The Autochrome is a direct positive (additive) colour photography process invented by the Lumière brothers in 1903. Autochrome plates were created by coating a sheet of glass with microscopic potato starch grains dyed red, green, and blue. These formed a screen of color particles. Carbon or lamp black was applied over the plate, filling in the spaces around the starch grains. Then a (panchromatic) silver gelatin emulsion was applied over the color screen. When the plate was exposed, the base side was turned toward the subject being photographed, and the color screen acted as a filter over the emulsion. The as B&W reversal developed plate rendered a positive color image with delicate color qualities.

Recipes and processes The original Autochrome process according to The Metropolitan Museum of Art

Autochrome starch grains were in the range of 10 to 20 microns in diameter. Resolution of the image is not critical for the present experiment. A separation by flotation will be done to avoid larger grains2.

Fill a large container with 2 liters of distilled water and 75 grams of potato starch.

Stir vigorously. Allow it to set for 15 minutes. The majority of grains are deposited in the bottom, while the smaller particles remain in suspension. Using a plastic tube, siphon the intermediate layer as best as possible (avoiding being to close to the top or the bottom).

Filter this solution using a Büchner funnel covered with filter paper, recovering a few grams of starch grains. Rinse these in ethanol and air dry.

After dry, gently pestle the grains in a mortar to separate lumps.

Dilution of the dyes in distilled water will be done according to original dilutions in autochrome plates:

Orange-red grains:

• Distilled water 100 ml
• Erythrosine 14,5 g
• Rose Bengal 2,6 g
• Tartrazine 19,7 g

Green grains:

• Distilled water - 100 ml
• Ammonia - 9 g
• Tartrazine - 21 g
• Patent Blue - 10 g
• Sodium Sulfate - 21 g

Violet-blue grains:

• Distilled water - 100 ml
• Crystal Violet - 7 g
• Malachite Green - 1 g

Tartrazine was used in different concentrations both in the orange-red (19,7g) and in the green grains (21g); the concentration for this experiment will therefore be the approximate average - 20g.

In the case of the dyes present in the green dye (tartrazine and the patent blue) ammonia and sodium sulfate are added so the ionic environment provided by the starch would adsorb the colors.

Tinting

The selected starch grains are mixed to its mass equivalent in dye-saturated solution.

The solutions so far are:

1.

• 100 ml water
• Erythrosine 14,5 g

2.

• 100 ml water
• Rose Bengal 2,6 g

3.

• 100 ml water
• Tartrazine - 20 g
• Ammonia - 9 g
• Sodium Sulfate - 21 g

4.

• 100 ml water
• Patent Blue - 10 mg
• Ammonia - 9 g
• Sodium Sulfate - 21 g

5.

• 100 ml water
• Crystal Violet - 7 g

6.

• 100 ml water
• Malachite Green - 1 g

The ratio in the original recipe was of starch to dye is:

• 2,3g dye to 3g starch for the orange (Erythrosine, Rose Bengal, Tartrazine)
• 2,24g to 3g starch for the green (Patent Blue, Tartrazine)
• 2,25g dye to 3 g starch for the blue-violet (Crystal Violet, Malachite Green)

In the present experiment the dyes are individually added to the starch. The ratio will be maintained as above, except for Tartrazine of which an average value will be used (2,27g).

Stir the mix for 30 minutes to one hour until there are no white starch grains. This is done at room temperature, except for Crystal Violet and Malachite Green which need to be at 30°C using a double-boiler. Strain the solution through Whatman filter paper and air dry.

First varnish:

• Toluene - 100 g (87 ml)
• Natural rubber - 1,5 g

Dissolve the rubber in toluene for 24 hours.

Add:

5,6 ml of the 10% solution of dammar residue in toluene (see second varnish) - this solution is obtained from the mixture described in the second varnish (ethyl acetate and dammar) after rinsing with 60ml of ether and let dry. Make a 10% solution in toluene3.

Second varnish: 4

In a container, add:

• Ethyl acetate 300 ml
• Dammar gum 28,8 g

Let dissolve for 24 hours, stirring occasionally. An insoluble residue is left in the bottom. Recover this residue using filter paper. Use the residue for first varnish.

Add to the filtered solution:

• 7,2g nitrocellulose

Stir until complete dissolution (few days) and add:

• Castor oil 4,536 g

Strain using filter paper.

Information on dyes used for the experiment

1.

• CI #: 19140
• Name: Tartrazine
• Family: Azo
• Other Names: Acid Yellow 23
• CAS#: 1934-21-0
• Supplier: Fluka/ Sigma-Aldrich
• Name given by supplier: Tartrazine
• Solubility: 0.5gr/ 10ml*

2.

• CI #: 42025
• Name: Malachite Green Ortho-chlorinated
• Family: Triarylmethane
• Other Names: Setoglaucin, Basic Blue 1
• CAS#: None
• Supplier: Salor/ Sigma-Aldrich
• Name given by supplier: Rhoduline Blue 6G
• Solubility: No known value*

3.

• CI #: 42051
• Name: Patent Blue
• Family: Triarylmethane
• Other Names: Acid Blue 3
• CAS#: 3536-49-0
• Supplier: Fluka/ Sigma-Aldrich
• Name given by supplier: Patent Blue V calcium salt
• Solubility: Water soluble*

4.

• CI #: 42555
• Name: Crystal Violet
• Family: Triarylmethane
• Other Names: Basic Violet 3
• CAS#: 548-62-9
• Supplier: SIAL/ Sigma-Aldrich
• Name given by supplier: Crystal Violet
• Solubility: 0.01-0.1gram/ 100 ml at 15.5°C*

5.

• CI #: 45430
• Name: Erythrosine
• Family: Xanthene
• Other Names: Acid Red 51
• CAS#: 568-63-8
• Supplier: National Aniline & Chemical Co.
• Name given by supplier: Erythrosin, Bluish (Iodin Eosin)

6.

• CI #: 45440
• Name: Rose Bengal
• Family: Xanthene
• Other Names: Acid Red 94
• CAS#: 632-69-9
• Supplier: Aldrich/ Sigma-Aldrich
• Name given by supplier: Rose Bengal
• Solubility: 100mg/ ml*

*Data provided by Sigma-Aldrich technical services based on their experiments.

* Tartrazine was used both in the red-orange and the green grains

The Autochrome dyed grains mixing ratios from 1930.

ratio mass of starch in mg/ for solution in mg :

• for orange grains 1.3
• for green grains 1.34
• for blue-violet grains1.33