Chris,
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.
Marek
> 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 practice.
> However, as anyone who has BW printed knows, the filter packs you use to
> adjust contrast are yellow (low) to magenta (high). On variable contrast
> 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 and
> 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 going
> to be more prone to the graininess effect that is sometimes observed
> in the highlight areas of prints. In particular, the green color that
> 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 combinations
> that are close in terms of UV transmission density, I got some of the
> 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 you're
> > 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 screen)
> >
> > When above is analyzed, it can be seen that Cyan is
definitely more
> > 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 "negative"
> >> printed
> >> on Pictorico (and the blue/green portion of that "negative" is the
> >> inversion
> >> of the yellow/magenta). The right side of the image is a pt/pd print
> >> from
> >> that negative. So yes, the pt/pd is completely all done at the same
> >> 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 process.
> >>
> >> 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 wavelength?
> >>
> >> 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 getting
> >> 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 bottom
> >> 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 computer
> >> 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 being
> >> 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 negative
> >> 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 paper
> >> being
> >> safe under yellow or red light).
> >>
> >> Of course, the whole basis of PDN is the response of different processes
> >> 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 succinct
> >> 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 Yellow
> >>> 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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