The chapter called “Casein printing” of Sarah Van Keuren’s book “A Non-Silver Manual: Cyanotype, Vandyke Brown, Palladium & Gum Bichromate with instructions for making light-resists including pinhole photography”, written by Rosae M. Reeder.
Casein printing is a non-silver photographic process that works well with dry pigment. Casein is made by breaking down the protein in milk with ammonia to create a glue-like substance. Pigment is added for color and ammonium dichromate is added to make a surface photo-sensitive.
Types of Negatives
Because ammonium dichromate is the sensitizer, a negative must be used for exposure. A negative can be produced in any number of ways. Some examples are:
- Traditional photo negative — photographs taken, then developed. Make a contact print or expose images to larger negative film (lith film, x-ray film, etc.).
- Inkjet negative — image must be scanned into the computer and output as a negative in grayscale onto inkjet transparency film.
- Hand-drawn negative — using a sheet of acetate or frosted mylar, make a drawing with black medium such as acrylic or ink. (If you are using acetate with liquid medium such as ink, you may need to add a very small amount of Photo-Flo or liquid detergent to break the surface tension and allow the medium to adhere to the acetate.)
Types of Pigment
Any pigment that can be incorporated into this mixture can be used. It is recommended that only water-soluble pigments are used — or dry pigment.
- Watercolor—use less than you might expect to use. If you do not size the paper for these prints, some staining could occur.
- Gouache — can be used instead of watercolor. It is more opaque and also has the possibility of staining.
- Dry pigment — any dry pigment can be used. Store-bought pigments for making oil paints are suitable; common dirt and soil work very well. Xerox toner is quite suitable for making a pleasing gray-to-black. When using the dry pigment, add a little Photo-Flo so that the surface tension of the water is broken. This will allow for better incorporation of the dry pigment.
Materials needed to make the casein are as follows:
- glass jar with lid (mayo or peanut butter jars are good sizes)
- powdered milk or plain large-curd cottage cheese (whole milk or low-fat work)
IF YOU ARE USING COTTAGE CHEESE, SIMPLY FOLLOW STEPS 3 THRU 6 BELOW.
- plastic spoon or stick
- glacial acetic acid (stop bath without the indicator) for use with powdered milk only. (White vinegar can be used in place of the glacial acetic acid but the curdling time can be much slower.)
- old nylon stocking for powdered milk or sieve for cottage cheese
- ammonia, plain
- 2 medium-sized bowls for mixing and straining with powdered milk
- rubber or plastic gloves
Mixing (Gloves should be worn for this procedure.)
- Mix powdered milk according to the instructions on the box with tepid water. Be sure to mix thoroughly so that all powder has dissolved.
- Add glacial acetic acid to the mixture until it begins to curdle. Try to obtain large curds if possible by pouring a little of the acetic acid in at a time.
- When the mixture curdles enough, place the curds in the old nylon stocking (or a sieve for cottage cheese) and squeeze out as much liquid as possible. The squeezing should be done while rinsing under cold water. Continue to rinse until the water runs clear through the stocking (or sieve) and curds.
- Open the stocking and place the curds in a jar. Make sure you have squeezed out as much water as possible.
- Cover the curds with ammonia. Be sure to push the curds down into the jar so that
they are totally covered with ammonia. (The thickness of this liquid will depend upon how much ammonia you add to the curds. If you are using dry pigment, I recommend a thicker mixture because this will allow you to create heavier textures and it will allow those heavier areas of pigment to adhere to the paper better. The thinner mixture with dry pigment added, will give you some reticulated marks where the pigment has rested.
- Let the ammonia and curds mixture sit for at least 24 hours uncovered in a cool dry place. In front of an open window with minimal light coming in or high on a shelf are good places.The result will be a gluey yellowy-colored liquid. Label and refrigerate but bring to room temperature before using.
This mixture is now suitable for incorporating the ammonium dichromate and pigment.
Coating the Paper
Many different types of paper can be used for this process as long as the paper can be immersed in water and soaked for a period of time without disintegration. Printmaking papers are highly recommended.
Use a small dish for mixing the casein, pigment and dichromate for coating paper.
- Add some of the casein mixture to the dish.
- Add your choice of pigment. If you are using the dry pigment remember to add a little Photo-Flo as well (just a couple of drops). REMEMBER, the intensity of the color is determined by the amount of pigment used. Also, try not to go too heavy on the first layer. Exposure times might need to be lengthened if your coating is too dark. AND if you go too dark on the first layer, difficulty in achieving multiple layers of exposure may arise.
- Add the dichromate mixture (see “Gum Bichromate” chapter under ‘Safety and Mixing Dichromate Sensitizer’). You could measure one to one, dichromate to casein.
- Mix well and coat paper with a soft wide bristle brush. Haké brushes work well for this. The casein can be a bit thick and you want to use a brush that can grab the mixture and coat evenly without too many passes.
- Let the coated paper dry thoroughly in a dark area before exposure.
Exposure time will vary depending on your medium of exposure, coating of the paper, and pigment used. A test is required to get the best result per negative. These prints can be exposed anywhere from 10 seconds to 1 hour. The exposure time for casein can be much faster than gum or other non-silver processes. Be sure to take this into consideration while testing for exposure times.
Developing the Prints
Casein prints should be developed in water.
- Fill a tray large enough to accommodate the print in with water.
- Immerse the print under the water image side down. This is done so that the pigment and the casein will fall off of the paper as the casein is permeated by the water.
- Developing can be pushed by removing the paper from the water and going over the image area with a stream of water. If that doesn’t clear the image, let it sit wet on a horizontal surface for a couple of minutes, and then stroke the image lightly with a soft wet brush, then a hard bristle brush or fingers (with gloves). Be careful with scrubbing the surface of the print so as not to remove important parts of the image or paper fibers.
- Once the print has been developed, hang to dry.
Layering effects seem to achieve the best results with this process. Experimentation and exploration of assorted pigments, thickness of the casein mixture, different types of casein (cottage cheese, powdered milk), assorted papers and exposure time will all lend to the many different effects that can be achieved.