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[Phys-L] Re: Color (was LED mini-flashlight price break)



I have examined John Denker's page at
http://www.av8n.com/imaging/dye-spectra.htm after Bernard Cleyet
contributed some spectra. I have also read Larry Woolf's response.

Although there is no doubt that John is correct that yellow food
coloring at high enough concentration yields orange and eventually red,
I prefer to look at the situation as Larry described it. That is, we
need to view subtractive mixing as starting with 100%R, 100%G, and 100%B
and then subtracting R (using cyan dye) and subtracting G (using magenta
dye) and subtracting B (using yellow dye). Viewed this way, you don't
use any of the subtractive primary dyes beyond the point that their
respective complementary additive primaries have been fully subtracted.
For example, if you are using a cyan dye, you can make it stronger and
keep subtracting red until the red is all gone. At that point you do
not increase the cyan dye any further; or if you do, you are not doing
traditional subtractive mixing any more.

Therefore, I believe it is not correct to say (within the context of
subtractive mixing) that yellow plus yellow yields orange. Yellow plus
yellow yields yellow until the point there is no blue left to subtract.
At that point you either quit adding yellow, or realize you are not
doing traditional subtractive mixing.

I have also recorded the spectra of some dyes using an Ocean Optics
spectrometer. One set of spectra are those for McCormick yellow food
color at various concentrations. I have incorporated these spectra into
a 3-page document that you can access as an Acrobat file from by
website. I am hoping this document clearly explains what I feel is a
good way to view real dyes used as subtractive primaries. Here is the
reference...

http://www.bluffton.edu/~edmistonm/YellowDye.pdf

I have also recorded the spectra of the CYMcm dyes I use in my Epson
1280 printer on which I do my digital photogrpahy. I have a continous
inking system from Media Street (no more buying ink cartridges) and I
ran spectra of the Media Street dyes at various concentrations and
various combinations. The results are wonderful... just what you would
expect from high-quality dyes used for subtractive mixing in a
high-quality printer. I am working on a document to show these. Alas,
I have already exceeded the time I can spend on this for this weekend,
and I now have to grade some lab reports. You will have to wait a bit
for the wonderful results I have from playing with Media Street printer
inks.

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu