A Consumer Guide to
Created by Image Permanence Institute with support from Tru Vue
Materials for Preservation
Framing and the Display
of Photographic Images
(click any picture to see a larger picture)
FORCES OF PHOTO DECAY
Decay on Display
Most people think that light causes most of the damage to photos on display, but there are other forces that contribute to the decay of photographs, including heat, pollution, moisture, and even the framing materials themselves. Below are descriptions of each of these, but we will start by discussing exactly how light harms photographs.
The rate at which photographs are damaged on display and the type of damage that appears are determined by two properties of light: quality and quantity. Light quality doesn't refer to how well the bulb was manufactured or how long it will last before burning out, but to the type of light: tungsten, fluorescent, or sunlight. Quantity of light refers to its intensity, that is, how bright the bulb is. The light from a child's nightlight is similar in quality to that from a hundred-watt lamp bulb, but the quantity of light emitted by the nightlight is far less.
The quality of light is often correlated with the color of light. Most people know that tungsten light tends to be yellow and that fluorescent light is fairly white (although older bulbs often made things look green). Sunlight varies in color throughout the day and with different types of weather. Sunsets are marked by their glowing orange, while an overcast day can look dark grey-blue. The color of light affects both the way in which photos on display change and the speed with which they change. Blue light is higher in energy than green, yellow, or red light, and the higher the light energy, the more likely it is to damage photos. Right next to blue light in the spectrum (see Fig. 7) is ultraviolet (UV), which can be the most damaging of all. The term UV light is really a misnomer. The word light applies only to the energy that we can actually see, and UV is invisible to humans (although some animal species can see in this range).
It is more appropriate to refer to UV energy. Next to red in the spectrum is infrared energy. Infrared is less damaging in terms of its light energy, but it can
Damage by UV Energy
Each type of light (tungsten, fluorescent, or sunlight) contains different amounts of UV energy. Sunlight contains the highest UV levels and is the most damaging, followed by fluorescent. Tungsten carries very little UV energy.
UV energy can damage photos by fading the image as well as yellowing and/or embrittling the paper. One of the ways it fades photos is by breaking the internal chemical bonds of the color molecules that form the image. This causes the molecules to become colorless and invisible to our eyes. The more this happens, the more the image fades. This process is called photolysis.
Another way that UV energy fades photos is by photo-oxidation. UV energy excites the color molecules, making them more sensitive to oxidation (the same process that causes iron to rust). This is a two-step process (excitation-oxidation) that won't take place without both UV energy and an oxidizing agent. Unfortunately, our air is full of oxidizing agents, most notably ozone. Both photolysis and photo-oxidation can cause photographic prints to yellow or become brittle over time (see Fig. 8).
Tungsten lighting emits fairly low levels of UV. Because of this, many people mistakenly believe that, since they light their homes with tungsten bulbs, they don't have to buy UV-blocking glazing for their frames. However, research by a major manufacturer of photographic prints has shown that the dominant type of light in homes is still sunlight through window glass.(1) This means that the photos we display are actually being subjected to the harshest of type of light and therefore really do need protection.
Damage by Visible Light
Visible light (non-UV) can also be damaging to photos. Visible light usually isn't strong enough to cause photolysis, but it can still cause some photo-oxidation. So, while it is very important to reduce a photo's exposure to UV energy, that won't prevent all fading. We can reduce damage by visible light by reducing the quantity of light, and we can do this by placing our framed photos in low-light areas or by moving photos and light sources further away from each other. Because our framed photos must be exposed to some visible light if we want to see them, it is all the more important to reduce any damage from UV energy or poor-quality framing materials.
Damage by Infrared Energy
Like UV energy, infrared energy exists in varying amounts in each type of light. Tungsten and sunlight have more infrared than fluorescent. As mentioned, infrared energy can heat framed photos. This can dry out the photograph, causing it to warp or shrink and pull at its mounting points. Heat also accelerates other types of decay. It sometimes takes longer to notice damage caused by heat than to see damage caused by UV or visible light, but the damage is always occurring, even when UV-protective glass is used. Again, keeping framed photos in naturally low-light-level areas in the home will reduce the amount of damage over time. If tungsten light is aimed directly at a photo, feel the glazing for warmth. If it feels hotter than other areas of the room then lower the light levels or move the photo and the light source further apart.
