The 19th century gum bichromate process in 21st century concept and techniques

Christina Z. Anderson gives us the "why and how" of the gum process, including making negatives.

It is surprising how few people know what a gum print is. Many photographers are not even familiar with the process!

This is probably not as true of those frequenting AlternativePhotography.com. because there are already some excellent articles on gum on this website. This article will hopefully be a compliment to those –
sharing the way I practice gum but also addressing such things as why I gum print and what images might look best in gum.

For those who are reading a gum article for a first time, and have no idea what gum is all about, a brief description is in order. Gum prints could be called " photographically controlled watercolors"
. Even though the image may resemble a color photograph, it is only a fabrication of layers of pigment and hardened gum Arabic. It is in some ways closer to painting than photography. 

Gum Arabic is mixed with watercolor pigment and a photosensitive substance called ammonium dichromate, and brushed onto watercolor paper. When exposed to light in contact with an enlarged negative, where the light hits the most, the gum hardens the most and creates the shadow areas of the image. Where the light hits the least, the gum and pigment wash away proportionately, leaving the highlights of the image.  The " development" of the print isn’
t carried out in darkroom chemistry, but merely plain water. In the water bath, the image reveals itself over a period of an hour or so development, little by little, as the unexposed highlights first wash away and then the softer midtones also dissolve off in various depths. What results is an image that looks surprisingly continuous tone.

This exposing and development process could be done once for a monochrome image, but more often it is carried out two or more times, layer upon layer, with development and drying steps after each exposure. This produces a much richer print. For a tricolor print there must be three layers – blue, yellow, and magenta. Often a fourth layer of either blue or black will be added to give a print extra punch, or perhaps another color to correct the color balance slightly. Even as many as 30 layers can be used, although this is generally overkill. But it is easy to realize that a gum print is time-intensive, and much different than a traditional color photograph.

When a gum print is finished and dried, it is the most stable and archival photographic process there is, alongside carbon and platinum. It is, therefore, a good photographic investment, with none of the worries that accompany a traditional black and white or color print, which are subject to silvering out, brown spots, severe fading, and other such conservation nightmares. As long as lightfast pigments are used, the gum print will last as long as the paper it is on.

Why Gum?

I can only speak for myself to answer this question, because there are so many reasons why gum bichromate is such an intriguing process.

Challenge: gum printing is variable enough to keep the process always interesting. It is not a one-shot process where if it isn’t right, the print gets thrown away. There is always room for more experimentation, and many chances to get something you did not expect in the first place.

Color: Gum can be so color-accurate that it resembles a traditional color print, but it also can have the tendency to a sometimes odd, offbeat or nostalgic color palette. You can capitalize upon this by using yellowed, faded tones to express nostalgia, but you can also use pale, ethereal tones to express spiritual ideas, or bold, acid colors to lean towards Pop Art. In fact, with gum printing, color choice is akin to oil or watercolor painting- essentially unlimited. As you can see from the images accompanying this article, I have been very influenced by Pop Art’s bold colors and use that palette in a lot of my work.

I believe that the locus of emotion lies in color. We as humans are very subconsciously responsive to color to " read" an image’
s meaning. With gum printing it is so easy to change the emotion of a piece just by pigment choice. I like that kind of control. Color and mood are under my control instead of the camera.

Texture: Gum can be made perfectly smooth, but that would be missing the boat. It has a textural quality that can be capitalized upon, an inherent juicy, glossy, and sometimes spotty, streaky, grainy nature that makes it very painterly. In fact, its textural quality provides the ambiguity- is it a painting or a photograph? At my first show viewers would talk to me about " my paintings". This quality can be enhanced even further by brushing the developing print while in a tender state, or leaving the brush marked borders visible in the finished, matted work.

Transformation: An ordinary image becomes something unique through the gum translation of texture and color. This happens with each and every print. Gum is a one of a kind process. Copies can be made but no two are really exact. The transformation is individual and sometimes unpredictable. I like this uniqueness and this sense of surprise.

Changeability: At any time I can go back to a print and change existing information by scratching out a layer here, adding another layer there. Much like a painting, a gum print can be a work progress until it is hanging on a gallery wall. In fact, when I get a print that I like, I make sure to mat it so that I resist the urge to revisit it at a later date!

Meditation: Gum printing is a very meditative, hands-on process for those who derive pleasure in process, in remaining aware and in the moment while expressions of beauty occur. While working laboriously on a print, layer by layer, day by day, I become intimate with the image as it ingrains upon my mind, eyes, and hands. I lose sense of time and have that "flow" experience.

