Gum Bichromate Workflow 2012 ©

MAKING THE NEGATIVE:

Image↵Mode↵8 Bits/Channel 

Image↵Auto Color

Image↵Adjustments↵Color Balance↵-35 Cyan

Image↵Adjustments↵Hue/Saturation↵+30 Saturation

Image↵Mode↵Multichannel

Split Channel

Image↵Adjustments↵Invert

Image↵Adjustments↵Levels↵Auto

Image↵Adjustments↵Curves

Apply Curve:

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MAKING THE PRINT:

Using the Cyan negative, I start with two layers of Cyanotype (old Cyanotype formula with 1% Ammonium Dichromate solution for added contrast—6 dropper stems per 20ml of liquid, 10ml A + 10ml B).  I expose enough to achieve slight tone in step 3.

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Starting with the Magenta negative I mix equal parts of Ammonium Dichromate sensitizer with Gum Arabic (12 dropper stems of each) and about and inch of pigment (Schmincke Pthalo Blue for the cyan, Permanent Carmine for the magenta and Cadmium Yellow Middle for the Yellow).

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SET 1:  I expose and develop enough to achieve slight tone in step 3 and repeat with the Yellow and Cyan negatives.

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SET 2:  I then increase the Gum to Sensitizer ratio to 13:11 (for greater contrast) and expose and develop the three layers long enough to achieve slight tone in step 8.

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SET 3:  I increase the Gum to Sensitizer ratio again to 14:10 and expose and develop the three layers long enough to achieve slight tone in step 3.

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Using the same 14:10 ratio and the Cyan negative I do a short exposure (about 30 seconds) with Lamp Black.

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Gum Bichromate Journal: Tweaking the Shadow Curve (part 2)

Although I liked the shadow density in my last print, I felt it may have been getting too dark and losing some detail.  So, I changed the curve slightly to bring the numbers up in the first four steps. The new output numbers below appear in red below with the new curve to the left.

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Here is the result:

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I like the depth of shadows, quality of description and overall contrast of the print.

Here’s a side by side comparison of the print from the 2011 curve on the left and the new print on the right with the corresponding curves below.

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One final test will see if this will be the new 2012 curve:

Input              Output

0——————–21

16——————49

30——————63

44——————71

58——————76

72——————80

86——————83

100—————-85

The Gum Bichromate Journal: YMC NEGATIVES WORKFLOW

1.            Start with an image smaller than the media size

2.            Open document with the Channels window open

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3.            Image‐Mode‐Multichannel

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4.            Automatically the RGB layers become CMY layers

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5.            Click on the icon to the right of CHANNELS

6.            Split Channels

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7.      Automatically the three CMY layers become three distinct B&W images

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8.            Starting with the Yellow layer-Image-Adjustment-Invert

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9.            Image-Adjustment-Levels

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10.            Auto

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11.            Image Adjustment-Curves

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12.            Load Preset

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13.            Select-All

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14.            Edit‐Copy

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15.      Edit-Paste (this will create a new layer that you can delete later on)

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16.            Select the Background layer-Edit‐Fill

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17.            Black-100%

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18.            Image‐Canvas size

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19.            Canvas size to equal media size-Canvas extension color-Black

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20.            Drag YMC step tablet

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21.            Position YMC step tablet

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22.            Drag four registration marks

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23.            Position registration marks

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24.            Drag Y step tablet

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25.            Position Y step tablet next to the YMC step tablet

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26.            File‐Save As‐Yellow

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27.            Repeat steps 8‐12with the Magenta layer

28.            Drag Magenta layer

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29. Change opacity of the Magenta layer to 50% to see the Yellow layer beneath

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30.            Enlarge to see individual pixels

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31.            Position Magenta over the Yellow layer

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32.            Delete Yellow layer

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33.            Change opacity of Magenta layer back to 100%

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34.            Drag M step tablet

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35.            Position M step tablet next to the Y step tablet

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36.            Delete the Y step tablet

37.            Save As-Magenta

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38.            Repeat steps 28-36 with the Cyan layer

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39.            Save As‐Cyan

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