Digital BW, The Print

Tyler Boley wrote:

>--- ... "ccolbertbw" <ccolbert@u...> wrote:
>> I find it hard to believe that "mixing" the colors in the 
>>bottle requires so much less color pigment than separately applied 
>>dots that it has a differential effect on longevity...

>Let me add to the confusion. There was information some time ago,
>possibly from John Nollendorfs, that two inks mixed in solution and
>printed vrs the same two colors mixed "on paper" as separate dots,
>would in fact have different longevity. My suspicion is that those
>results would be different for different kinds of inks and nothing
>definitive can be concluded about all ink mixed as such.

I've assumed that mixing in the bottle v. on the paper makes little
difference, but I have not done a well-controlled test of this.  The
pigments would have to be the same, because the quality of same-color and
same-type pigments do vary.

Also, the base that is used might affect the outcome.  I have been notably
unsuccessful at using the Epson Archival color pigments in mixes.  (They
fade.)  I suspect the bases I have available damage the pigs. 

>There is a pure carbon quad set, the Piezography Carbon Sepia set.

I have tried also to keep the option of an essentially pure carbon print
possible with the Ultra Tone inksets.   It is true that minute amounts of
the toners end up in the deep shadows as needed to turn on the black ink,
but I'd guess it is so little that the effects on longevity would be nil.

>Bill Bergh had it specifically made with no color pigments. Cone's own
>published RIT fade tests show that, much to everyone's suprise, the
>tinted sets lasted longer.

These test results do make me wonder about the quality or completeness of
the information we are getting.  It may be, however, that the Cone sepia
really is "un-toned carbon," but that it is milled to particle sizes that
are so small they fade faster.  Ironically, the smaller the particle, the
larger the surface area to volume ratio is.  This larger
surface-area-to-volume causes faster oxidation, which is the cause of most
fading.

All my information indicates that carbon, on average and all else being
equal, is more stable that the color pigments now being used to tone it.
The Wilhelm tests are the most authoritative that are very consistent with
this.  (Carbon does yellow, however, and virtually everything fades.)

>... we have NO idea what's in anything we buy to an exact degree. 
>Even if I naiveley thought these people were in 100% disclosure, 
>I don't think even they know everything, they don't make the stuff, 
>only contract it.  Who knows exactly what's in the Septone and Eboni ...

So true.  I've been trying to learn more about pigments in general, and I'm
at the point where I doubt even the suppliers to those from whom we buy know
a lot about the chemistry of the pigments.

My brother's chemistry Ph.D. thesis was on carbon and he worked in that
field for years.  Even he is reluctant to speculate as to what is in the
"carbon" inks.  He guesses the core is graphite.  In graphite the carbon
molecules form plates (thus the lubricating quality).  The plates are rather
inert except at the edges.  There is apparently an entire sub-specialty of
chemistry that deals with these carbon edge effects.  

The large chemical companies (which I assume are the ultimate sources of
these pigments) are very unlikely to tell us or anyone else their trade
secrets.

Note that the Epson MSDS's make it appear that their black pigments are not
only carbon -- maybe not even predominantly carbon.  For example, the Epson
Light Black MSDS lists "carbon black" as < 1%."  "Proprietary dyes and
pigments" are "< 8%."  Then, of course, there are "proprietrary organic
materials" at "5% - 10%," and "glycerols" at "about 18%."  Water makes up
the balance.

I especially wonder what the "proprietary dyes and pigments" are.

I have tested the Epson UC and MIS UC clone blacks and light blacks against
each other, and they are very similar in the fade results I get.  I consider
them equal. 

The color-based grayscale patches I've tested tend to fade faster and shift
green (indicating a relatively weak magenta -- which is consistent with my
general pigment reading).  

The "carbon" only gray patches shift yellow -- but with a yellow channel
reading that is actually increasing in density.  That is, it's not "fading"
as such.  I could offset this with some yellow dye that would fade (the key
to my original FS-N "non-warming" inkset).  However, not only as a matter of
principal, but also due to Eboni's sensitivity to dyes on the parking pad, I
don't want to put any dyes into the mix.

My information suggests that the color pigments used in inkjet printing are
also organic (carbon-based).  (However, this does not mean that they will
not fade faster than carbon black.)  

>...Only specific conclusions from specific tests is really meaningful.

And even there one has to be careful about the test conditions and the
biases of the tester.

I, obviously, decided I had to do my own testing to get a handle on what was
going on.  I know they are not perfect, but all things considered, I intend
to rely mostly on my own testing and what Wilhelm reports.  (Yes, I trust
him more than some.) 

While we might agonize the details, the bottom line is that our
predominantly carbon (my best guess) pigments on buffered cotton paper are
very lightfast and archival (in dark storage).  The higher the percentage of
"carbon black" the more lightfast they appear to be.  (And I'm trying to
find toning pigments that make this caveat moot.)

Paul
www.PaulRoark.com