My take is that some good reference material come very close to what Robin Myers described, as reflecting equal amounts of light across the visible spectrum. A few years ago, I purchased such a white material for dirt cheap from BabelColor. Been using it successfully in all my reproduction work ever since. But you raise a very interesting and difficult question, John, what is "white"? Is there such thing as a true, absolute "white"? Sun at midday would intuitively seem like a "natural" candidate of white, if only it could be observed directly, but at billions of candelas/m2 (I have no idea what the true value is) it's not a really good useful "candidate of white". Yet, white is so important in all color work. We speak of "white point" all the time. Photoshop has a "white point" tool. Our monitors are pegged at a certain white point and so on. White is truly everywhere, as a color. I spent many agonizing hours, days, weeks, months, years of my own time trying to naively measure "sun at midday" or what I call "direct sunlight", because I was convinced that this exact type of light could only be the "true" measure of white, since humanity has thousands of years of evolution under its belly, judging the world around us, people, animals, oceans, nature using that exact light. To me, this light is the most important "reference" for the visual system. It's abundant, it's ubiquitous and it's stable. All qualities I thought were rock-solid and immovable until I started to get some good spectra, measured by my hand, which, at first, didn't make sense. And as a true skeptic, I still have doubts about the limits of my instrumentation. Yet, many useful conclusions and interpretations could be drawn from my data and, boy!, did it make me "humble". I had no idea what absorption bands were before, yet they were there, under my eyes, oxygen, nitrogen, all kinds of atmospheric particles and whatnot. Still, despite all the technical and conceptual difficulties, I could only conclude that "direct sunlight" is indeed, for me, the "best" white out there, for reproduction purpose. If we're going to be talking about some "reference white", why not go with what nature has provided in abundance, I am convinced of? I know the idea of white is just that, an abstraction. To physically "realize" that idea, to me, only standard reference material such as Robin suggested could ever be used for that purpose. That's one part of the "recipe" of white. The other part, is the light under which this perfectly reflecting material is observed, there is no getting around that. I tend to be biased and still think of sun at midday as the best we have, regardless of all its pitfalls, that it varies during the day, how it changes relative to the position around our hemisphere, time of the year and so forth... To me, the best place to observe a fresh ColorChecker chart is still under direct sunlight, on June 21st, at noon -- see you there! / Roger Breton -----Original Message----- From: colorsync-users-bounces+graxx=videotron.ca@lists.apple.com [mailto:colorsync-users-bounces+graxx=videotron.ca@lists.apple.com] On Behalf Of John Gnaegy Sent: 9 juin 2014 16:46 To: 'colorsync-users?lists.apple.com' List Subject: is anything white? Hey list members, is anything perceived by the standard observer as technically, absolutely white? If white is all colors, and assuming that means equally, it should be illuminated by the entire visible spectrum equally and reflect the entire visible spectrum equally (or be illuminated unequally and be unequally reflective in inverse proportion). Is there a combination of light source and material like that? Snow seems like a good candidate for a material, but illuminated by what? Our sun? Stars have different spectra. Is the spectral output of our sun at midday (on the equator during an equinox, or somewhere in the tropics at the right time of year) considered the reference "white" illuminant? _______________________________________________ Do not post admin requests to the list. They will be ignored. Colorsync-users mailing list (Colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/graxx%40videotron.ca This email sent to graxx@videotron.ca