Re: Help with gum pritns on black paper with white Gouache.

Dave Soemarko wrote:
>
> > BTW, I did used to print with gouache, as there were some **gorgeous**
> > hot pink, purple, and orange colors I liked. Then someone questioned
> > their archivalness so I quit.
> > Chris
>
> Chris, the question about gouache's archivalness is probably due to some
> readings in old materials. Gouache used to be cheap poster colors with
> fugitive pigments or dyes and white added (for opacity). Nowadays if you buy
> artist gouache (for example, Winsor and Newton), they are basically the same
> as watercolor except that the concentration is higher for opacity reason.
>
> And for the same reason, gouache can be used for gum printing for opague or
> transparent look. It all depends on how much you use.
>

I haven't seen the post that this refers back to, but I'll just chime in
with a ditto for what Dave says about archivality of gouache. The cheap
designer's colors, sometimes called gouache, are mostly made with
fugitive pigments and are notoriously fugitive. But the lack of
archivality is a function of the pigment, not of the fact that it's
gouache. It's the same with artist's watercolor paints vs artist lines
of gouaches: the paint is as archival as the pigment it contains.
Alizarin crimson in watercolor is fugitive, as is alizarin crimson in
gouache. But phtalo is as permanent in gouache as it is in watercolor
paint.

But I would disagree with the statement that artist's gouaches are just
more concentrated versions of watercolor paint. Gouaches are
specifically formulated to be opaque. It's true they do tend to use
more pigment, and to mill the pigment differently, but they also change
other ingredients to render the paint more opaque. The cheap designer
colors render the paint opaque by adding white chalk to the paint; the
better artist lines render the paint opaque by the way the pigment is
milled and by the manipulation of other ingredients to change the way
the light reflects off the surface of the paint. I used to think that
all gouache had some white added, but I later learned that this is true
only of the cheaper gouaches. The way the manufacture of the better
gouaches was described to me (by Arthur Graham of M. Graham paint) the
resulting paint bounces the light rays around on the surface of the
paint rather than transmitting it through the paint and reflecting it
back to the eye the way it would happen with transparent watercolor, and
the scattering of the light rays at the surface is what gives it the
matte or opaque-like effect.

No matter how concentrated you make a transparent pigment, it will
always be transparent, because that's the inherent nature of the
pigment.( The analogy I use on my website to help people see the
difference between transparent and opaque pigments is to think of the
difference between agates and shale. You can see through an agate even
though the material is very hard and solid. But you can't see through a
piece of shale, because it's opaque, not transparent.) So to make a
gouache, which is intended to be opaque, using a transparent pigment,
you would have to render it opaque somehow, either by adding chalk to
it, as they do with cheap gouaches, or by milling it differently and
adding different ingredients to change the way the light reflects from
it, as is done by the makers of the better lines of gouache.

Whether you can get the same effect with either transparent watercolor
or opaque depending on how much you use, I would also disagree with
somewhat. I think it probably depends on the gouache, but I'm told that
if you dilute some artist line gouaches down enough, they will behave
like transparent watercolor and give a transparent effect that you
wouldn't be able to distinguish from a transparent watercolor of the
same color. I was told by Arthur Graham that this is true of the M.
Graham gouaches. I hate to disagree with someone who obviously knows his
own paints, but I think that's probably only true when painting on white
paper, that you can't tell the difference between them. Over a dark
background, if you compare a transparent light-valued pigment in
watercolor paint to the same pigment in gouache, even at a very low
concentration the gouache pigment will be visible as a light veil of
color over the dark background, whereas the same transparent pigment in
transparent watercolor will disappear against the dark background.

Gotta go, more on this later,
Katharine
Received on Tue Jan 18 14:23:25 2005