Optical glass is generically requested for custom elements, Safetyrich uses normal quality BK7, a high quality optical glass that is used whenever the additional benefits of fused silica are not required.  Since BK7 performs well in all chemical tests, no special handling is required, thus reducing manufacturing costs. It is a relatively hard material with extremely low bubble and inclusion content. BK7 provides excellent transmittance through-out the visible and near infrared spectra and down to 350 nm in the ultraviolet.