Digital BW, The Print

Gary,

I frankly prefer to think of worms and lobsters as metameric than what I am 
about to say, but here goes:

Our eyes see color in ink because not all wavelengths of light are reflected 
back from the dye or pigment particle in the ink. So far so good, right? 

However you can have the sensation of a given color as a result of a 
discontinuous spectral reflection; meaning a combination of spectral "peaks" 
that arrive at your eye and get mixed together to give you a color. Alternatively 
you can have that same color (or very close to it) by a continuous "chunk" of 
spectrum.  Whether a given ink color reflects continuous or discontinuous 
spectra wouldn't matter if we always got the same sensation and saw the 
same color. But...

In order for us to see, we need light, right? Light can also be made up of a mix 
of spectral frequencies, hence, for example  we have different "color 
temperatures", as well as different color of light itself. Once again, not all light 
is made up of a smooth, continuous mix of frequencies - as the sun may be, 
for example. Fluorescent lights (especially the cheap kind) are notorious for 
discontinous spectra. 

So, when we put  inks of discontinous spectral reflections under all the 
various possible light sources (sun, incandescent, fluorescent, etc) they tend 
to react differently than inks with a continuous spectral makeup. The latter 
hold up their color better.  The ones with discontinuous spectra have a hard 
time maintaining their color:  they can't reflect back  their particular  mix of 
frequencies in the same exact proportions under all the different light sources. 
Hence their color appears to our eyes to shift. 

I am afraid this is a very abbreviated description of a subject for which you 
better look up a scientific source and not the American Heritage Dictionary! 

In practical terms, it means that some color inks exhibit metamerism because 
they don't hold up their color well in daylight and artificial sources. They may 
have been optimized for color gamut, permanence, freedom from clogs... all 
sorts of other variables, but not that particular one. It's just one more thing to 
look for when judging the performance of color inks - especially if you are 
trying to maintain neutrality across a gray scale.

I hope this helps - even a tiny bit.

Antonis





--- In DigitalBlackandWhiteThePrint@y..., "Gary Benson" <bensonga@g...> 
wrote:

...
 Ok.....well then, it goes on to define 
> metamere as: "One of a series of homologous body segments, as in 
> worms and lobsters".
> 
> Anyone got a better definition of metamerism at hand?  Maybe from a 
> complete set of the Oxford English Unabridged Dictionary 20+ 
> volumes?  American Heritage just doesn't cut the mustard.  ;-)
> 
> Gary Benson
> Eagle River, Alaska