>>...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.
Tyler wrote:
>...In essence meaning that ink terned as carbon pigment alone does not
>necessarily indicate more longevity. We can't necessarily take that as
>insurance, there's more to it.
Yes, although in practice I find the "carbon black" in the inksets I've
tested (clearly excluding hybrid blacks with dyes in them) to be the more
lightfast than the color pigments, but with the cyan running a very close
second place.
Ernst wrote:
>...Compare the first Roland ink pigments with the pigments that were
>introduced by Generations later on etc. The Roland pigments last longer
>outdoors but their gamut is much less. C.D. Tobie called them
>prefaded :-)
I've been told at least some of the old outdoor signage printers used very
large pigment particle sizes to get great relative longevity. However,
these pigs would clog an Epson desktop printer. Also, it appears that the
smaller the particle the larger the gamut.
So, again ironically, while Epson is pursuing smaller particles and dots for
smoother, higher-gamut images, these are not necessarily what we want for
B&W longevity. We might be better off with larger particle sizes if they
would work in our printers. Realistically, however, we're stuck with the
Epson desktop printers made for the color market because B&W is not a large
enough market to support a totally different printer design.
It's interesting to consider the effects of the Epson acrylic coatings on
their particles. Does this help of hurt longevity? Does it require a
smaller pigment particle size to accommodate the acrylic coating? Acrylic
is not a particularly good oxygen barrier, so it might well be that a larger
pigment particle with no coating would be a better choice.
Note that Epson omitted the acrylic coating on the matte black and made the
particle larger. On that particle they claim to have a "solubility" layer
on the outside. What is this? Pigments are not soluble. It is probably
some treatment that increases the particle's surface area to mass.
If one could get particles to stick on glossy paper without an acrylic
coating, would the potentially larger particles allow more lightfast colors?
MIS claims its color pigments do better in lightfastness tests than UC
pigments. (I have not run a direct test of this.)
>> 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
>>"proprietary organic materials" at "5% - 10%," and "glycerols" at
>>"about 18%." Water makes up the balance.
Tyler wrote:
>Giving them the benifit of the doubt and assuming that only "carbon
>black" and "Proprietary dyes and pigments" are image forming, only
>11+% of the image is carbon black, and if "proprietrary organic
>materials" contribute any optical density, even less.
True. On the other hand, the image-forming part of the mix may be pure
carbon. I just don't know.
>>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).
>I'm curious which color inks did this. I've seen straight Ultrachrome
>B&W prints that look decent with good profiles, but would be very
>uncertain of them remaining neutral over time.
It has been consistent with all color inksets that I've tested. But, I'm
not sure if I've tested a UC grayscale print. Cone's tests indicated the UC
magenta is very good, but I suspect this could be due to the differing test
conditions. The different pigment types can have differing relative
performances under different test conditions. This includes not only
different lightfastness test, but tests relating to sensitivity to different
chemicals and even air movement. The most lightfast pigment might not be
the pigment least sensitive to atmospheric pollution.
In general, however, I think we are better off with the fewest color
pigments in our B&W prints, even if the carbon shifts yellow a bit. I think
slight warming is going to be more acceptable as a "normal" aging effect
than is a green or other non-traditional color shift.
One thing is relatively certain -- the individual color pigments will fade
and otherwise deteriorate at different rates. I'm leaning toward a B&W
toning approach that uses one (or predominantly only one) color pigment per
toner. As the color fades the prints will simply lose gamut, in effect,
slowly shifting to the carbon warm tone, but probably never totally losing
all the toning effect. I think a one-color-pigment toner minimizes the
chances of weird and potentially uneven color shifts. Right now I think all
of us are using the traditional cyan, magenta, and yellow pigments to do our
toning. I'm trying to change this.
>> 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.
>I suspect there is too much agonizing. I have many many prints made
>from the original Sundance Piezography quad inks, thought by most to
>be the devil's brew. ...
>Though a few have lightened and reddened abnormaly, the vast majority
>of them look great.
I agree. I had some old MIS original quad prints on the wall for years.
They warmed, but I didn't really even notice the warming until I held a
neutral print right next to them.
> ... atmospheric contaminants...
>This kind of thing may really be our biggest problem, many unknowns ...
Yes, and it's impossible to predict or test for most of them. Wilhelm is
now testing for ozone sensitivity, but there are so many other pollutants
that might interact with the image-forming substance, inkjet coatings, and
the paper itself.
However, the inkjet history has focused us and the market on lightfastness.
This has also been the traditional focus of many of the painting fields, for
example water colors. So, I think there is a rational reason to focus on
this issue, and it's one where, fortunately, the accelerated testing appears
to be most accepted as relevant even if imperfect.
Lightfastness is also something we can at least get to a point where,
hopefully, it will disappear as an issue in the market. I think the market
still needs to be convinced that "inkjet" does not necessarily mean that the
print will fade in a few years.
>I suspect also relevant to yellowing coatings.
Coatings, including both their yellowing and effectiveness, are still
somthing I'm pursuing. I now think solvent-based acrylics the best. The
old Rolm & Haas B72 formula is so well accepted and has been used so long
that I feel comfortable with it. It's in Lascaux Fixativ. A very similar
acrylic that has been mentioned by the chief of conservation at the National
Gallery as being essentially the same is the Grumbacher Tuffilm. He says
that these coatings have been tested out to 400 years with not problems.
They are very widely used in other fields.
PremierArt Print Shield "lacquer" is getting wide acceptance now due to the
Wilhelm tests, but I have not been able to get any information on its
coating type. "Lacquer" to me is a generic for clear coating. Many
coatings have been found to yellow over the long run. I'd be more
comfortable knowing what is in the products I use. Still, it does a good
job in the short run and has not yellowed in any of my tests. But those
tests are too short and light only. I use it, but, long term, I would have
more confidence in it if I knew it was an acrylic.
Paul
www.PaulRoark.com