Learn to Measure the Amount of Light Your Collection Has Been Exposed To – Part 1
In one of my previous posts about light and its harmful effects, I asserted that exposure of your baseball cards, comics, stamps and other paper based collectibles to seemingly small amounts of ordinary room light can cause fading of your collection. In this post I will show how it easy to quantify such fading without having to use expensive electronic instrumentation.
Our discussion begins with the “Blue Wool” cards below, which many museum curators use to estimate the effects that museum lighting has on various pigments, dyes, paints, papers, and other non lightfast materials. The Blue Wool cards comprise a set of horizontally dyed stripes. What is of particular interest about the blue wool cards is that the light fastness of the pigments of the dyes in the stripes can be used to mimic that of many items of history, and value, for example, stamps and art. By placing the cards/stripes at desired locations, the cumulative fading effect of any light in the vicinity of the cards can be visually quantified.
It takes about 3 times the amount of cumulative illumination to fade each stripe as the stripe that is directly above it. For example, depending on geographic location, season, humidity, the 3rd stripe from the top will begin to fade after exposure to about 3.6 Megalux hours of illumination, the 4th stripe from the top will begin to fade after exposure to about 8-10 Megalux hours, and the 5th stripe after about 30 Megalux hours.
The middle blue wool card above shows a lengthwise left section protected from all light by aluminum foil (Al), a middle section that is not protected at all, and a lengthwise right section that is protected with an ultraviolet (UV) filter. The right blue wool card shows the aluminum foil and ultra-violet (UV) filter removed after the dyed stripes on the card were exposed for 8 months to the light of a south facing Canadian window.
Comparison of the middle section of the middle and right card above against the corresponding right section illustrates one point that your beach going experience should have taught you; that exposure to ultraviolet UV light should minimized, which in the case of paper based collectibles can be accomplished via use of UV filters.
A more important philatelic observation is this: even when when protected by ultra-violet UV filters, your stamps and paper based collectibles can be damaged by the visible light component of light. This is the reason the right sections of the middle and right blue wool cards above show fading. Why? … because of something many collectors fail to consider … that UV filters DO NOT filter VISIBLE wavelengths of light.
However, the most important take away is this: although blue wool cards above show that filtering of ultra-violet light does indeed reduce fading and damage, they illustrate that every time VISIBLE wavelengths of light are used to view your philatelic collections (whether or not ultra-violet UV filters are used) fading and/or damage will occur. In fact, each exposure to VISIBLE light will irreversibly and cumulatively add to any previous stamp fading or damage that has already occurred; the additive effects of exposures to such light is known as “reciprocity.” This is one of the reasons that the British Guiana looks like it does.
But, although I have illustrated that blue wool cards can be used to measure and quantify light exposure, I have not yet shown how it is that you as a collector can make use of them to protect your collections. I’ll do so in my next post.