These low cost filters provide blocking via absorption of light within the glass itself, causing their spectra to be composed of broadly varying regions of moderate transmission and blocking.  Absorption is proportional to path length through the filter, allowing these filters to be used additively at the expense of transmission.  A wide selection are available from stock, and on a quick-turn semi-custom basis in a variety of glass types, thicknesses, and sizes, including 2 in squares.  Color glass filters are not recommended for use with high power pulsed lasers, though they are capable of withstanding up to 25 W/cm2 of continuous wave power.   Longpass color glass filters are useful for low power laser line cleanup, spectroscopy, short wave blocking and order sorting.  Note that typical internal transmittance curves are for a specific thickness and may not consider reflectance losses at the surface.