As spring arrives and winter subsides, the likelihood of a fresh blanket of snow melts into our collective memory but just for a few minutes. Bundle up, don’t forget your scarf and let’s wander into a field of freshly fallen snow.
It’s bright out in the field, the sun is shining overhead and you really need sunglasses to look around without squinting. It’s so bright out that you can’t see any of the hills and dales around you, but once your eyes have adjusted, you can make out a few details. Still it’s all very white. You might think it’s as white as paper, but is it? How white is white?
When it comes to things like paper and fabric, how white it is can depend heavily on the amount of optical brighteners used to make it, and in the case of clothing, even how much is in your detergent.
You might be asking yourself now, “What’s in my detergent that makes my cloths look whiter; and how is that related to paper?”
Have you ever heard the phrase, “bluing for extra whiteness?” This refers to adding a bluing agent that was added to counteract the color yellow. We perceive a blue tint in things as being whiter so this was a common practice and is still used in some parts of the world.
The more modern approach is to use what are called optical brighteners. These are chemical additives that fluoresce, turning invisible ultra violet light into something the human eye can detect at the very end of the blue spectrum of visible light. This creates the same effect in a way as the bluing that was added to make a white shirt look whiter.
When this technique is applied to paper, the effect is much the same but as paper manufacturers use varying amounts of optical brighteners and some that fluoresce in different ways. What you finally see will depend greatly on the lighting you are viewing under. As some lighting has more UV in its spectrum, you are likely to see what appears to be much brighter white, and this can also create an effect of a perception of brighter colors as well.
Now let’s take out a few printed samples while standing there in that sunny, snow covered field and notice that they don’t look all that much alike, but they probably do all look whiter than the snow which lacks those optical brighteners.
We should probably end our little outing and go back inside. It’s cold and that sunlight is going to break down the brighteners in the paper and we will lose all that whiteness we like so much. The snow that will come next winter will be just as white.