Think the colour transmitted is the remainder after the attenuation of the other colours. Hence if a liqid absorbs red and blue light it looks green to tranmotted light. If it absorbes green light it looks magenta to transmitted light. The absorbtion process is where electrons in the molecule or transision metal that is present is promoted to a higher level ans only accepts photons of the correct frequency. Compounds with conjugated dienes (-C=C-C=-C=C-...) have a band over the which they absorb light. The promoted electron will usually fall back and re-emit another photon at the same frequency but it will be in all directions so the intensity in the bean direction is reduced. In some cases the electron drops to a midway level with the emmission of a photon of lower frequency (longer wavelength) and stay there for a while. Over a period of time (the half-life of the state) half the electrons will drop from this midway level to the ground state and emit another low energy photon. This is called flourescence, where the half life is long (several hours) then the object will glow for a long period. Phosorescence is where slow burning causes a glow without heat. Chemical luminescens is where a chemical change leaves molecules in a high energy state which decays with the emmission of a photon or photons. Please excuse my spelling. Chris http://www.chris-image.co.uk http://www.chrisscrazyideas.co.uk http://www.chrisssoftwareshop.co.uk -----Original Message----- From: owner-photoforum@listserver.isc.rit.edu [mailto:owner-photoforum@listserver.isc.rit.edu]On Behalf Of Gregory Fraser Sent: 19 June 2002 14:44 To: List for Photo/Imaging Educators - Professionals - Students Subject: RE: "Magical thinking" Hey Karl, Since you are a chemist (and who knows what else) perhaps you can answer two questions for me. 1. I believe I read somewhere that transparent but colored objects appear to be the color they are because photons of light strike their atoms and excite the electrons which then emit energy as they drop back down to their natural state and the frequency of this energy dictates the color that we see. (more or less. I know the human eye and mind as well as the atmospher do influence our perception.) Did I understand this correctly? I believe I just solved question 2 myself. It took so long to type out and to word clearly that I figured it out just by concentrating on it. I have wondered for a long time why when crystals form (say in a geode) they form a somewhat random mass (like snow) out of which shafts grow. I didn't know how the crystal knew to change their growth pattern from the snow shape to shaft shape. What I think happens is the crystals form all around the interior of the geode simultaneously and grow until they hit another crystal. This forms the random snow but some of the crystals do not hit others and therefore continue to grow in the shaft shape. Well anyway, what about the question 1? Ever heard of that theory before? Greg
