For now the discussion will be on gum printing, continuing from earlier posts. Where I left off was after treating the paper and formulating a sensitizer/binder relationship. As I pointed out earlier, controlling the image stability on the paper, while at the same time also controlling the amount of pigment the gum solution can hold without staining the paper, is a hand shake between the two. Each is an dependent variable, meaning it is a variable, but also having influence on the other variable.
The two gum prints posted have two entirely different looks, one looking something akin to a Pastel and the other much smoother continuous tone, with transparent color depth and some texture and detail. That had to do with this handshake. I reformulated the chalky one and ended up with the smooth one. At the time of this printing, looking up information meant a trip to a local library in hopes the librarian there had even a scant interest in historical photographic processes. What I found was "The Keepers of Light", my first foray into the world of coating your own paper techniques. Being I had already been contact printing with paper negatives this seemed like a win-win situation.
The pastel looking gum (9/20 post): That gum was printed in four color layers; Magenta, Yellow Ochre, Cyan, Magenta. Exactly what was in my thinking at the time, why I didn't run a black layer, or why two Magenta layers, is but speculation at this time, even for me. What generally drives my thinking at the time of printing is how the print image is moving along at that given layer and what the next color will do to that image, where I want to keep the pigment away from to retain whites, and other considerations. I say it often, gum printing is technically a photographic watercolor. It's a photographic process by virtue of using a negative to arrive at the printed image. The gum process, however, works the same as watercolor rules, utilizing subtractive color theory, and retention of paper base white in areas for later coverage, or through the entire process to represent pure white.
Process Notes;
Paper; equivalent of Arches 140lb hot press watercolor paper.
Sizing; (2) sizing coats of 5% Knox Gelatin solution @ 120 deg; 30 secs to 1 min
Gum Solution; approximately 30% mixture {30g gum to 100ml distilled water)
*Premixed gum Arabic is usually measured in Baum. I do not know anything about Baum beyond it being a measure of viscosity. The premixed gum I've seen online is listed as 14 Baum, and if I had to make a guess as to it's % measurement, it would be that 14 Baum roughly equals 30% by weight.
That part is important, being the gum mixture, with pigment mixed in, is mixed 50-50 with the sensitizing solution, which is potassium dichromate (13%) in water, and mixing water with gum effectively cuts the viscosity in half. Half of 14 Baum is thin to my method of printing. This print was a bit further along than the first few I made, yet still fairly crude to later prints. I was still learning about the balance between sizing and binder thickness. One of the better habits I began early on, was marking the printing layers, a 1" strip of the finished gum mixture painted along the edge of the paper before each printing, leaving a permanent color strip after printing, showing the exact color, and in which order of printed layers.
Because of the thinner gum mixture carrying the pigment, the pigment wasn't fully suspended or contained within the gum mixture, thereby losing some of the transparency otherwise seen. That pigment was unable to penetrate and stain the paper due to the heavy sizing. *Heavy to my methodology. I use half that now. If the paper had been sized at 2 1/2% solution, along with the thinner gum mixture carrying a perky amount of pigment, the outcome would likely have seen some real paper staining. At exactly what point that would happen isn't clear, until it is done, for visual inspection.
It could be that printers prefer this look in a print, and can replicate it by following the process notes above. I found it interesting but not where I wanted to go. Using a paper negative obviously works, and I would say rather well actually. However, compared to a digital negative, there is no comparison between the two for added density control and acutance, offering up superior texture and detail with the latter. The print in this discussion is below to see what the information above represents.
Gum Dichromate Print ~ "Sunset Fern Ridge"
5% Sizing; (2 coats) ~
30% Gum Mixture ~
4 Color Run; magenta, yellow, cyan, magenta (for sky)
Color strips along the bottom of the print showing print run color/order;
Next post will be with an example of how I do it today.
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