What’s new Gum bichromates Breast milk and the casein print

Breast milk and the casein print

Writer and photography / Christina Z. Anderson

Christina Z. Anderson – author of Gum printing and other amazing contact printing processes, amongst other books – experiments yet again and this time uses breast milk to make casein prints or cottage cheese.

Over the last two decades I have concentrated my photographic practice and research in the area of 19th century photographic processes, most often gum and casein dichromate printing. Casein and gum Arabic are colloids that if mixed with ammonium, potassium, or sodium dichromate will become photosensitive and harden in the presence of light. This hardening quality can be used to print a photographic image. The colloid and dichromate are mixed with a watercolor pigment, brushed onto watercolor paper, and exposed to light under a negative. Where the light hits the most, more hardening occurs. Where the light hits the least, less hardening occurs. This proportional hardening results in a positive image of the negative.

Casein print using cottage cheese
Lil’ Pumper, tricolor casein print © Christina Z. Anderson 2013. Casein used in this print was precipitated from cottage cheese.

Today there is a renaissance of these forms of hand-coated, light-sensitive processes because of the ease of digital negatives and handy exposure units that use fluorescent UVBL tubes. The processes can now be done without bulky cameras and film, extended darkroom hours, and fickle sunlight.

For those well-versed in gum printing, although casein and gum are both colloids with this hardening capability, casein is quite different in practice. Casein is ultra-fast in exposure and development. A one minute exposure and a fifteen minute development is normal. Casein is slightly opaque and brighter in the final result (think milky-white). Casein is dead-matte if powdered pigments are used (watercolor pigment contains some gum Arabic which lends a bit of gloss to the print). Casein is very fine-grained. And casein is tenacious as hell, clinging to plastic and paper with all its might, even when subject to brushing and scrubbing.

Casein curdling using vinegar
Left: vinegar added to breast milk, note little curd coagulation. Right: vinegar added to cow’s milk, note instant curd coagulation or “curdling” as it is called.

I wrote about the process at length in my 2013 Gum Printing and Other Amazing Contact Printing Processes, the first full-length treatise on casein in the literature to my knowledge. Previously gum printing was my process of choice and although it still is, I was happy to find a different colloid to use that was so inexpensive and readily available. Trade embargoes or wars might some day make gum Arabic scarce, expensive, or­ – perish the thought – unavailable. Cows probably won’t disappear from the American landscape.

One day I received an email from a woman asking if breast milk would work in a casein print. Not being one to say “no” if I had not tried it myself, I surmised it should work. Milk was milk, wasn’t it?

And furthermore, using breast milk in a photographic process seemed a rich feminist concept. It even had commercial implications—think of baby portraits out of mother’s own milk! In my child-rearing days I nursed all my babies and was a La Leche League leader for 12 years, counseling mothers about the benefits of breast over bottle. “Breast is best!” was our mantra, and it took decades for the rest of the world to agree. Unfortunately my nursing days were long gone and advertising for a ready supply of breast milk seemed a little… weird, not to mention potentially expensive.

Montana State University where I am an associate professor is a research university, meaning high value is placed on research and all faculty are expected to do their share. This qualified as research, didn’t it? I contacted the former chairwoman of the Women’s Faculty Caucus, and Political Science professor Sara Rushing, who was gracious – and smart – to take the time to post a notice of my odd request in the MSU Family Care Room, a place where nursing mothers can relax and nurse their babies out of the workplace. Within several weeks I got a response from Research Engineer Michelle Akin who was currently lactating and willing to donate. In return I would print for her a tricolor casein print of her nursing baby. I also received milk from Abby Lee who gave birth to a darling daughter during my experiments. This way I could make sure my results were corroborated with another human source.

Straining casein for photography
When cow’s milk is poured into a knee-hi nylon stocking the whey instantly drains off, leaving the curd behind which is about the volume of a plum per cup of milk. Top left shows the curd left from cow’s milk curdling. Top right shows the  curd left from breast milk curdling—essentially none. Bottom left, the remaining white curd from a cup of cow’s milk, and bottom right, the remaining liquid whey.

