Digital BW, The Print

Martin Wesley wrote:

> I have to disagree with you on this one. Just put a drop of pigment
> ink on a piece of paper and watch it bleed out from the contact
> point. Paper is an open lattice of fibers and if the pigment
> particles are smaller that the openings in the lattice they will be
> pulled into the paper along with the liquid carrier by surface
> tension.
>
> This is what the all the coatings for inkjet papers are about, an
> attempt to control that flow of ink into and onto the paper. If the
> papers are uncoated the tiny droplets tend to bleed and you lose
> sharpness. With too much coating or a plastic coated paper and the
> ink does just sit there on top looking bad.
>
> The amount of ink penetration into the paper verses the amount
> sitting on the surface verses the amount interacting with the coating
> determines the many different characteristics and appearances of all
> these papers.

Paper coating is a *very* complex issue.  My source of information here, about the coatings is:  "Stability
Issues and Test Methods for Ink Jet Materials", by, Barbara Vogt, Department of Image Engineering, University
of Applied Science, Cologne

The web address where you can download the PDF is:
http://www.geocities.com/mortenryhl/index.html

It is a *very* long document (42 pages), and I have not finished reading it.  However, in this document the
chapter on 'coating' speaks to just this subject. The whole point of pigment ink is to not actually be
absorbed by the paper.  If it were to go into the paper, there would be a loss of apparent sharpness.  And
people on this list have shown this to be true.

Your test method: "Just put a drop of pigment ink on a piece of paper and watch it bleed out from the contact
point.", I think is faulty.  By applying so much ink (an actual whole drop, as compared to a 6 picoliter
droplet) you are overwhelming the coating on the paper.  These paper coatings are designed to accept the ink,
and essentially have it dry, as soon as it is laid down.  They are also designed not to swell (like a gelatin
coating), and not to crack.

So again, I maintain (in an ideal situation) the ink hits the surface of the substrate, it never reaches the
actual paper, but sits on top of the paper, inside the coating, which is *very* thin.  Thin enough to still be
considered 'sitting on the surface'.  Using dye based inks is different than pigment inks.

Hopefully, someone else on this list, with more real knowledge of the science involved here can explain it
better.

Harvey Ferdschneider
partner, SKID Photography, NYC



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