Re: Gum woes

From: Joe Smigiel ^lt;[email protected]>
Date: 05/07/05-06:42:27 AM Z
Message-id: <s27c7f86.015@gwgate.kvcc.edu>

Scott,

What exactly did you find problematic? It sounds like you are reporting
a problem with how the emulsion coated. Is that all?

Your first emulsion mix sounds too dilute to me and might be the cause
of staining which I'm interpreting your reference to "grained up" to be.
 The processed prints came out speckled with pigment, right?

The second emulsion sounds too thick to me and hence hard to spread
evenly. OTOH, the oil-like spots could be sizing inconsistencies within
or on the paper.

Try an emulsion closer to 1 part gum+pigment mix to 1 part dichromate.
(Eliminate the water from the first mix and use more dichromate in the
second.) You might also find saturated potassium dichromate might
behave better than ammonium (but I'm sure others will take issue with
that statement so YMMV.)

Can you post an example somewhere online for us to look at?

Joe

>>> swphoto@verizon.net 05/07/05 1:32 AM >>>
Hi all:

For the first time since my "Introductory Alt Process" course at the
University of Maryland I began to take a serious interest in gum
printing and have some problems/questions that I hope the list can help
with. I drew most of my information on gum printing from Scopick's Gum
Bichromate Book, Christopher James' Alt Process book, Katharine Thayer's
website, and Sam Wang's Unblinking Eye article.

To start, I jumped right in with 3-color printing. My process was as
follows:

     Making inkjet separation negatives from my RAW files:

        1. Adjust exposure, color, shadows, and open image in 16 bit at
17x25 @ 240dpi.
        2. Select RGB color channels one at a time and convert to
grayscale.
        3. Invert image.
        4. Set size to 5x7 at 300dpi.
        5. Print on Westjet transparency using an Epson 1280 with
pigmented inks.

According to Scopick's book, printing from separation negatives I was to
use a complementary color for each separation I made

so I used the following:

     Separation Complementary Color Color Used

     Blue Yellow Winsor & Newton
Artist Watercolor
                                                              Lemon
Yellow

     Green Magenta Winsor & Newton
Artist Watercolor
                                                              French
Ultramarine/Cadmium Red Deep
                                                                 (mixed
1+1)

     Red Cyan Winsor & Newton
Artist Watercolor
                                                             French
Ultramarine/Permanent Sap Green
                                                                (mixed
1+1)

     (all pigments mixed at 1gm of pigment to 3 ml of Winsor & Newton
Gum Arabic)

Each separation negative was printed on 4 sheets of paper for different
times. The paper was Daniel Smith Lenox; preshrunk, gelatin sized, and
hardened with chrome alum about a month ago. I mixed the sensitizer
using James' "5-10-10" formula for a texturally smooth coating:

     10 ml gum arabic / pigment (see above)
     10 ml distilled water
      5 ml ammonium dichromate, 25% solution

Each sheet was processed as follows:

     First coat: Yellow
          Emulsion: brushed on with a hake brush and smoothed until just
tacky.
          Dry Time: 30 minutes by cool air fan in dark.
          Exposure:
               Sheet 1: 1.5 minutes
               Sheet 2: 3 minutes
               Sheet 3: 6 minutes
               Sheet 4: 12 minutes
          Development: 3 still water baths for 30 minutes, 20 minutes,
10 minutes.
          Dry Time: 30 minutes by cool air fan in dark

     Second Coat: Magenta
          Emulsion: brushed on with a hake brush and smoothed until just
tacky.
          Dry Time: 30 minutes by cool air fan in dark.
          Exposure:
               Sheet 1: 1.5 minutes
               Sheet 2: 3 minutes
               Sheet 3: 6 minutes
               Sheet 4: 12 minutes
          Development: 3 still water baths for 30 minutes, 20 minutes,
10 minutes.
          Dry Time: 30 minutes by cool air fan in dark.

    Third Coat: Cyan
          Emulsion: brushed on with a hake brush and smoothed until just
tacky.
          Dry Time: 30 minutes by cool air fan in dark.
          Exposure:
               Sheet 1: 1.5 minutes
               Sheet 2: 3 minutes
               Sheet 3: 6 minutes
               Sheet 4: 12 minutes
          Development: 3 still water baths for 30 minutes, 20 minutes,
10 minutes.
          Dry Time: 30 minutes by cool air fan in dark.

What I noticed was that the sheet exposed for 3 minutes for each color
was the "best". I found that the yellow coat went down very smoothly and
had a "creamy" texture. The magenta and cyan coats were much harder to
get smooth and "grained up" - almost like the look of a 35mm infrared
negative enlarged to 20x24.

I tried printing the same as above but changed the sensitizer to James'
"Traditional Formula":

     9 ml gum arabic / pigment (as above)
     3 ml ammonium dichromate, 25% solution

The coats were very hard to apply and get smooth. All seemed to "bead"
and "grain up" like there were spots of oil on the paper and "pulled" in
areas like the gelatin sizing was not hardened and was coming up and
mixing with the sensitizer.

I tried printing the negatives again this time using both sensitizers
and pure tube colors (no mixing colors):

     Separation Color Used

     Blue Winsor & Newton Artist Watercolor
                          French Ultramarine

     Green Winsor & Newton Artist Watercolor
                         Permanent Sap Green

     Red Winsor & Newton Artist Watercolor
                         Cadmium Red Deep

     (all pigments mixed at 1gm of pigment to 3 ml of Winsor & Newton
Gum Arabic)

Again I ran into the same problems as before; almost exactly. Could it
be the paper, the sizing, the pigments, the sensitizer formulas; or a
combination? Any help would be appreciated.

TIA, Scott

Swphoto@verizon.net

PS:

Looking through my collection of paints, I found the ones listed below
and wondered if anyone could shed some light on which ones to use.

Winsor & Newton Designer Gouache
     Alizarin Crimson Permanence B Series 1
     Permanent Green Deep Permanence B Series 2
     Burnt Umber Permanence AA Series 1
     Lemon Yellow Permanence A Series 1
     Phthalo Blue Permanence A Series 1
     Ivory Black Permanence AA Series 1

Winsor & Newton Artist Watercolors
     Cadmium Red Deep PR108
     French Ultramarine PB29
     Permanent Sap Green PG36/PY110

Grumbacher Academy Watercolors
     Ultramarine Blue PB29
     Prussian Blue PB27
     Lamp Black PBk6
     Thalo Red PV19
     Grumbacher Red PR170/Pr188
     Lemon Yellow PY3
     Cadmium Yellow Medium Hue PY3/PY65
     Sap Green N/A
     Hooker's Green Deep Hue PG36/PB15:4/PY97/PY65?PBk6
     Chromium Oxide Green PG17
     Burnt Umber PBr7
     Raw Umber Hue PBr27/PBr7/PY42
     Van Dyck Brown PBr7/PBk6
Received on Sat May 7 06:39:04 2005

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