If there is one thing that always seems to come up in conversations about framing, it is “acidity.” Is the adhesive acidic? Are the boards pH neutral? Do they need to be buffered? Is this alkaline? Is it too alkaline? What is alkaline? Why do we care?

Stick to the middle

To begin, let’s look at the ph scale up-close and personal. Starting on the left side: something with a pH level of 0 is the most acidic, something “in the middle” at 7 is pH neutral, and something on the far right end of the scale, at 14, would be alkaline. To put this into perspective, lemon juice is about a 3 (fairly acidic,) while bleach is around 12 (quite alkaline.) Water is 7, pH neutral. Acids will break down the fibers in paper products, causing yellowing and brittleness, and certain alkalis will do the same. (Think of that spot of bleach on your favorite cotton tee that became a gaping hole after a couple of washings.)

Seem pretty simple so far? Let’s look a little deeper.

 

Peer Pressure

Materials will have a natural pH level, but this can be accidentally or purposely altered. Since 7 is neutral pH, picture framing standards require that materials labeled “pH neutral” fall between 6.5 and 7.5. If a material contains lignin, it must have the acid neutralized in order to fall in that 6.5 to 7.5 range at the time of manufacture. The acid can be neutralized with a buffering agent such as calcium carbonate, which is the ingredient in the oral Antacids that we take. Just like our Antacids, this is a temporary fix and wears off over time.

If a material is lignin free, and therefore acid free, it can be contaminated by other acidic materials, which will also change its pH level. For instance, a cotton artist’s paper is naturally acid free, because it contains no lignin. If it is mounted and matted in wood pulp boards, the acids from the wood pulp will eventually migrate into the cotton paper, damaging it. Acids can also be found in the frame, the fillets, the air inside of the frame package, the oils on our hands, and the adhesives used. These can all end up on the valuable work of art that they are meant to protect.

 

Too much of a good thing?

It’s probably obvious by now that if a matboard is acidic, it is buffered in order to bring it up to a safe, if relatively temporary, pH level. It may also seem fairly straight forward that it’s desirable to have a “reserve” of the buffering agent stored away in the matboard to counter other acids floating around inside the framing package, or on the art itself.

The amount of the reserve, however, must be carefully controlled to safeguard against damage to the art from too much alkalinity. It has been determined that the optimal range for the alkaline reserve is between 2% and 5%. Most materials are most “comfortable” in an environment that is essentially pH neutral, but that has a minimal amount of alkaline reserve to counter other acids present in its environment.

If the pH level rises too far past 9.5 because of the reserve, there is a risk that the artwork will degrade just as it would when in contact with acids.

 

To B or not to B (…Buffer, that is)

There are some materials, however, that prefer a low-alkaline environment, because they are extra sensitive to chemical reactions from contact with the buffering agent. These items consist either partially or entirely of protein-based fibers such as silk, wool or leather. Other not-so-obvious offenders are older photographs with protein-based emulsions and casings. These special photos are harder to identify, so it is best to use a non-buffered board on any photograph that is suspect.

There are only a handful of matboards that are left unbuffered, and they only exist in the cotton category. If an item is so delicate that it requires low-alkalinity, it will also require the highest quality of lignin-free board, so there is really no need to offer this option in anything but cotton.