U of S | Mailing List Archive | alt-photo-process-l | Re: green-yellow

Re: green-yellow

Hi all,
I've been pondering over this thread for days.

When I asked a question on another forum about this a couple of years
ago, I was told that the farther the color is from violet on the
spectrum, the better it will block UV. By this logic, the UV-
blocking capability of colors should be in descending order: red,
yellow, green, cyan, blue, magenta. This makes sense theoretically,
but in practice it doesn't always seem to come out that way, in fact
the ranking of colors by blocking ability seems variable depending
more on the printer, the inkset and the light source than on the

One value and saturation for each of the primary hues doesn't tell us
much; I find Michael's HSL array much more useful in judging the
blocking characteristics of the colors at a wide range of intensities
and values. And of course Clay's approach takes even more of the
guesswork out, he's looking at actual amounts of actual inks, and
graphing their actual UV-blocking capabilities. But I don't have the
patience for that kind of detail, so I'll stick with the HSL array.
Using that array printed in the dye-based inks in my Epson 1280, I
get the following order of blocking: red, green, yellow, blue,
magenta, cyan. With my printer, cyan is the least blocking color by
far, and red the most.

It seems to me that if different printers/inksets produce different
rankings of colors by ability to block UV, then the UV-blocking
properties of a particular ink cannot be assumed to be a function of
the color of the ink.

I only do the one process, so can't compare profiles across
processes, but I've seen several examples where people have used the
HSL array for different processes, using the same light source, and
got exactly the same HSL profile for the different processes, which
suggests to me that it's the printer inks and the light source that
determine the color blocking profile, not the process.


On Apr 9, 2009, at 9:59 AM, Marek Matusz wrote:

You could walk to the chemistry department and ask one of the
chemists for a UV-VIs spectrometer. Print a patch of pure Y, C and
M and ask them to run a UV-Vis scan. This will demonstarte the
ability to absorb light at different wavelength. You will get a
curve of light absorption across the light spectrum. You would be
able to point on the curves where the maximum sensitivity of
different alt processes is, or at least what light is used for
esposure. This would be a good teaching tool for the digital
negative making. As we know from practice yellow pigment absorbs
little light in visible range but a lot in UV range.. There are
certain chemical structures that absorb very strongly in UV and
have almost no absorption in visible light. Unfortunaltely the
nature of the pigments that Epson uses for their inks and their
chemical formulas are not known.

