Digital BW, The Print

Djon,

Here is another dictionary definition:-

"A distinction is usually made between a pigment, which is insoluble, and a 
dye, which is either a liquid, or is soluble. There is no well-defined 
dividing line between pigments and dyes, however, and some coloring agents 
are used as both pigments and dyes. In some cases, a pigment will be made by 
precipitating a soluble dye with a metallic salt. The resulting pigment is 
called a "lake"."

And another:-

"What is the difference between pigments and dyes?
The primary difference between these colorants is their solubility. Pigments 
used in printing inks are colorants that are insoluble in water and most 
solvents. For instance, copper phthalocyanine blue is the primary blue 
colorant used in packaging and is quite insoluble in water and organic 
solvents. As the name indicates, it is a blue pigment that includes copper. 
The rest of its structure is a highly complex aromatic structure of benzene 
rings that include nitrogen atoms.

Unlike pigments, the number of dye colorants is seemingly infinite. Dyes are 
organic colorants that are soluble, and they are commonly used in the 
textile industry and in office products, such as ink jet printers. In 
packaging applications, dyes do not have the product resistance of pigments. 
Dyes provide brilliant color and are used in products that do not require 
long-term resistance. Most have inferior solvent bleed and oxidation 
resistance."



As far as I can see, Epson is entitle to call their Ultrachrome inks 
pigment, just as many other ink firms sell 'pigment inks' as well as 'dye' 
inks (MIS, Lyson, etc).

According to Epson, the encapsulation of their pigments in a coating of a 
resin polymer is designed to prevent the pigments aggregating and settling 
out of suspension. If the polymer were to have hydrophilic groups on its 
surface (I don't know that it does), it could even be effectively 
'solubilising' the pigments.

Bob Frost.

----- Original Message ----- 
From: "Djon" <westsidemaurice@...>

 'dyes' are soluble
> and 'pigments' are insoluble.

That's true for Epson "pigments" vs the various dyes and inks in
printers, but "pigment" simply means colorant: the stuff from which
dyes and inks are made. The word is being used inaccurately by Epson,
but perhaps it's easier than explaining "encapsulation."

Ultrachrome "pigments" are different from dyes because they are
"encapsulated" and in "suspension," not "dissolved" in a "solvent". By
contrast, dyes and inks ARE in their solvent, which is usually water.
This is said to explain Epson's arguably more archival characteristic,
and it probably explains bronzing.