While light fading is easy to describe, dark fading is more complicated. Dark fading is the damage that occurs when photos are stored in the dark, as in boxes or photo albums. Where it gets confusing is that dark fading also occurs in the light, simultaneous to light fading, so it's always happening to our framed photos too. Dark fading is not caused by the dark; it is the sum of the damage caused by forces that do not need light, and those forces continue whether the lights are on or off. The forces behind dark fading are heat, pollution, and humidity.
The heat that damages photos is not the kind of heat we associate with an oven or even a very hot day. Room temperature for us is hot for a photo. Most photos last longer when stored in cool or even cold storage spaces. Since we prefer our living conditions to be around 70 to 75 degrees, the lives of our photos are forcibly shortened. There's really not much we can do to prevent this for our photos on display. The one thing we can do is make sure that the lighting we use to illuminate our pictures does not also heat them up.
Pollution in the air can come from outside the home in the forms of ozone, oxides of nitrogen, and other gases that are the products of our industrial society, but pollution can also come from sources inside the home, such as household cleaners, electronic equipment, and curing paint and adhesives. Don't clean your frames with chemicals, and always let a freshly painted room cure for at least two weeks before rehanging your pictures. Pollution was the cause of the image fading shown in Fig. 9.
Damage by moisture comes in many forms. In the case of framed images, one of the most common and the most destructive is blocking, which is the adhesion of a smooth surface - in this case the glazing - to the surface of a photo. In high humidity the top layer of many photos can soften and become like glue, bonding the photograph and the glazing together. It is often impossible to remove a blocked photo without destroying it (see Fig. 10). This is why it is so important to use a window mat or frame spacers to prevent direct contact between photograph and glazing.
High humidity can also result in mold growth that damages the image (Fig. 11). Mold is also a health hazard. If mold growth is not too severe, a professional conservator can remove it. The dyes used in some modern digital photos have a tendency to bleed at high humidity. Details in the image will blur, making the photo look out of focus (Fig. 12); the colors can shift as well.
Damage from Poor-Quality Framing Materials
The materials used to frame a photograph can also cause damage, if they are of poor quality. Usually, the worst culprits inside the frame are the paper materials that make up the mat board, the window mat, the filler board, or the backing paper. These can fade, mar, or yellow the photo.(2) Wood frames and some adhesives can also cause damage.
The reactions caused by these materials, like those we see from air pollution, are often oxidation reactions that result in image facing. In a black-and-white image the faded silver can migrate to the surface of the print and be converted back into metallic silver by other pollutants (either from the framing materials or the air), forming a mirror-like sheen on the print's surface. In the case of the photo on the left (Fig. 13), a poor-quality mat covered the outside edges of the print and caused the silver mirroring. The oval shape in the center of the print is where the mat did not cover the print. Often this form of damage is caused by papers that contain lignin. Lignin is a natural substance in wood that, if not removed during pulping, can be very hazardous to photos. Not only can it cause fading or mirroring like the example shown here, but it can also cause severe yellowing of photos.
It is not always the image that is damaged; sometimes it is the paper support. Acidic mat boards, filler boards, and frames can "burn" paper, causing it to turn brown and become brittle (Fig. 14). A photograph with this type of damage must be handled very carefully to void breakage. All of these problems can be prevented by selecting good-quality framing materials to begin with.
Some photographic materials themselves can give off harmful chemical gases that turn around and cause further damage to the photo. This is called autocatalysis, because the photo catalyzes its own decay. Any photo printed on a poor-quality paper or unstable plastic can deteriorate and release chemicals that then accelerate decay.
Not only to the different forces of decay described so far occur independently, they also exacerbate each other and make the damage even worse. The framed photograph and detail in Fig. 15 show what has often been called the "picture-frame effect." This black-and-white photo was framed and displayed on a wall in an office. UV energy entered the frame and reacted with one of the layers of the photo creating a pollutant that then faded the image. The faded silver was then converted into an orange substance in the dark areas of the print by yet another pollutant that came from either the photo itself or the framing materials. In order to occur, the effect needed UV energy, an unstable print, the pollutants, and the closed environment of the frame. Removal of any one of those factors could have prevented the damage we see.
Thus an important point to remember regarding the ways in which photos are harmed when framed and on display is that the damage to the photograph isn't always caused by light or UV energy. Damage can also be due to the framing materials, moisture in the air, pollutants from a variety of sources, and sometimes all of the above.
BEST PRACTICES FOR FRAMING
This document can be found in PDF format at http://www.imagepermanenceinstitute.org