Re: sizing for gum tests

Stonehenge White

Gord

On Tue, 24 Jan 2006, Katharine Thayer wrote:

> Great stuff. What paper are you using, Gord?
> Katharine
>
>
> On Jan 24, 2006, at 8:19 AM, Gordon J. Holtslander wrote:
>
> > Hi:
> >
> > I continue playing around with sizing techniques for gum.
> >
> > I haven't been happy with tray sizing - my results have been
> > inconsistent
> > so I've been playing with brush sizing - actually roller sizing.
> >
> > I've been applying the size with a foam roller with a fine nap finish.
> > The roller leaves small bubbles, so I finish the size with a paint
> > pad - a
> > 7 inch wide pad. The pad has a fine layer of bristles on a 1/4 thick
> > piece of foam. Produces a nice even coat.
> >
> > I use chrome alum as a hardener and add it to make a concentration
> > of 0.5%
> > of the size mixture.
> >
> > I decided to be more scientific and introduce only one variable at
> > a time.
> >
> > I tried three sizes techniques, single coat gelatin, double coat
> > gelatin
> > and single coat casein. Gelatin was mixed one envelope of plain
> > knox food
> > grade in 250 ml water, left to sit for 1/2 hour heated to 50 C and
> > then
> > add chrome alum.
> >
> > The casien - I put 30 g of scientific grade powdered casein in 300 ml
> > water, add 100 ml ammonia (household grade), and chrome alum (at 0.5%)
> >
> > Double coat gelatin - I applied gelatin, let it dry for an hour, and
> > applied another layer. Single coat gelatin and caesin - applied a
> > single
> > layer and dried.
> >
> > I coated one small sheet of each with the same gum/dichromate/
> > pigment mix.
> > Exposed to a test negative and a stouffer 21 step tablet, at the same
> > exposure time.
> >
> > The double coated gelatin gave the best results, clear highlights and
> > prints 9 distinct steps on a stouffer 21 step tablet
> >
> > single coat gelatin produced mottled highlights. The gradation
> > between
> > the steps was very different compared to the double coat gelatin. The
> > difference between the steps is not pronounced. The single coat
> > gelatin
> > size produces a much more contrasty image. Almost no detail in the
> > darker
> > regions compared to the double coat gelatin. Hard to see a
> > differnce in
> > the steps. Prints a very short tonal range.
> >
> > The single coat casein size, produced results very similar to
> > single coat
> > gelatin, but it produced a denser black, and somewhat more detail
> > in the
> > highlights, but still had mottled highlights. Contrast appears to be
> > better than single coat gelatin, but not as good as double coat
> > gelatin.
> > Looks like casein sizing might support an image with a longer tonal
> > scale.
> >
> >
> > Will try a double coat casein size and see how it compares to
> > double coat
> > gelatin size.
> >
> > Gord
> >
> > ---------------------------------------------------------
> > Gordon J. Holtslander Dept. of Biology
> > holtsg@duke.usask.ca 112 Science Place
> > http://duke.usask.ca/~holtsg University of Saskatchewan
> > Tel (306) 966-4433 Saskatoon, Saskatchewan
> > Fax (306) 966-4461 Canada S7N 5E2
> > ---------------------------------------------------------
> >
>

---------------------------------------------------------
Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
---------------------------------------------------------
Received on Tue Jan 24 10:43:05 2006