 dark room development), as opposed to computer printing, are already slightly acidic by nature and therefore are much less likely to be damaged by non-archival mats.In addition, correct "conservation" framing includes all components, not just the mat board used directly behind the glass.Until recently, there were no truly "archival"-quality foamcore boards available, though a number of foamcore brands exist with buffered surfaces and the Nielsen Bainbridge company now produces one that is claimed to both block the intrusion of airborne pollutants and to avoid the problem of outgassing that non-archival foamboards may fall prey to; for this reason, and due to many smaller frames' shallow depths, it is not uncommon to see mat boards used as backing for a picture frame as well, though foamcore and mounting boards tend to be stiffer.