Digital BW, The Print

Igor,

>I always thought the UT-FS was pure carbon...

No, it's a blend.  Carbon by itself is warm -- about half way to a sepia
tone.

>However, I did notice that my prints, on photo rag, get a lot warmer
>after some weeks or months, and there is some change in the density
>too. Even under very moderate and incidental artificial light. The
>fresh print looks stunning, but after a while it gets too red.

That surprises me.  The UT-FS inkset is about as archival and lightfast as
any.  In fact, the UT family is the most lightfast set of inks, overall,
that I've ever tested.

There is some warming that is normal with carbon inksets.  This has more to
do with carbon itself warming up.  It's not that much, however. 

With the original FSN I tried to avoid this by using a counter-warming
strategy that put some yellow dye into the mix.  This faded, shifting the
tone cool and offsetting the warming of the print.  However, with the UT
family of inks I decided not to use this approach both because I want no
dyes in the inks and the shift was within what I thought would be an
acceptable range.

I do not, however, usually us Photo Rag.  It makes me wonder if that paper
and perhaps the environment have something to do with the tone shifts.
Although I expect a slight warm shift from the carbon, most of the effects I
see from light are the burning out of the optical brighteners in the paper.
I avoid these.  When the exposure to light is enough to start fading the
pigments, the R 800 Blue is the first to go, which would shift the tone
warmer and greener.  The cyan is rather tough, but it can be faded via gas
attack.

>And is there such a thing as pure carbon ink?

Yes, the UT-R2-Warm is pure carbon.  Most of the variable-tone inksets have
a carbon channel and can print pure carbon with the right curves or
profiles.  Pure carbon will also warm a bit with age.  At first, the density
might actually increase, especially at the 100% black point.  You could also
do "black only" printing with Eboni and have a "pure carbon" image.  (There
are always non-image forming substances in the inks, but I do not find
visual affects from them to be significant.)

I wish we had totally lightfast pigments, but such do not exist.  One
independent tester rated the early UT2 inks, with a UV coating, at over 600
years of display.  That's about as good as it gets.  Even silver prints
deteriorate.  But, frankly, I suspect the warming you're seeing is not
fading from light, but some other effect.

Paul
www.PaulRoark.com