In our second installment of our series on home photo framing basics, we look at acid-free materials: what they are, when to use them, and whether the “acid-free” label can be trusted.
In photo framing, the term “acid-free” is applied to those substances that have a neutral or slightly alkaline pH. This is important for conservation purposes as the acids in framing materials can cause degradation, yellowing, and brittleness of framed photographs. Some acid-free materials are acid-free by nature, while others have had the acids in them neutralized and/or a buffer added. (Buffers create a reserve of alkalinity in the material, which will react with the acids produced to create a neutral pH, delaying the onset of damage to a print from acid-containing materials.) Anything from mat boards and foam boards to the glue, tape, and even the ink used to sign or label photographs might be labeled “acid-free.”
When acid-free materials should be used is, to a certain degree, a matter of personal choice. Certainly a print that has significant monetary value should be framed using only acid-free materials. However, any print that you wish to preserve for many years, whether monetarily valuable or not, should be framed with acid-free materials as well, as these materials can add decades to the life of a print.
What causes acidity in the majority of framing materials? In short, wood. Lignin and other substances found in wood and wood pulp are major culprits in the deterioration of paper products. Newsprint, for example, still has most of the wood’s original lignin, and it is this lignin that is responsible for its rapid yellowing. Because most mat board and the paper coatings of foam board are, like most other papers, made from wood pulp, they too have lignin in them, unless it is first removed from the pulp. If the acids created by the lignin in a mat come into contact with the photograph, it will, over time, cause what is known as “mat burn,” or the browning of the print from the edges inward, as the acids make their way further into the interior of the photo. If the mounting board is not acid-free, it will eventually attack the entire photograph, “eating” the print from the back to the front.
Before we go any further, I should point out one inalterable rule of photo framing: under no circumstances should corrugated cardboard ever be used in any capacity during the framing process. It is highly acidic, and will do an inordinate amount of damage in a very short time. I have seen it used as mounting boards, as filler boards behind mounting boards, and as spacers between mats to create a shadow effect. Even as a filler board, with a mounting board between it and the print, corrugated cardboard is so acidic that its outgases will penetrate the mounting board and begin to damage the print in a matter of months.
What should you look for in acid-free materials? That depends largely on two considerations: how long of a life-expectancy you expect the print to have, and how much money and time you are willing to invest in your framing project.
There are varying degrees of “acid-free”. The highest quality materials are made from cotton rag paper. These are innately acid-free, as they are not made from wood pulp at all, but rather, as the name suggests, cotton fibers. Often referred to as museum- or archival-grade, cotton rag is generally the longest-lived of the mat and mount boards, and is available from most framing shops. However, it is not generally pre-cut and off-the-shelf, and it tends to be the most expensive of the boards; it therefore does not fit easily into the home photo framer’s arsenal.
Conservation-grade mats and boards are made from traditional wood pulp that has had the pulp acids removed, and the resulting paper is buffered. By some estimates, conservation-grade materials will last well over 100 years before damage begins. Conservation-grade materials may or may not be available in pre-cut sizes at your local frame shop. (In my experience, non-national chain frame shops, and frame shops that focus mostly on art and framing supplies, have a better selection of pre-cut, conservation-grade materials than national chains and larger craft stores.)
Mats and boards simply labeled “acid-free” are generally composed of three layers: an inner core covered on either side by a paper liner. These are the most common pre-cut, acid-free materials at the disposal of the home framer. Many frame shops will have a wide variety of pre-cut sizes and colors available, making them an easy choice for the home framer. However, these products are not as acid-free as the labeling would have you believe. In most cases, it is only the outer paper linings that have been treated to be acid-free; the inner core is made from the same material as non-acid-free boards. These mats and boards will provide some additional protection to your print in the short term, but the acids in the core will eventually reach the print through leaching and out gassing.
Do these drawbacks mean that these materials should be completely avoided? Absolutely not. These are the most readily available and least expensive acid-free mats and boards, and they suit many home framing projects perfectly – especially when you are not inclined to cut your own mats or pay to have a professional cut them for you. Anything of significant sentimental or monetary value should be framed with either conservation- or museum-grade materials, but it is perfectly appropriate to use the easily available, pre-cut, “acid-free” labeled materials on many other prints. It is up to the framer to decide the level of protection appropriate to each individual print. Let’s face it: not every image we want to frame and display needs the red-carpet treatment. If you do use these materials, you can help to extend their useable lifespan by sealing them with an acrylic matte finish, available at most framing and art supply stores. Make sure that you are in a well-ventilated area and spray the mats evenly and completely, especially the bevels and the edges where the core is exposed. The spray will slightly darken the mats’ surface, which is one reason an even coat is so important. Be certain to allow the spray to completely dry before using the mats; you don’t want to introduce any moisture into the interior of the frame. This technique will not give your print the equivalent protection of using conservation- or museum-grade materials, but by sealing the exposed edges of the beveled paper core, it helps to prolong the cleanliness of the frame’s interior environment – and thereby slow the degradation process.
In a similar vein, the rabbets of wooden frames should also be sealed, and for the same reasons. Most ready-made frames have the rabbets already sealed through paint or some other finish that coats the wood. Thus, the home framer rarely has to do anything at all to the rabbet. At times, however, the rabbet is raw wood. In these cases, to create an acid-free environment, the rabbet needs to be sealed with either some version of a wood sealant (shellac, paint, etc.), or aluminum frame-sealing tape.
Of course, to create and maintain an acid-free environment, any adhesives used must also be acid-free. Fortunately, with the rise of scrapbooking, the availability of acid-free (sometimes referred to as “archival”) adhesives has skyrocketed, while their prices have fallen. It is always a good idea to ask your local frame-shop professional about any particular adhesive you are considering, as their qualities vary widely, and each has distinctive pros and cons. Like the acid-free paper products, adhesives have a hierarchy of “acid-freeness”: true museum mounts use Japanese rice paper and rice-starch paste, but they can be challenging to work with and fall far outside the realm of the typical home framer. Linen tapes fall into the conservation-grade level, but they are generally thick and can leave impressions or grooves on the print being mounted. Acid-free paper tape is thinner and therefore leaves no grooves, but it is not strong enough to hold works of substantial weight, including mats. Adhesive sheets can be fantastic, but are not reversible. Mylar photo corners can be employed to safely mount the print, possibly eliminating the need for any adhesive at all, but they cannot be used to hinge mats to mounting boards. (They also come in a much greater range of sizes than most of us realize. They are not limited to the commonly found 1/2 inch-size, but rather are available in sizes all the way up to 3”. For even larger prints, mounting strips are available that can be cut to the desired size.) Spray adhesives, while useful for many framing projects, are not generally acid-free. Most household tapes and glues are not acid-free either, and/or they will react with the chemicals in photographic paper in ways that can harm the image. They should therefore be avoided. And as Vivian Kistler, an authority on conservation framing techniques, says, when it comes to using duct tape in your framing projects, “Don’t even think about it.”
Jodi
City Escapes Nature Photography, LLC
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