Gum Bichromate

Archived Posts from this Category

Busy With Teaching

Posted by on 29 Mar 2009 | Tagged as: Gum Bichromate

I’ll be teaching full-time for a few weeks now, and don’t have much time for alt-photo work of my own. However, I’ve been thinking of gum printing too, and here are a couple of things that I must consider to get students involved more easily:

Paper: Got to find good, dimensionally stable paper with good wet strength.
Sizing: Thought I could manage without extra sizing, but it looks like it’s just necessary to size certain papers. Also, I need to determine which sizing method to use.
Pigments: Finding an assortment of good quality non-staining pigments.
Negatives: Proper correction curves; it may be necessary to generate separate curves for each color (in 3 and 4-color work) instead of single generic curve common to all colors.

By the way – good news about Varn gum! We can get it again – our supplier was able to make a special order from Germany. It will make our life a little bit easier, with no need to mix the gum from powder or lumps…

Gum Inconvenience

Posted by on 18 Mar 2009 | Tagged as: Gum Bichromate

In gum bichromate printing we have been using Varn 14 Be lithographers gum solution, bought in 10 liter containers. From our supplier we heard that it is not available any more, and they sent what is supposed to be a substitutive product, “Agum O” solution by Hanns Eggen GmbH, Germany. The supplier assured us that it would be the same stuff, with same properties as Varn had.

But it isn’t! I made some tests with my standard pigment/gum/dichromate mix that I had used with Varn gum.

020209_testi-1.jpglinel-test2-030209.jpg
Some step table tests with “Agum O” gum and Schmincke and Linel pigments.

In my quick tests with step wedges I got very stained results. No matter how I mixed the sensitizer my pigments always stained the paper base heavily.

I tried to google for some information on “Agum O” but couldn’t find much. This gum feels a bit watery compared to Varn. Some sources refer to it as synthetic gum, and on this Finnish web page it is said to contain also dextrine in addition to gum arabic.

I couldn’t use this gum! So I decided to mix my own. I bought gum arabic as fine powder and mixed it with water at 1 + 2 (100g gum + 200ml water). The solution became somewhat thicker than the standard 14 Be gum, but some gum printers prefer it at this strenth.

I will need to recalibrate my gum printing workflow, so I guess it’ll take a while until I get some results posted here…

Down to Gum Business Again

Posted by on 06 Mar 2009 | Tagged as: Gum Bichromate

After a few weeks winter break it’s time to get back to gum printing!

samos_wall-2.jpg

This picture was one of my test images when trying the curves introduced in the previous gum printing post. The picture was taken with a Nikon D70, it is a RAW file, and has been slightly processed by increasing color saturation and vignetting the corners a bit. Cyanotype was used as the cyan layer.

Color separation was made by splitting RGB channels into three separate grayscale images. A correction curve created by ChartThrob was applied to each image. The images were then inverted to negatives and printed on CopyJet transparency. The negative from R channel was printed in cyanotype, B in gum bichromate with yellow pigment, and G with magenta pigment, in this order.

samos_wall-seps.jpg
The three separation negatives.

samos_wall-c.jpgsamos_wall-cy.jpg
The first two print layers: Cyanotype and Cadmium Yellow.

samos_wall-sml.jpg
Jalo Porkkala: Samos Wall, tri-color gum / cyanotype.

Magenta as the topmost layer.

The outcome is a bit powerless and muddy – color balance and saturation are not quite there yet – the Maimeri pigments chosen may not be the most adequate ones for the job. Also printing each color layer twice could yield better color depth.

Tri-Color Gum Preparation

Posted by on 02 Feb 2009 | Tagged as: Gum Bichromate

Some testing with pigment saturation and tone range for tri-color gum printing. The aim is to print in “full color”* with only three separation negatives, using CMY (cyan-magenta-yellow) pigments, without the K (black) component normally used in commercial color separations. I am trying to create black by mixing from the three color layers. I will use cyanotype as the bottom layer, diluted with water to balance it better with the other colors.

3-color-gumtest.jpg
Exposure tests on Cyan (traditional cyanotype diluted with 4 parts of water), Magenta (Maimeri Magenta), and Yellow (Maimeri Cadmium Yellow).

Once the pigments and their strength are chosen, and a working correction curve created for each separated negative (e.g. by ChartThrob script), they can be tested by printing all CMY colors on top of each other. If the pigments were chosen succesfully and the negatives curved properly, the result should be, more or less, a gray balanced image.

3c-gum-c.jpg3c-gum-cy.jpg

3c-gum-cym.jpg

Cyan (cyanotype, top left), Cyan+Yellow (top right), and Cyan+Yellow+Magenta (left), each layer with its correction curve, respectively.

*A gum printer’s “full color” doesn’t necessarily look like properly balanced color photograph (if it did, why bother gum printing at all), rather it is his/her interpretation of subject colors, and can vary quite a lot, depending on pigments chosen. That said, also naturally balanced, very realistic “photographic” colors are possible to achieve.

After a Hotter Look

Posted by on 06 Jan 2009 | Tagged as: Gum Bichromate

The next logical step would probably be so-called full color gum printing – making three or four color separation negative set and printing with pigments resembling (more or less) the “real” CMY(K) process colors. We’ll definitely try that too, but meanwhile, I’d like to quickly introduce another slightly different way of building up the desired tone range with the single negative technique – starting with the lightest pigments and proceeding towards the darker ones.

cupidos-1.jpgcupidos-2.jpgcupidos-3.jpg
Printed with Maimeri powdered pigments. The first layer is Cadmium Yellow, the second one Alizarin Carmine, and the third one Prussian Blue.

cupidos-4-sml.jpg
Jalo Porkkala: Cupidos, gum bichromate print.

The fourth layer is another lay-down of Prussian Blue, meant to increase contrast a bit, and cool down the shadow tones.

I kinda like the tonality, although it is not quite what I had in mind; I wanted more red, somewhat hotter look – these guys obviously are a pair of nasty cupids from hell after all. Maybe I´ll add a layer of fiery red one day…

« Previous PageNext Page »