and infrared) almost perfectly evenly.