This is important today where disconnection or mediation seems to be the going way of life. Text messaging and email are rapidly replacing the phone call and the handwritten letter. It may seem we are able to connect at a greater as well as instant level, but in a way we are connecting with this go-between or mediated environment.

Anachronism: There is something deliciously anachronistic about using a 19th century process in the 21st century, about spending days making one print at a time in history when we don‘t have to do so. It is akin to the Buckskinners who travel to " conventions" where they live in teepees, using all of the accoutrements of centuries ago. I feel very connected to the beginning of photography in the 1800′
s and all of those gummists who went before me.

What Images?

The simplest answer to this question is: any! The more complex question to ask is this: is the image you are about to work on worth the effort? This may seem simplistic but most viewers are visually savvy enough to know what I mean.

But then again, I have spent the last year photographing trash in parking lots for my Parking Lot project, some of which you see in this article, and I guarantee there are some readers who wouldn’ t have a clue why I would photograph and make gum prints out of these! See my website christinaZanderson.com for the complete project as well as artist statement.

When I am out photographing, I instantly know which images will benefit by gum, so there has to be something that I can qualify about the right image for gum. These qualities come to mind: an image that does not rely on itsy bitsy detail, one that has a good focal point, larger objects, and where color, texture, form, and emotion are important conceptual elements. A rule of thumb might even be this: an image that would make a good painting would make a good gum print.

Steps to Make a Gum Print

The reader will find that in the field of gum printing, there are as many different opinions as there are practitioners! Of all the processes, it is probably safe to say that gum printers are the most passionate and, shall I say, obstinate, of the lot. This is probably because there are so many variables in the making of a gum print and also so many errors that can occur that once a gum printer finds his or her way to make a successful print, it is easy to think it is the only way. If you are a perfectionist, expect frustration along the way. The gum process can be done so perfectly smooth that it looks like a color photograph, but if this is your only goal, you will bypass the rich rewards of the chance imperfections that gum provides.

To make my gum prints I generally use Fabriano Artistico Extra White Hot Press 140 lb. paper because it is heavy duty, well sized, stable in dimension through repeated water baths, and provides me with everything I need in a gum paper without being too costly. I use a 15% ammonium dichromate mix, and a 14 Baume gum.

All watercolor pigments work fine, but I generally settle on a red, blue, yellow, brown, and black in 15ml tubes from M. Graham, Daniel Smith, Maimeri, Winsor Newton, Schmincke, and others. High quality, lightfast pigments are a must. I keep an arsenal of around 30 or so pigments that I use-warm and cool forms of all colors-but for a beginning gum printer only 5 are really needed.

I always shrink and size my paper with a 3% gelatin, hardened with 6-24ml of 2.5% glutaraldehyde per liter of gelatin. Glutaraldehyde is obtainable from Photographer’s Formulary (photoformulary.com), in a 25% solution.
Add 1 part of this to 9 parts of water immediately, and outside, to make the 2.5%. I brush size my larger sheets of paper with this hardened gelatin. The hot, hardened gelatin remains in a dedicated thermos and bit by bit is poured out at time of use. That way the fumes are minimized. This MUST be done with excellent ventilation. If my pieces of paper are 11×14 I tray size with unhardened gelatin, and then the following day soak these sized pieces outside in a tray filled with a gallon of water and 100ml of the 2.5% glut. Pieces soak for 5 minutes and then are hung to drip dry outside to again minimize any fumes. This works fine even in a Montana winter.

Sizing takes time, but it assures me that my gum prints will not develop stained highlights with repeated layers. There is nothing more frustrating than not sizing and finding that the 4th layer of the print leaves the highlights dulled with color after all that time. Better to spend the time at the offset by sizing.

I make my negatives on Pictorico OHP transparency, and apply a custom calibrated curve to them that I have derived from my work with the Precision Digital Negative system (PrecisionDigitalNegatives.com). A curve is necessary because gum bichromate has really only a 4-6 stop range, so the negative information needs to be compressed into 4-6 stops, to be expressed fully. If you make gum printing your process of choice, I strongly suggest you invest in the PDN system or in Dan Burkholder’s books (DanBurkholder.com).

There is a low-tech way with Photoshop for beginning gummists to get an acceptable negative. It is a "lossy" way of creating digital negatives—some tones are lost in the making of the negative—and therefore is not the best method for making negatives, but it will do for a first foray into gum printing and even beyond. (Those who do not have Photoshop can perhaps just play with Brightness/Contrast tool in their program of choice and reduce contrast visually until the negative looks very dull and flat.)

