The Darkroom: Page Contents...

A Special Note About Potassium Cyanide Use:
Material Safety Data Sheets (MSD):
Standard Lab Practice:
Standard Plate Dimensions:
Collodion Optics:
A Basic Collodion Formula:
Developers for Collodion:
The Collodion Calculator:

 A Special Note About Potassium Cyanide Use:

Before we go any further...If you're one who still insists on using Potassium Cyanide as a fixing agent for collodion films, please recognize the hazards involved. This stuff is deadly. The following is an excerpt from an AMES research safety document regarding Potassium Cyanide. The term LD50 references the Lethal Dose required to produce a 50% death rate in a test population (in this case rats).

Potassium Cyanide Health Effects:

Acute toxicity is high.
Ingestion of NaCN or KCN or exposure to their salts or their aqueous solutions by eye or skin contact can be fatal.

Exposure to as little as 50-150 milligrams can cause immediate collapse and death.

Symptoms of nonlethal exposure to cyanide include weakness, headache, dizziness, rapid breathing, nausea, and vomiting.

Cyanide salts are corrosive and toxic.

Decomposition products of HCN and nitrogen oxides are extremely hazardous.

LD50 (Lethal Dose for 50% of test subjects) is:
KCN (potassium cyanide), 8.5mg/kg (of body weight), orally injested – rat
NaCN (sodium cyanide), 6.4 mg/kg (of body weight), orally injested – rat

The above excerpt refers to "decomposition products of HCN...". HCN is hydrogen cyanide GAS. This is released if potassium cyanide comes in contact with acids (among other things). Remember that your developers use acids as restraining agents... mixing developers and potassium cyanide is a recipe for trouble.

Hypo (sodium thiosulphate) is an equally effective alternative for removing undeveloped silver salts from the film and involves none of the hazards.
Please be safe. There is no reason whatsoever to use Potassium Cyanide.

Now, on with the show...

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 Material Safety Data Sheets:

This is where the rubber meets the road, as it were.
The place where science, chemistry in particular, plays a predominant role in the artistic process. Because the darkroom, and to an even greater degree the wet-plate collodion darkroom, is essentially a chemistry lab, there are a number of "good practice" techniques and safety habits that one should be familiar with.

Because the wet-plate lab deals with a wide variety of potentially hazardous materials, the first order of business is to learn about the materials, their hazards, and how to handle them safely. Several chemicals used in the process are poisonous, carcinogenic, extremely flamible, and/or potentially explosive.

Read and understand the MSD sheets for the particular chemicals you have in your darkroom, and seek counsel from trained professionals (chemists, hazardous material handlers, specialized public safety officers, etc.) who are familiar with proper handling and disposal of these chemicals.


Silver NitrateView complete MSDS
Nitric AcidView complete MSDS
Ether View complete MSDS
Cadimum BromideView complete MSDS
Potassium CyanideView complete MSDS
Potassium IodideView complete MSDS
Ammonium IodideView complete MSDS
Ferrous SulphateView complete MSDS
Acetic AcidView complete MSDS
Ethyl AlcoholView complete MSDS
Potassium BromideView complete MSDS
Gallic AcidView complete MSDS

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 Standard Lab Practices

Safety Equipment

Safety glasses/goggles
Always, always, always wear safety glasses or goggles when working with chemicals of any kind. You are a photographer. Your eyesight is crucial to the work you do (not to mention just getting around in your daily life). Don't take chances. Wet chemistry can splash and/or spill, and chemical dust can become airborne. Silver nitrate in particular, will permanently stain organic materials (think skin and eyes!) when it comes in contact with them. If you get it in your eyes, it will blind you. Why take chances?

Nitrile gloves are a good idea whenever you are working in the collodion darkroom. Remember, your skin is porous and you can can absorb many of the chemicals you are working with into your blood stream through your hands. It's not that inconvenient to slip on a pair of gloves. It's a good habit to get into, and at the very least will keep your fingers and nails from picking up silver stains.

Though, not absolutely necessary for all operations, it's not a bad idea to use a respirator when handling dry chemistry that is powdery and can easily become airborne.

Measuring Liquids
For large volumes, pour the liquid into a graduated cylinder then raise the cylinder to eye level to view the surface of the liquid (not the miniscus at the edge of the cylinder) to get an accurate reading of the volume.

For measuring smaller volumes, a graduated syringe provides the most convenient method. Plastic syringes are cheap and relatively easy to get, and an indispensable item to have in your darkroom. To measure out and dispense small amounts of liquid, press the syringe plunger all the way forward, then dip the tip of the syringe in the liquid to be measured and draw back on the plunger until the plunger position is at the appropriate value on the graduated scale.

