There are many different levels of archival mat boards. The lowest level are paper mat boards which are considered suitable only for "decorative" framing, not conservative framing. A level up from that are mat boards mat of alpha cellulose. The Bainbridge Alphamat is such a mat board. It is acid and lignin free, and uses Artcare technology that allows it to actually neutralize acidic compounds entering the framing package. It is a little more achival than most other alpha cellulose mat boards. It is laminated with a color surface paper that has dye's that you would not use for museum quality framing but the surface paper is not in contact with the print. This is also the reason that the bevel on the core is not the same color as the surface. The primary mat board being referred to was the Bainbridge Alpharag Pearl White. This is the highest level of protection you can get, and a little better than the Westmister which is also very good. The Alpharag board is composed of cotton which is naturally inert. The board is acid free, lignin free and only very safe dyes are used. That is why the color selection of the musuem rag mat board is so limited and you never see any bright colors. It is also treated with the Artcare process and since Bainbridge purchased exclusive rights to the technology no other mat board companies can offer it. This board is composed of cotton layers that are dyed which is why the color will be uniform from the surface to back. All of these mat boards are buffered with calcium carbonate which helps make them even less acidic. Paper mat boards are often buffered also and then sold as acid free, however, since the substrate is naturally acidic they will return to being acid when the buffering wears off. I dont know how long that takes, but the general guideline I have heard is that if you want it to last longer than 5 years with no noticible damage, do not use paper mat boards.
Originally Posted by jeffreyg