Gum woes

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 Fri May 6 23:32:56 2005