Weighing Solids
There are a variety of pocket sized digital scales available at very affordable prices. This is another must have for the darkroom. When ever using a scale, always cover the weighing pan with a square of waxed paper. Tare (or zero) the scale after placing the waxed paper on the pan, then place the dry chemicals on the paper to weigh them. The paper keeps the scale clean, and also makes it much easier to move the chemicals from the pan to the beaker that contains the solvent.

Calculating Concentrations
When purchasing chemicals in solution, quite often their concentrations are given in the form of Molar concentrations. To understand what this is, let's begin with a particular chemical compound, such as Silver Nitrate, which is composed of three elements, Silver, Oxygen, and Nitrogen, bonded in a very specific way. Each element has a very specific weight which can be found on a periodic table of the elements. This is called the element's atomic weight, and although that's true, the number presented is actually the weight of one Mole (6.02 x 10e23 atoms) of the element measured in grams.

The short of the story is, if we know the chemical formula, in this case AgN03 we know we have one silver at 107.86 grams/Mole, one nitrogen at 14.006 grams/Mole, and three oxygen at 15.9994 grams/mole. Add them all up and you have the formula weight for one Mole of Silver Nitrate at 169.873 grams. A silver nitrate bath for sensitizing collodion is typically 0.4866M, or 0.4866 Moles of silver nitrate per liter of water. To convert this to the number of grams of Silver Nitrate needed, simply multiply the Molar concentration by the formula weight of Silver Nitrate, and the result is the number of grams of Silver Nitrate, that was dissolved in one liter of the solvent (in this case water). Crunching the numbers gives us 0.4866 Moles/liter * 169.873 grams/Mole = 82.66 grams/liter.

A more "cook book" form of listing chemical concentrations may be found in many "recipe" style books that call for a certain number of grams of a compound to be dissolved in a particular volume of solvent, usually distilled water. In this case, changing the total volume to suit your needs is simply a matter of proportions.

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 Standard Glass Plate Dimensions

Traditional dimensions for glass plate collodion work are:

Whole Plate:6.5" x 8.5"
Half Plate:4.25" x 5.5"
Quarter Plate:3.25" x 4.25"
1/6th Plate:2.5" x 3"
1/9th Plate:2" x 2.5"
1/16th Plate:1.625" x 2.125"
Gem:0.5" x 1"

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 Collodion Optics

The spectral sensitivity of collodion is markedly different than what the eye sees. The image on the left is a photograph of a solar spectrum captured on collodion. A color image of the visible part of the same spectrum was also taken and overlayed on the black and white image for reference. Note that the film's sensitivity extends far beyond the visible blue, into the region of ultraviolet (UV). Also note that the lower end of collodion's sensitivity begins to drop off in the middle of the visible spectrum, around blue/green. Thus, colors below green (i.e. yellow, orange, and red) will not trigger an actinic response in the film, thereby leaving those regions of an image containing these colors, black. Conversely, those regions of a scene that are highly reflective in ultraviolet will appear bright white in a collodion photograph even though they may appear dark to our own eyes in the original scene.

Okay, if you've been paying attention, you'll say..."but what about that bowl of red cherries I photographed? They're not completely black. What's up?" Well, what the collodion is seeing there is the reflection of UV light from the surface of the object. The object has color, yes, but it is also reflecting UV from it's surface, which is what the film sees.

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 A Basic Collodion Formula

Here is a good general purpose collodion formula for making ambrotypes or negatives. The total volume is 12 ounces.

In a 16 ounce bottle, Pour:
150 ml USP standard collodion
100 ml Ethyl Ether
As you pour the ether into the collodion, you will notice a cloudy layer form on the top of the collodion. Not to worry, this will dissolve as we proceed.

In a 50 ml beaker, dissolve
3 ml Distilled Water
1.9 gm Cadmium Bromide (For negatives, use 1.3 gm Cadmium Bromide)
The cadmium bromide is generally clumpy and hard and will take a little time to completely dissolve. Gently heat the solution on a hot plate while constantly swirling the liquid in the beaker to speed the process along. Pour this solution into the collodion, cap the bottle and shake vigorously. Rinse the 50 ml beaker with distilled water and dry.

In a 250 ml beaker, pour
100 ml Ethyl Alcohol (190 proof)

In a 50 ml beaker, dissolve
3 ml Distilled Water
2.6 gm Potassium Iodide (For negatives, substitute 3.2 gm Ammonium Iodide)
Swirl the liquid in the beaker until completely dissolved. Pour this solution into the alcohol and swirl gently until mixed.

Pour the alcohol mixture into the collodion a little at a time, capping and shaking the collodion after each addition.

When done, cap the collodion bottle and allow to set undisturbed for a week.

