Digital BW, The Print

Ernst,

Thanks for the informative comments.

>> ... Organic pigments are produced by chemically "stacking"
>>organic dyes to form larger particles.

>... there are no carbon particles in inkjet inks but in
>the black/grey inks.

When I first started to get into this field I made the mistake of assuming
the ink sellers knew what their products were.  I remember years ago how
impressed I was with a local photo dealer who had put a sign above the
counter with a huge "I DON'T KNOW" printed on it.  I would so much rather
hear those words than BS that causes me to waste time racing down blind
alleys.

>> Smaller pigment particles have better color, gloss and transparency but
>> worse lightfastness. (32)  [UC inks come to mind.]

>... I bet that there is something else going
>on in UC inks. First the encapsulation itself contains a colorant, whether
>that is dye or the result of a lower stacking of dye molecules.

I also have the impression that there is a colorant in the coating -- but
perhaps only of the color pigs.  (I never know how much faith to put in my
reading between the lines, however.)  I think that might be one reason the
color prints have a shorter life than the B&W prints and also, perhaps, why
the UC inks do much worse on EAM (which is not dye friendly) than do the
older Archival pigments.

>... the encapsulation ...acrylic coating

Have you seen good information that indicates the coating is acrylic?  My
recent research in coatings does seem to indicate acrylic is the best way to
go, but there are all sorts of coatings out there (and different acrylics
also).

>> Water soluble azo dyes will have a sulfonic acid group (-S03H).
>>[Imagine what that acid does when it hits an alkaline buffer.]

>Give a good bond ? ;-)

I don't know.

The EAM surface (as opposed to paper base) is actually slightly alkaline.
I've wondered if this is part of why EAM is good for pigments but not dyes.

On the other hand, when I see that the "EAM" name has only been dropped on
the rolls -- not the smaller sheets -- it makes me wonder if nothing more
than an attempt to separate markets is going on.  That common strategy would
be aimed at getting the big format guys to pay more for the high-profit
"acid free" papers Epson markets only to them.

>> Dyes will not only fade due to UV, but also due to the
>>effects of visible light.

>For the kind of work we do, the last is the main part of light fading.

I agree.  Moreover, someone who is really into his/her display prints will
probably have UV coating on south-facing windows.  Fluorescent lights in
offices (like even my little home office) may be the main UV source our
prints will have to deal with.

Even if the UV inhibitors cause improved fade tests in my fluorescent fader
(uncertain at this point), I'm not sure I want them in the acrylic coatings
I'm experimenting with.  Most of them start out more yellow (big negative to
me) and may increase the risk of negative long-term aging problems.


>> Colorant Fading
>> If a double bond is broken, the conjugation length of the molecule is
>>reduced, and the color absorption capabilities are disturbed,
>>either leading to ...fading, or leading to a shift in
>>wavelength absorption which results in a color shift.
>>The complete rupture of a bond (cleavage), ...leads to the
>>division of the molecule into two smaller ones, which
>>will each have shorter conjugation lengths. (53)
>
>> [This color shift may be part of the warming we see with most dyes and
>> pigments used in B&W printing.]

>I thought that it would fade the other way then, getting colder.
>Isn't it that the dye or other added colorant fades and the carbon
>brown becomes prominent that gives the warming ?

I think that with the dye-toned black pigments that probably is part of the
formula.  However, I see warm shifts in color pigments and pure black dyes
also.

I had originally thought that with the color pigments the color coating was
burning off -- but that was based on the, apparently, inaccurate model of a
carbon particle in the center.

>There's that older report of
>Barbara Vogt that has been mentioned on some lists before.

I summarized it some time ago on this list.

Paul
http://www.PaulRoark.com