I received the breast milk and followed my normal casein printing steps. First the casein is precipitated out of the milk by the addition of an acid. Just a mere tablespoon or two of household vinegar will curdle milk immediately. The curds and the whey separate. The whey is drained off and thrown away, and the curds which remain—the casein part—are then mixed with a small amount of household ammonia and water to liquify the curds into a solution about the consistency of half and half. This casein solution is mixed with potassium dichromate and watercolor pigment, brushed onto watercolor paper, exposed to UV light under an enlarged negative, developed in plain water with a bit of scrubbing and brushwork, and voilà, an image results because of the ability of dichromate in the presence of an organic to harden the organic when exposed to light. The voilà part is an exaggeration because there are actually three separation negatives used to print at least one red, yellow, and blue layer over a period of a day or two or three.
 What I discovered was that my untested hypothesis that breast would be a suitable casein source for casein printing wasn’t quite accurate. First, when vinegar is added to cow’s milk, the casein curds precipitate out of the whey immediately, or at least within an hour. The volume of the precipitated curds equals about the volume of a small plum per cup of milk.[1] I couldn’t get the breast milk to precipitate any curd to speak of.

Nevertheless I forged ahead, mixed it with powdered pigment, and got a very weakly colored print, hardly suitable. The surface of the print was somewhat oily as well.

Practice before research? Not a good thing. I found through subsequent research that human milk is much lower in casein than cow’s milk. For starters, ounce for ounce, human milk contains less than 1/3 the protein of cow’s milk. This makes sense, since babies take years to grow big and cows take months. This isn’t all. Human milk is 28% casein/72% whey; cow’s milk is 82% casein/18% whey. In other words, the whey to casein proportion in human milk versus cow’s milk is flipped. Not only is there much less protein to be had in breast milk, there is much less casein to be had in the protein. The casein content amounts to about 0.4%[2], almost not worth the vinegar used to precipitate it.

The other issue that increases breast milk’s unsuitability for casein printing is that it isn’t skim milk. Fat in milk is not a good thing for casein printing. During precipitation of the curd, the fat binds with the curd.[3]  In fact, casein printing works best with skim milk or fat free cottage cheese, with whole milk a less suitable choice even if it still works. Breast milk is nice and fatty, 3-5%. This fat was the source of the surface oiliness I observed.

Stouffer step wedge for casein photographic print
A Stouffer’s step wedge is a film negative used to calibrate exposure time in contact printing processes. It is accurately calibrated in 1/3-stop increments; 3 “steps” equal a halving or doubling of exposure time. Here are four printed step wedges, two in ultramarine blue and two in red iron oxide pigment. The left side of the Stouffer’s steps 1-16 is done with cow’s milk and the right side is done with breast milk. All step wedges were scrubbed harshly during water development to test the sturdiness of the layer. Where cow’s milk prints bright, definitive steps, breast milk has nothing much to harden with exposure and the pigment merely sinks into the paper fibers and stains. There is a modicum of image produced so breast milk can be used albeit unsuitable.

My conclusion is that the breast milk print will probably not go down in history as the new printing process of the 21st century with my name attached to it. There will be no fame or even infamy. It probably won’t increase the research rating of Montana State University and win me multi-million dollar grants. The old adage that breast milk is for babies and cow’s milk is for cows still remains true. There is no better food for humans. For casein printing, however, cow’s milk is (I can’t resist a pun) the udder best. This is not to say that some form of conceptual photographic practice with breast milk can’t be done. Certainly a portion of breast milk could be mixed in with cow’s milk. Plus it was common practice to use milk whey not casein as a carrier for silver salts in the 1800s. This was replaced eventually with collodion, gelatin, arrowroot and other ingredients, but perhaps breast milk/silver nitrate printing holds rich promise for some aspiring conceptual artist. For me, I’ll happily frequent the dairy case at the local supermarket for my photographic colloid of choice.
 

Notes

  1. 7ml glacial acetic in 50ml water to 600ml skim milk (warm) will yield 13.8g casein.
  2.  

  3. Ch. 5 “Breast Feeding” pp. 127-210 of Mother and Child Nutrition in the Tropics and Subtropics, http://www.oxfordjournals.org/our_journals/tropej/online/mcnts_chap5.pdf
  4.  

  5. http://drinc.ucdavis.edu/dairychem2.htm

 

Below are extracts from the text “Mother and Child Nutrition in the Tropics and Subtropics – Chapter 5 Breast Feeding”

The full chapter can be read here: casein in human milk (pdf format: 2.3 mb).

Extract from book
Extract from book
Extract from book
Extract from book

Christina Z. Anderson is an Associate Professor of Photography at Montana State University, Bozeman, where she specializes in alternative and experimental process photography. Her books The Experimental Photography Workbook and Gum Printing and Other Amazing Contact Printing Processes have sold worldwide.

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