At normal room temperatures, the collodion will last 6 or 7 months. As it ages, the color will change from nearly clear, to straw yellow, and eventually to redder hues as shown in the illustration where collodion "A" is 1 week old and collodion "B" is 7 months old. As it ages, it may also begin to loose sensitivity, and exposure times may increase. This color change is due to free iodine being released into the collodion from the potassium iodide.

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 A Collodion Developer

Here is a good general purpose ferrous sulfate developer for collodion. (and it's easy to remember!) The total volume is approximately 7.5 ounces.

In an 500 ml beaker, Pour:
210 mlDistilled Water
10 gmFerrous Sulfate
Stir the Ferrous Sulfate into the distilled water until it's completely dissolved, then add:
10 mlAcetic Acid
10 mlAlcohol
Mix thoroughly, and filter the solution into an 8 ounce bottle.

To better understand what the developer is actually doing and to make the recipe a little less mysterious, let's look at the function of each component individually and see what it does.

The first ingredient is water. This is merely the solvent which allows the various chemicals to blend and provides a measure of dilution.

Next on the list is Ferrous Sulfate. This alone, is the developing (or reducing) agent. It acts to reduce the exposed metallic salts (silver iodide) into metallic silver. Ferrous sulfate is an aggressive developer, and by itself, without dilution or restraining, would begin reducing silver salts that had not been exposed by the image forming light, thus resulting in a fogged plate.

The action of the developer can be restrained by the addition of an acid. The usual choice for this is acetic acid, although other acids (such as Nitric Acid which tends to brighten the surface of the metallic silver deposits) can also be used. Although if the amount of silver iodide in the collodion is too little, or if insufficient silver nitrate is present on the plate at the time of development, the use of nitric acid may prevent the deposition of metallic silver in various regions of the plate.

Another commonly used restraining agent is sugar. When dissolved into the developer, the sugar acts to thicken the fluid slightly, making it more viscous and thus slowing the physical agitation of the developer on the plate, slowing the rate at which the developer comes in contact with the exposed silver salts.

Alcohol can be also be added to the developer as necessary to act as a "wetting agent" if it is found that the developer has an oily appearance when poured onto the surface of the plate.

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 Collodion Calculator

Collodion Calculator

Type in the total collodion volume desired,then click the calculate button
ml Total Volume

Bromo-Iodizing Formulas for Collodion, 5%, USP

. Ommeganck
Ambrotype Ambrotype
Total Volume: 500 ml 500 ml 500 ml 500 ml 500 ml 500 ml 500 ml 500 ml 500 ml
Collodion 110 ml 110 ml 215 ml 100 ml 100 ml 95 ml 95 ml 75 ml 85 ml
Ether 270 ml 270 ml 140 ml 240 ml 240 ml 195 ml 195 ml 260 ml 200 ml
Alcohol 120 ml 120 ml 140 ml 160 ml 160 ml 210 ml 210 ml 165 ml 215 ml
Distilled Water 4 ml 4 ml 4 ml 4 ml 4 ml 4 ml 4 ml 4 ml 4 ml
Ammonium Bromide . . . 0.23 gm 0.38 gm 0.38 gm 0.19 gm 0.19 gm .
Ammonium Iodide 2.24 gm . . 2.26 gm 1.88 gm 1.90 gm 1.90 gm 1.88 gm .
Cadmium Bromide 1.12 gm 1.12 gm 2.73 gm 0.15 gm . 0.38 gm . 0.08 gm .
Cadmium Iodide 2.24 gm 2.24 gm . 1.50 gm . 1.90 gm . 1.13 gm 3.80 gm
Iodine . . . 0.19 gm 0.19 gm 0.19 gm 0.19 gm 0.08 gm 0.08 gm
Potassium Bromide . . . . 0.38 gm . 0.19 gm . .
Potassium Iodide . . 3.64 gm . 1.88 gm . 1.90 gm . .
Zinc Iodide . 2.24 gm . . . . . . .

The formulas above were interpreted from data contained in The Silver Sunbeam, and converted to be used with standardized pyroxyline solutions. Enter the total volume of iodized collodion needed in the text box, then click on the 'calculate' button. Find the column that corresponds to the type of Bromo-iodizing solution appropriate for your application, then read vertically downward to determine the type and amount of chemistry required.

Mixing of the chemistry is generally done as follows: Pour the collodion into a bottle large enough to contain the total volume of chemistry. Pour the ether into the collodion. Cap the bottle and set aside. Pour the water into a small beaker or shot glass. Weigh out the appropriate dry chemistry and place this into the water. Stir this mixture with a glass rod, carefully crushing the solid pieces, until it is completely dissolved. Pour this into the alcohol and stir until it is completely dissolved. Finally, pour the alcohol mixture into the collodion a little at a time, shaking the collodion between additions to thoroughly mix the solutions.

Avoid mixing chemistry near open flames due to the extremely flamable nature of the alcohol, ether, collodion, and their vapors.

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