Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!houxz!vax135!cornell!uw-beaver!tektronix!hplabs!sri-unix!Gloger.es@XEROX.ARPA From: Gloger.es@XEROX.ARPA Newsgroups: net.physics Subject: Re: What polishing does to the surface of rocks. Message-ID: <443@sri-arpa.UUCP> Date: Thu, 26-Jul-84 05:26:00 EDT Article-I.D.: sri-arpa.443 Posted: Thu Jul 26 05:26:00 1984 Date-Received: Sat, 28-Jul-84 10:24:49 EDT Lines: 37 Besides your rocks, notice that ice is almost colorless, but when shaved or crushed it turns milky white. I think what you're seeing must be that highly irregular surfaces reflect almost all colors of light in random directions directly from the surface, so that they appear white. This goes for objects of any color, from black to white to colorless transparent. To the extent the object material is transparent, it appears white as either its external surface or its internal structural faults are randomly reflective. If you take an object with an irregular surface and polish it, you're then able to see past the previously apparently white surface to the true color of the material, or, to the extent the object is transparent, you can then see past the white surface to the interior. If you take any material and reduce it to fine dust, it will tend to look white. (Have you ever seen flaming red dust?) So what color is the moon really? It looks off-white, but if you could polish a dust particle of the type which constitutes its surface, might it be green? By the way, is a yellow rose yellow? That is, does a yellow rose appear yellow because it reflects yellow light and absorbs other frequencies? Or does it not reflect yellow after all, does it perhaps instead reflect red and green which combination the eye senses as yellow? More generally, for objects in nature which appear in colors other than primary light colors, what number and kinds of objects actually reflect their apparent color in a single frequency band, which reflect multiple other colors that the eye combines to the apparent color, which do both? (I suppose I should go play like Isaac Newton with a prism. Short of that, there are presumably clues to be had from observing how many objects exist with apparent colors not contained in the rainbow spectrum, and thus their colors necessarily composed of multiple others - or are there such out-of-the-rainbow colors?) Paul Gloger