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Topic: metamerism (4 msgs / 170 lines)
1) From: Kevin DuPre
If you're trying to choose a paint sample under ideal
lighting conditions, the effect called metamerism
probably holds true.  However the Agtron tiles were
meant to compare ground coffee for color match to
Agtron degree of roast by matching the color with the
[precisely manufactured] tile - pretty much
side-by-side. In that case, the optical effect
resulting from metamerism, while it may apply from an
aesthetic standpoint does not apply from a functional
standpoint.
As another example, if you took a piece of colored
fabric, of which you know nothing of the pigmentation
source, and took it to a store to buy paint that
matched, you would look at it under the lighting
conditions in the store and pick a paint that came as
close as VISUALLY possible to a match.  You could
never account for pigmentation because both are pretty
much out of your control, unless you are the fabric
and the paint manufacturer which is not likely.
You might even take the color chips home and choose
the best match under your lighting conditions at home,
but in either case you would be using your eyes and
judgement to make the selection, changing out color
chips until you had what your brain determined was a
match.
The Agtron tiles are meant to work the same way. Of
course, you could always spring for the $15,000-20,000
for an Agtron spectrophotometer and be dead on the
money, but that would put you in the realm of a
highly-repeatable commercial roaster, now wouldn't it?
:)
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--
Kevin DuPre
obxwindsurfhttp://profiles.yahoo.com/obxwindsurf"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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2) From: Dan Bollinger
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Respectfully, I disagree.  Metamerism does come into play here.  The tiles
are created using pigments, which reflect light differently depending on the
wavelength of the light being reflected.  The only way that the tiles could
operate without metamerism is if they used the same colorants in the bean,
mostly pyrolized sugar. Somehow I don't think that is the case.  ;)  Dan
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3) From: Irene and Lubos Palounek
Because the SCAA/Agtron Roast Color Classification System kit comes with two
empty petri dishes for sample preparation, I always thought that the "color
disks" that come with the kit are made using real coffee; perhaps not in
petri dishes, but made into disks.
After reading the kit description again, I realized that I am most likely
wrong. However, perhaps the color disks *are* made using the same pigments
that give roasted coffee beans their color. I just do not know.  The answer
to the question whether mesmerism does or does not apply when comparing
color of the coffee sample to the SCAA/Agtron Roast Color Classification
System's color disks depends on the pigments in roasted coffee and pigments
in the (expensive) color disks, doesn't it?
Below is the "official" SCAA description. I have not read the manual written
by Carl Staub.  Has anyone on this list have access to that manual?
As Tom, Mike, Cathy, Art and others stated, the color is NOT that important
in judging the roast; the color does not express the many factors that give
the roasted beans their aroma and taste and flavor. I fully agree. As Cathy
wrote, paint chips would probably not solve the "roast comparison" problem.
As Mike said, color IS important in some (large customer) situations. BTW,
Mike mentions Costco -- our Costco here in Austin roasts coffee in the store
and they do NOT use any color comparison; the roaster operator just pushes
"the right buttons" on the machine.
Also, I want to thank Kevin for his lengthy explanation.  I believe that we
now agree in just about everything. Just few points:
"This statement doesn't make sense - 'how can you have a "mix" of "one
frequency color"?' For example mix the lights of red and blue lasers - use
those two lasers to illuminate the same spot. Each laser produces coherent
light of a specific frequency, and those two light source mix at the target.
'If you shift that light into high amounts of red or blue, then it is true,
you will create a discernible difference. But I don't think that anybody
will be comparing Agtron color tiles under those conditions.' I disagree
here; many people think that any "normal looking" bright light is the
"correct" light for looking at colors. I know that in our home, when trying
to examine color pictures or fabrics, some people tend to go under a bright
light of a halogen table light. What a difference in colors under that light
and the OttLite!  And perhaps people like Gary would use their "favorite"
bright light. This whole discussion basically started because I strongly
disagreed with the statement that "you would be comparing the coffee AND the
color tile under the same lighting conditions. This would make the type of
lighting (unless VERY DIM) irrelevant." I strongly believe that the type of
the light source, even when very bright, and the spectrum of that light
source, are extremely relevant.
I also strongly disagree with the statements that "...the Agtron tiles were
meant to compare ground coffee for color match to Agtron degree of roast by
matching the color with the
[precisely manufactured] tile - pretty much side-by-side. In that case, the
optical effect
resulting from metamerism, while it may apply from an aesthetic standpoint
does not apply from a functional standpoint." I strongly believe that
(unless the Agtron tiles are made using the same pigments as those pigments
that give roasted coffee its color) that metamerism does apply from the
practical, functional point when using the Agtron files.
Gary wrote: "I don't know why the different lighting conditions would seem
to affect the beans
differently than the color plates in the book, but I couldn't argue with
what I saw." If you are interested, Gary, search the net for mesmerism and
read some good explanations why that is happening.
BTW, Gary, my last name is NOT Ott. I have no connection to Ott-Lites other
than a user. However, I know that light with the correct color spectrum IS
important even when the only thing you are after is the consistency of your
roasting color.
You are right, Gary, roasting is an art!
Regards, Lubos
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SCAA/Agtron Roast Color Classification System
(R4001)
Comprised of a light-weight black vinyl kit (10” x 12”x 1 3/4”) containing
eight color disks, numbered in 10% increments ranging from “Very Light”
(tile #95) to “Very Dark”(tile #25). The kit also includes 2 black
background sheets, two standard petri dishes for sample preparation, and an
easy to read manual written by Carl Staub. These eight industry standard
disks are designed to enhance consistency and assure that both roasters and
their customers are in agreement regarding degree of roast.
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4) From: Dan Bollinger
<Snip>
Definitely not.  Coffee colors come from organics and are not usually
permanent colors.  Only the inorganic colors are permanent.  Colors made
from mineral earth colors, coal tar, or anilines.
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of
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Since we are not going to be comparing color, just value (light to dark)
metamerism comes into play, but not as much as when comparing colors or
hues.  It makes sense for us to agree to compare under sunlight, an OTT
light, or any other a balanced spectrum light source.  Matching under
fluorescent or incandescent is a no-no.  Dan
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