The pH measurement runs on a scale of 0 to 14 and reflects the relative level of acidity or alkalinity of the material being measured. In the case of picture framing, the pH measurement is an important consideration that will affect the longevity of the item you are framing. A rating of 7.0 (plus or minus .5) is considered neutral. As the pH shifts lower on the scale, it means the material is more acidic; as it shifts higher than the neutral range, then the material is more alkaline. As the scale shifts by one numeric value, for example from 6.0 to 5.0, the level of change in the acidity is 10 fold higher, and a 2 point change on the scale indicates a 100 fold shift in acidity or alkalinity. It is important to realize that even small pH changes can be significant.
When selecting matboard or backing materials for valuable art or documents, be sure to ask your framer or check the manufacturer’s specification sheet for the pH value and recommended use. Because many popular “decorative” mat boards contain buffers that make them “acid-free” or “neutral” for a period of time, you must refer to these specification sheets (or look for the imprinted information on the back of the matboard sample) to identify conservation or archival products in cases where preservation is important. This is because some materials within a standard “acid-free” board, such as lignin, become more acidic over time—causing pH shifts that discolor the core of the board (making the bevel appear yellowish.) Gradually, this change will cause the same discoloration and brittleness in your framed art or document. External pollutants can also contribute to pH shifts in framed pieces over a long period of time, so starting with properly engineered materials and using professional framing techniques are very important.
To locate a reliable custom framer, look for the “Certified Picture Framer On Staff” designation, which indicates the person has been certified in proper framing and preservation techniques by the Professional Picture Framers Association (PPFA). Through their Web site, PPFA offers a “search” option to help with locating a reputable framer (try http://www.ppfa.com/ and then look for the “Find A Framer” link.)