Re: sizing for gum tests

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
> ---------------------------------------------------------
>
Received on Tue Jan 24 10:29:07 2006