U of S | Mailing List Archive | alt-photo-process-l | Re: Types of Gum? Dyes instead of pigments?

Re: Types of Gum? Dyes instead of pigments?

On Wed, 17 Oct 2007, Keith Gerling wrote:

oh.  thanks for pointing that out.  I wonder why that is.
Keith, I'm going to pretend you weren't being sarcastic... tho since you know so much I figured you knew the difference between pigment and dye.

At this moment I'm downstairs and my books are upstairs and having already walked enough today & assuming you know this already, I reply from memory:

Memory says the difference between what we call a dye and what we call a pigment is the size of the particle. I suppose there are other differences, but dye particles are much smaller than pigment particles, which also affects lightfastness (no pigment I have, even the most fugitive, can be made to fade as quickly as Dr. Martin's Dyes). There are some dyed fabrics that are extremely lightfast, however ... which may be due to a mordanting process, which I think is usual when dying fabric.

The dye particles, meanwhile, are so tiny they embed in the paper fiber & do not wash out. But you knew that, too. And that's why the paper doesn't clear.

Dye of course cannot embed in metal or glass, which are impermeable to ordinary water or water-based carriers. But you may even know that, as well ! Of course one could dye a gelatin or other coating applied on top of the metal or glass... I also suppose that metal and glass can be colored with other materials added or applied. ...

But that would be off-topic.


On Tue, 16 Oct 2007, Keith Gerling wrote:

As for dyes, the biggest problem I've found is that they stain.  Meaning
that if you put some on paper, it won't wash out.
Exactly. That's why they're called "dyes." They "dye" paper, but you don't
dye metal or paper so easily.




On 10/16/07, Don Sweet <don@sweetlegal.co.nz> wrote:
This chap is experimenting to see whether the plant dyes used in
are reasonably permanent.

Don Sweet

----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
To: <alt-photo-process-l@usask.ca>
Sent: Wednesday, October 17, 2007 2:40 AM
Subject: Re: Types of Gum? Dyes instead of pigments?