> Date: Thu, 9 Apr 2009 10:03:11 -0600
> From: zphoto@montana.net
> Subject: Re: green-yellow
> To: alt-photo-process-l@usask.ca
> Clay,
> I have had the same issues with BW printing, though I know
nothing about the
> QTR thingy (very scientific word)(where is it, on the web?).
> A BW neg is usually magenta/yellow dots to make a red neg in my
> However, as anyone who has BW printed knows, the filter packs you
use to
> adjust contrast are yellow (low) to magenta (high). On variable
> paper responsive to these differences of filtration, grain
results. This is
> no problem for bromoil or mordancage or chromoskedasic processes
but for a
> fine BW print a graded paper is much better.
> Which is another reason I'll print my big dots this weekend in
the BW
> darkroom :).
> Chris
> __________________
> < BR>> Christina Z. Anderson
> http://christinaZanderson.com/
> __________________
> ----- Original Message -----
> From: "Clay" <wcharmon@wt.net>
> To: <alt-photo-process-l@usask.ca>
> Sent: Thursday, April 09, 2009 9:29 AM
> Subject: Re: green-yellow
> FWIW, it is very instructive to print out the QTR ink limits test
> graph the UV transmission density versus ink percentage for each ink
> on a single graph. When I did this for my printers, the 'aha' moment
> came when I realized that certain combinations of ink colors are
> to be more prone to the graininess effect that is sometimes observed
> in the highlight areas of prints. In particular, the green color
> I used for a long time combines two colors that are very far
apart in
> terms of UV transmission density at a given density: i.e. the yellow
> and cyan inks. When I constructed profiles using only ink
> that are close in terms of UV transmission density, I got some of
> smoothest highlight transitions ever.
> Clay
> On Apr 9, 2009, at 9:25 AM, Loris Medici wrote:
> > I didn't realize that the Green/Blue transparency was the
negative of the
> > Magenta/Yellow transparency. So yes, that's blue not Cyan,
thanks for the
> > clarification.
> >
> > On the other hand my question still holds -> because it was
asked in
> > terms
> > of printer inks -> not screen colors. If you see Blue on screen
> > actually printing Cyan+Magenta in the printer, so on, so on...
> >
> > S:Y->P:Y, S:M->P:M,
> > S:G->P:Y+C, S:B->P:M+C
> > (S: Screen color/P: Printer inks used to print the color on the
> >
> > When above is analyzed, it can be seen that Cyan is definitely
> > opaque
> > for UV light than Magenta is... (Magenta patch is darker than Blue
> > patch!)
> >
> > For me, 3 different printers / 3 different inksets and Yellow
was always
> > the most opaque/dense color. (Against Green and others.)
> >
> > Thanks for the long answer.
> > Regards,
> > Loris.
> >
> >
> > 9 Nisan 2009, Perşembe, 4:46 pm tarihinde, Christina Z.
Anderson yazmış:
> >> Hi Loris,
> >> The colored left of the image, the entire thing, is the
> >> printed
> >> on Pictorico (and the blue/green portion of that "negative" is
> >> inversion
> >> of the yellow/magenta). The right side of the image is a pt/pd
> >> from
> >> that negative. So yes, the pt/pd is completely all done at the
> >> time
> >> same everything.
> >>
> >> Why yellow is so dense in general and yet so pale, Mark Nelson
or Dan
> >> Burkholder could answer these questions much better than I,
but my guess
> >> is
> >> that it is because it is opposite the UV spectrum. I'll bring
my dots
> >> into
> >> the BW darkroom this weekend and get another visual in a new
> >>
> >> Why green holds back more light than pure yellow--again, Mark
Nelson or
> >> Dan
> >> Burkholder can weigh in here? My GUESS would be:
> >> 1. more actual ink of cyan and yellow is laid down to get an
even color
> >> green?
> >> 2. the green color blocks out some other wavelength?
> >> 3. the process of choice is less sensitive to a particular
> >>
> >> But one thing that may be the cause of the confusion--t he
colored dot
> >> example has pure magenta and yellow up top (magenta being
R255B0G255 and
> >> yellow being R255G255B0) which I MIGHT ASSUME (and here I am
> >> into
> >> dangerous territory) is the printer laying down magenta ink
only and
> >> yellow
> >> ink only--no mix. I ASSUME this because my printer, the 2400,
has the
> >> usual
> >> cyan, yellow, and magenta ink along with blacks. But in the
> >> green/blue part of the colored dots which is an INVERSION of
the top
> >> magenta
> >> and yellow; the blue dots are not cyan. Cyan measured on the
> >> screen is R0G255B255 but the blue dot in my example is R0G0B255.
> >> However,
> >> I
> >> do not know, unless I break apart a cyan ink cartridge and
paint with
> >> it,
> >> whether my printer is mixing inks for that color or whether it
is the
> >> pure
> >> ink out of the ink cartridge as is.
> >>
> >> Does this make sense? That there are no actual CYAN dots in this
> >> example?
> >> I'll make one, though :)
> >>
> >> I find that in the BW darkroom the yellow still holds true as
> >> dense,
> >> as my negatives are red, and the closer to the magenta end of the
> >> spectrum
> >> I
> >> go, the less light is held back. But I never use a pure yellow
> >> so
> >> there is another factor going on than the actual density of
the ink, and
> >> my
> >> first guess would be the printer driver, second the wavelength
of light
> >> in
> >> combination with the sensitivity of the particular process (bw
> >> being
> >> safe under yellow or red light).
> >>
> >> Of course, the whole basis of PDN is the response of different
> >> to
> >> different colors which is found in practice and not in theory
(if I used
> >> theory to inform my practice I'd be a dead duck--thank heavens
for those
> >> little step wedges and CDRPS and tonal palettes :). I never used
> >> blue/purple negs, for instance, until solarplate.
> >>
> >> WHEW, Loris, that was a way too long winded answer to your
> >> questions.
> >>
> >> Please weigh in, Mark and Dan??!!!
> >> Chris
> >>
> >> __________________
> >>
> >> Christina Z. Anderson
> >> http://christinaZanderson.com/
> >> __________________
> >> ----- Original Message -----
> >> From : "Loris Medici" <mail@loris.medici.name>
> >> To: <alt-photo-process-l@usask.ca>
> >> Sent: Thursday, April 09, 2009 12:03 AM
> >> Subject: green-yellow
> >>
> >>
> >>> Hi Christina,
> >>>
> >>> I was looking at your visual about colors and UV opacity (here:
> >>> http://christinaanderson.visualserver.com/Text_page.cfm?
pID=2448) and
> >>> got
> >>> confused a little bit. Are those prints from the same process
with same
> >>> working paramaters and prodecures?
> >>>
> >>> How Green (which is Yellow + Cyan) can hold back more UV than
> >>> alone, where Cyan is a poor UV blocker (slightly denser than
Magenta as
> >>> seen from your tests)? My experience with 3 different
printers taught
> >>> me
> >>> Yellow is the strongest UV blocker among color inks... How come?
> >>>
> >>> Regards,
> >>> Loris.
> >>>
> >>>
> >>
> >>
> >>
> >
> >

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