Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, " 

> If you print b&w using black inks  a n d  color inks in what mix 
> ever, there should be at least some metamerism. This seems to 
> be a physikal rule, no?

NO.

There's usually no significant metamerism with other media such as 
paintings or photographic prints, even when the colors are just 
grayscale.

Metamerism exists because the reflectance spectrum of the pigment or 
dye is PEAKY.  Imagine two red materials, A and B.   A reflects a 
gaussian distribution centered around 660 nm with an S.D. of 50 nm.
B reflects with a series of 5nm peaks centered at 660 nm every 30 nm 
apart.

Under incandescent light A and B will both look red.    Under an RGB 
triplet of LEDs, where the red LED emission peak is 660 nm they will 
look red.   But under an RGB triplet of LEDs, where the red LED 
emission peak is 680 nm A will still look red, but B will look BLACK.

(BTW it's easy and FUN to set up metamerism boxes at home and play 
with different colored objects under them.  Use a white fluorescent 
bulb in one box and an LED triplet (NOT a white LED) in the other.  
Both are peaky but in different ways so common objects (and UC 
prints) change color dramatically between them!   Also many science 
museums, such as the one here in Boston, have metamerism boxes to 
play with.)