If you have stopped by to look at our Victoria Theatre exhibit on the first floor of Dunbar Library, you may have noticed a little blue card in the corner and wondered, Oh, hey, what is that little blue card? Is that part of the exhibit?
The cards are usually known as Blue Wool Fade Cards, Blue Scales Textile Fading Cards, sometimes simply Blue Wool Cards, or some variation thereof. The card’s purpose is to help us gauge the potential for light damage to materials in a particular case or area.
Have you ever moved a stack of papers on your desk and found that a colorful sticky note that was halfway under the papers now has a noticeable “line” where the previously covered-up part is darker than the part that was exposed? Or taken a framed, matted photograph off the wall and out of its matte and noticed that the portion that showed through the “window” of the matte is faded, compared to the edges that were covered by the matte?
These are commonly encountered examples demonstrating the damaging effects that light can have on materials. Light exposure can cause fading, a damage that we can see with our eyes, but in some materials it can also damage an item’s physical and chemical nature as well. Both natural light (sunlight) and artificial (electric) light can have damaging effects. The duration and intensity of the exposure also factor into the amount of damage caused.
To get a sense of the amount of light damage to which an area is exposed, we place one of these Blue Wool Cards into the case, with part of the card exposed and part of it covered up. We check the card periodically — in this case, we’ve been checking it weekly — to see which, if any, of the colored cloth swatches on the card are fading. The different swatches provide a sort of scale (conforming to ISO 105-B01), with the lighter swatches being more susceptible to light damage, and the darker ones on the other end, less so.
You know they say a photograph is worth 1000 words, so here are two photos to compare how the card in our exhibit case looked on the day it was installed (Feb. 9th, top image), versus how it looks today (April 6th, bottom image):
Some light damage is clearly visible in the bottom photo on the right-most color swatch. Notice how the top of the swatch has faded, losing some of its blueness. This tells us that even in a short 2 months, light damage is possible. (We have been checking every week since February 9th, and as a matter of fact, this strip was showing signs of fading after only 1 month!)
There are a lot of scientific factors to be considered when judging the usefulness of this data — such as how the fade-susceptibility of that particular wool swatch dye corresponds to the fade-susceptibility of actual archival materials — but you get the idea!
And how you know what that little blue card is for!
For more a much more detailed and scientific explanation of why archival materials must be protected from light damage, see the Northeast Document Conservation Center (NEDCC)’s leaflet 2.4: Protection from Light Damage.