Silvergum Printing

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"Gum Bichromate Process ...The method may be summarised as follows: — Ground pigments are mixed with a thin mucilage of gum-arabic, and a little soluble bichromate, this mixture being applied to the paper as a thin wash.  When dry, the paper is exposed under a negative, and the picture is developed by soaking in water (cold, warm, or hot) until the unexposed portions of the pigmented gum are sufficiently washed away."

The Dictionary of Photography and Reference Book for Amateur and Professional Photographers, 9th Edition. E.J. Wall, 1912.

It seems only natural to return to the beginnings of emulsion history and combine that with an art form that is essentially unchanged from its own beginnings, and then add digital color separations to create something brand new.  I'm calling it Silvergum; three-color gum over silver gelatin emulsion.

Until now, gum has not gone well with silver gelatin (at least so far has I've been able to discover).  Commercial papers based on baryta stock are too slick for the gum to adhere.  Gum with platinum or cyanotype have been the main expressions of the gum-over idea.  But, handmade emulsion on Fabriano Artistico HP watercolor paper (and I'm sure there are other great papers) is a perfect substrate for gum.  The emulsion is as hard as nails so there is little risk of staining and the original print acts as a registration base and as a 'K' layer that gives the final print a beautiful depth.

Gum printing fits with my idea of a perfect craft.  It is possible to get started and continue forever with the most basic of tools and space.  I did all my first explorations with one good brush and a photoflood bulb.  I've moved on to three brushes! and a UV printer from  (Jon) Edwards Engineered Products.

There are so many excellent sources of information on the basics and beyond of gum printing, there's no need to go into most of that here.  One point that may be different from other gum printing is the ease of negative registration.  After each step, dry and flatten the print in a dry mount press. (A clothes iron over the print inside a couple of sheets of 2-ply mat board or similar, followed by flattening under a weight works just as well). On a light table, register the appropriate negative (blue, red, or yellow) with the image and tape it at the top with film tape.  For coating, swing the negative up and out of the way while you brush on the pigment and then dry it.  (I use a hairdryer on low.  I live in a very humid climate and the darn things would never dry without some help.) When the layer is dry,  swing the negative back down - it will still be in perfect registration - and place the negative/paper sandwich in a contact printing frame and expose to your light source.

Negative registration is greatly improved by the addition of digital negatives to the process.  With each step, the paper shrinks just a bit.  I've calibrated that shrinkage (and it's very consistent) for Fabriano paper and my work flow.  Starting with a 3.5 inch high print in mind, I make the original b&w negative 0.5 mm longer and 0.3 mm wider.  There is considerable shrinkage during the first step.  With each color layer there is just a bit more shrinkage, getting less with each pass.  You would think it wouldn't be enough to matter, but perfect registration makes an enormous difference in the finished print, and since with digital negatives custom sizing is one-step easy, why not?  A little trial and error and good notes will quickly establish the calibration that works best with a particular set of materials and workflow.

The following three pages cover the techniques of silvergum printing in increasing detail, from basic 3-color and basic 5-color, to an expanded 'Silvergum Tutorial' on page 4.

April 4, 2010. Material Info Update - Fabriano Artistico papers:  After a number of months of testing, I am convinced that Fab Art paper has been changed.  I started out with Fab Art X-white HP paper four years ago and have coated just about every variety of emulsion imaginable on it.  As ugly as some emulsions have been, one thing I felt confident in saying was that they were bullet-proof no bubbling, frilling or lifting.  That changed about four months ago.  I started getting tiny bubbles of lifting emulsion during washing.  I originally thought that one of my ingredients had gone old, but after replacing all of them, one by one, I did a whole range of paper samples again.  With any given run of emulsion, only the Fabriano Artistico papers develop bubbles.  I love Fab Art paper, so I pushed through for a work-around solution.  Bubbles are eliminated, or at the least greatly reduced if I use hardening fixer and follow with a 'speed wash' protocol (short pre-wash, archival washing aid, shortened final wash, squeegee, dry). dwr

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