If you are printing a monochrome, one negative gum print, get the image ready in Photoshop. Desaturate the image (Image>Adjustments>Desaturate). Then invert to a negative. Go to Layer>New Adjustment Layer>Curves and make the bottom left point " Input 0 Output 25" and the top right point "Input 255 Output 200" . The bottom left point of the curve when raised to 25 makes the blacks of the negative (highlights in the print) less dense and the top right point of the curve makes the clears of the negative (blacks in the print) more dense. The contrast of the whole print is lowered as well. Thus the highlights are able to print with detail before the shadows block up.

If you are printing a tricolor gum print, first invert the positive, and then go to the Layers palette, choose the Channels tab, and go to Channels>Split Channels. This will result in 3 grayscale negatives. Convert each grayscale negative to RGB (Image>Mode>RGB), and then apply the curve adjustment layer as per above. The "R" negative prints the blue layer, the "B" negative prints the yellow, and the "G" negative prints the magenta layer.

I developed this method of making simpler negatives for short workshops wherein I cannot teach the PDN system at length.
I do teach only PDN at my university because I have the whole semester, but in a weekend workshop I needed a way to produce an adequate gum negative.
I tested this well—my entire Parking Lot series on my website is printed using this method. It works adequately for a low-tech, lossy method, and gum is the most forgiving of all processes.

I mix my gum/pigment mix with the dichromate 1:1. How much pigment is used in the gum/pigment mix is a matter of choice and whether the layer is to be pale or punchy. I use about 1/2 teaspoon of combined mix for an 8×10, and brush it on with a 2"
stitched Connoisseur 150 series hake brush. Personally, I feel a lot of gum problems come from too thick of a layer. I immediately put my brush in water and my gum brushes have lasted for years.

The layer dries for anywhere from seconds with a cool hair dryer to 15-30 minutes by air, depending on the relative humidity of the room. As soon as it is dry, I expose it. Each layer’s exposure is usually about 5 or 6 minutes in a UVBL exposure unit.

I develop immediately, first with the print face up in the water for 1 minute while the dichromate immediately leaches out, and then face down the rest of the time. I use the same tray to leach out the ammonium dichromate for all my prints. The water gets very yellow and grungy but does nothing to the print. When the majority of the dichromate is out of the print in that first minute, I do the rest of the development in my bathtub. The nice thing about this method is that there is less of a disposal issue—the tray of dichromate water can be evaporated to very little liquid and stored in a labeled container until full and ready for disposal. Check your state’s disposal regulations.

My usual development time is 1/2-1 hour or more. Often I use a spray bottle to hurry along the development, but this is done right away, after the print has soaked maybe 5 minutes and the layer is still quite stable. I check the print every 10 or 15 minutes, lifting it completely out of the water. I usually finish the print with small detail brushes to clear the highlights. I have found Royal Langnickel SnoWhite 4510 brights to be incredible for this-soft yet firm.

I mostly print three layers: blue first, yellow next, then magenta last. Lately I have been printing a pale cyanotype base layer which provides nice detail and sharpness as well as ease in registering my subsequent coats by eye over a light table. But I still print my three layers of tricolor gum on top of this. I use Scotch removable tape to secure the negative to the paper in registration.

When development is done, I hang the print on hangers to dry. A print dries darker and duller than it looks in the water. I trim the paper evenly around the gum print, sign the bottom with my name and title of the piece, bag it in an archival plastic sleeve from Light Impressions, and the gum print is done.

This is a very brief summary of making a gum print, and perhaps serves the purpose only to whet the appetite, as each paragraph herein could be an entire chapter. My hope is that the description and the images will do justice to the intriguing capabilities of the process and encourage the reader to do further research and experimentation.

A more comprehensive description of the process can be found in my book Alternative Processes, Condensed. In the works is a book devoted solely to gum printing as well. For information about books as well as my personal work, please refer to: christinaZanderson.com.


Experimental Photography Workbook

by Christina Z. Anderson

A technical book recommended both for beginners and pros


Alternative Processes Condensed
A Manual of Gum Dichromate and Other Contact Printing Processes

by Christina Z. Anderson

Packed full of information



One Comment

  1. Dean Drumheller
    Posted May 30, 2011 at 4:34 am | Permalink

    Thanks for the great information. I’m new to gum printing and plan to make 4 negatives through a 4×5 view camera for my first gum printing. These will create: black, red, green, and blue layers.

    To filter the RGB negatives during the exposure, do I use filters the same color as my pigment: red, green, blue?

    Or do I use opposite filters when imaging: cyan, magenta, yellow for printing RGB pigments?

    Thanks, Dean

One Trackback

  1. By A Simplified Three Color Gum Curve — f295.org on December 12, 2011 at 5:12 pm

    [...] color gum printing. It’s derived from Christina Z. Anderson’s method (as outlined in this article) and will make the negatives more suitable (flatter) for the gum process. There are other more [...]

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