Black & White Gum Print Workflow
Paper: Â Rives BFK, white, 250 grams, mouldmade, 100% cotton, neutral PH, hot pressed.
Pigment:  Winsor & Newton Professional Watercolor, Lamp Black
         Winsor & Newton Designers Gouache, Lamp Black
I use Ammonium Dichromate for the sensitizer. Working with the 1:1 ratio as a starting point I use 12 âdroppersâ (as much solution of either gum or sensitizer as the stem of the dropper can hold) gum arabic to 12 âdroppersâ of sensitizer (for a total of 24 âdroppersâ) with about ½ inch to ž inch "worm" of pigment (*only about Âź inch for gouache).  Altering the ratio (even slightly, for example: less droppers of gum to sensitizer--i.e. 10 droppers of gum to 14 droppers will produce less contrast and more drops of gum to sensitizer will produce greater contrast (i.e. 14 droppers of gum to 10 drops of sensitizer). Â
Making the Print: Cyanotype
I use Cyanotype as the first layer to add detail and enhance the D-max. Â I do a 20-minute exposure (enough to achieve tone in step #3) before any gum layer is put on.
Making the Gum Print: Coating
After the Cyanotype layer, I start with a short exposure to produce tone no greater than step 2/3 to establish the shadows. Â My exposure for the first set is 1 minute 30 seconds (at a 12 droppers gum: 12 droppers sensitizer ratio). Â The seconds set is longer at 6 minutes 30/45 seconds (at a 13 droppers gum: 11 droppers sensitizer ratio) and produces tone up to step 8 to establish the mid-tones and highlights. Â For more density in the shadows, I then add a short exposure (at a 14 droppers gum: 10 droppers sensitizer ratio) for about 2 minutes (for no greater than step 3). Â Finally, to add a little "kick" to the shadow and give more depth to the print, I use lamp black gouache (at a 15 droppers gum: 9 droppers sensitizer ratio) as a final layer with a 30 second exposure time (no more than step 2).
Making the Gum Print: Development
I âstillâ develop the FIRST SET in a tray of water (about 68-75 degrees) for about 5 minutes until the boarders of the print start to clear--then in a second tray with cold water for about 10-15 minutes and change to cold water (warm water as needed) at 5-minute intervals for a total of 30 minutes development time. Â For the SECOND SET (as well as any additional sets), I still develop in a tray of water (about 68-75 degrees) for about 5 minutes until the boarders of the print start to clear then in a second tray with cold water (warm water as needed) for about 10 minutes and change water at 5 minute intervals for a total of 30 minutes development time. Â After each exposure, I also immerse the print in a tray of 1% Potassium Metabisulfite solution to keep the boarders white.
Making the Print: Workflow (exposure times may vary)
¡ Layer #1 Cyanotype â 10ml of each A/B Cyanotype chemistry. Exposed 20 minutes (enough to achieve tone in step #3).
¡ Layer #2 Gum Bichromate Lamp Black Watercolor â at 1:1 gum to sensitizer ratio (12 full eyedroppers of gum and 12 full eyedroppers of ammonium dichromate).  Expose for 1 minute 30 seconds (enough to achieve slight tone in step #3) and âstillâ developed for ½ hour in cold/warm water.
¡ Layer #3 Gum Bichromate â Lamp Black Watercolor â 13 full eyedroppers of gum and 11 full eyedroppers of ammonium dichromate.  Expose for 6 minutes 30/45 seconds (enough to achieve slight tone in step #8) and âstillâ developed for ½ hour in cold/warm water.
¡ Layer #4 Gum Bichromate â Lamp Black Watercolor â 14 full eyedroppers of gum and 10 full eyedroppers of ammonium dichromate.  Expose for 2 minutes (enough to achieve tone in step #3) and âstillâ developed for ½ hour in cold/warm water
¡ Layer #5 Gum Bichromate â Lamp Black Gouache ONLY A QUARTER INCH OF PIGMENTâ 15 full eyedroppers of gum and 9 full eyedroppers of ammonium dichromate. Expose for 30 seconds (enough to make step #2 disappear) and âstillâ developed for ½ hour in cold water.
