[Aquanet] stain v:s dye

[Barry D. Lindley]

A staining color is a dye.  

A substrate will not be colored by a substance unless the substance either
reacts chemically with the substrate (in which case traditionally we call it
a dye) or adheres to the mesh of the substrate (in which case we call it a
pigment). In fact, today "pigment" may be used rather loosely to include
dyes, although a pigment ought to be insoluble in water and a dye soluble.

There is no reason, in principal, that a dye cannot be lightfast, but the
chemical nature of many dyes is such that they are not.
Similarly, "pigments" may not be lightfast.  So-called "lakes" are
substances, called mordants, to which a dye may bind.  Particles of such a
pigment can then adhere to the substrate, when it would not react with the
primary dye.  Such pigments may be more easily lifted.  I am not sure, but I
believe rose madder would fall in this category.

Many classical pigments are inorganic particles or minerals, which are often
more lightfast than reactive organic molecules, and many of the early dyes
were not very lightfast.  A lot of industrial paint chemistry has resulted
in relatively light-fast dyes. Daniel Smith's Inksmith article "The study of
color"  talks some about the issue of pigment/dye development in industry.


From:
http://www.apparelsearch.com/Definitions/Dye/dye_definition.htm


"A dye can generally be described as a coloured substance that has an
affinity to the substrate to which it is being applied. The dye is usually
used as an aqueous solution and may require a  mordant to improve the
fastness of the dye on the fibre. (In contrast, a  pigment generally has no
affinity for the substrate, and is insoluble)"

And, of course, Handprint has a great discussion:
http://www.handprint.com/HP/WCL/pigmt3.html


Barry D. Lindley
Paintings and Drawings
www.BarryLindleyArt.com
 
-----Original Message-----
From: aquanet-bounces at thedigitalbraintrust.net
[mailto:aquanet-bounces at thedigitalbraintrust.net] On Behalf Of pat davis
Sent: Tuesday, September 23, 2008 1:39 PM
To: aquanet
Subject: [Aquanet] stain v:s dye

Hi, gang.

Another question or two. First, what is the difference between a 
transparent, staining pigment and a dye? Is there really one?  I keep 
hearing that dyes are not colourfast, but is it true? Second-or is it 
third or fourth... for our purposes, does it matter?

So many questions, so little time... left
Pat the Fogey

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