Read all chemical safety information and MSDS! Where a respirator when mixing dry chemicals and Glyoxal and use a fume hood or well-ventilated darkroom. Never use household or food containers for photography that would be reused with food again. Always wear gloves, eye protection and an apron. Keep chemicals safely stored away from heat and moisture and locked if around children. Also, label all of your containers!



You can use GIMP to produce 3 color separations [decompose] from a color image. It will produce RGB images that you invert: B = yellow pigment, G = magenta pigment, R = cyan pigment. For the black you can desaturate and then increase the brightness and contrast. You can also use all three (YMC) at the same time for black pigment as well. Dichromate process tends to be very contrasty, so adjusting the image highlights helps and flattening the curve. You can compensate by changing pigment to dichromate ratios and modifying exposer times.  


Paper and Sizing

Traditional Gelatin

30g of 250 Hardness type gelatin to 400 ml cold water (food grade unflavored gelatin will work too)

Let “bloom” for 30 minutes and add 600 ml hot water

Once the gelatin solution has cooled to 140F add the paper and let soak for 10 minutes

Squeegee of both sides and hang to let dry

Once dry harden with 30 ml of Glyoxal (40%) to 1L of cold water

Squeegee of both sides and hang to let dry


Gesso and Acrylic Polymer

Mix one part Gesso with One part Polymer and 12 parts water

Apply one coat with a stiff brush and dry and then a second and third coat allowing to dry between each coat. (brush horizontally, vertically and both diagonal directions)


Potassium Dichromate (K2CrO3)

11.7g of Potassium Dichromate to 88.3ml water

Store in brown glass bottle


Casein (Ammonium Caseinate)

130g nonfat dry powder milk

1L cool water

Slowly add the dry milk so it does not get lumpy

Heat to 165F and strain if needed to remove lumps


Add 12ml glacial acetic acid to 21ml water (never add water to acid! Always acid to water)

Add the diluted acid to the milk and water mixture while stirring until it coagulates

Drain through a double layer of cheese cloth in a stainless steel strainer and squeeze out excess water (cheese!)

Crumble the curd into a container and add 300ml of household ammonia stir frequently or constantly (electric stirrer) for an hour.

Refrigerate overnight



Windsor & Newton Watercolor or Gouache


Use 80 ml squeeze bottle with 60 ml liquid ammonium caseinate solution

Thalo Blue (Cyan - C) - 3.12g

Alizarion Crimson (Magenta - M) - 4.2g

Cadmium Yellow Medium(Yellow - Y) - 4.8g

Lamp Black (Black – K) - 3.12g


Mixed Sensitizer

Add 1 part Water : 1 Part Dichromate Solution : 1 Casein solution with pigment

5ml will cover 4 8x10 or about 6 8x8

(note you can use 1 part dichromate to 1 part casein pigment but it will be have more contrast and shorter exposure)


Printing Order

Generally, you should print from light to dark: yellow, magenta, cyan and black. However, I have had issues with some type of pigments either not sticking the previous color, or one washing off another. Most recently, the final black layer was completely removing the cyan layer and I would have to re-expose the cyan. I have since been starting with the black, and then Y, M, C.



Times vary with pigment, and ratio:
Watercolor Pigments (Daniel Smith) [would not recommend blue is not close to cyan and yellow coagulates.

Yellow – 75 sec

Red – 75 sec

Blue – 2 min

Black - 6 min

Gouache Pigments (Winsor & Newton)

Yellow – 75 sec

Red – 30 sec

Blue – 60 sec

Black – 2 - 3 min



Rinse in cold water until the orange color from the excess dichromate washes away (about a minute or two)

Float image side down for 10 to 20 minutes in 68F – 76F water and change the water every 5 minutes

Rinse in cold water for another 2 to 3 minutes (you should not see any more pigment washing off)

You can selectively develop areas with a soft brush. If highlights have not cleared due to over exposure you can add a small amount of ammonia to the wash water. However, this will make the hardened casein soft and fragile.