Tips and Techniques

Page Contents:
A Special Note About Potassium Cyanide Use:
Material Safety Data Sheets (MSD):
Standard Lab Practice:
Standard Plate Dimensions:
Film Holders:
Collodion Optics:
A Basic Collodion Formula:
Developers for Collodion:
Plate Prep: Tin
Plate Prep: Glass
Pouring Collodion:
Sensitizing the Plate:
Making Your First Exposure:
Developing the Plate:
Fixing the Plate:
Varnishing the Plate:
Using a Light Meter:
Troubleshooting Peeling:
Troubleshooting Comets:
Troubleshooting Developing:

A Special Note About Fixers and Potassium Cyanide Use:

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

Before we go any further...If you're one who still insists on using Potassium Cyanide instead of Hypo 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.

In closing, please consider using Hypo for fixing your plates. It's a tried and true method with minimal risks.

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 flammable, 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 Nitrate:View complete MSDS
Nitric Acid View complete MSDS
Ether View complete MSDS
Cadimum Bromide View complete MSDS
Potassium Cyanide View complete MSDS
Potassium Iodide View complete MSDS
Ammonium Iodide View complete MSDS
Ferrous Sulphate View complete MSDS
Acetic Acid View complete MSDS
Ethyl Alcohol View complete MSDS
Potassium Bromide View complete MSDS
Gallic Acid View complete MSDS

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Standard Lab Practices

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 meniscus 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.

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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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Film Holders

Most modern view cameras use a standardized cut (sheet) film holder. These are designed to hold two sheets of film, one on each side of the holder. These standardized sheet film holders must be modified by removing a portion of the septum that separates the front and back sides of the film holder before using them to shoot tintypes or glass negatives. The size of the opening in the septum determines the size of the plate that can then be used with that film holder. To keep the plate from falling completely through the opening in the septum, supporting wires are then placed across each corner of the opening to hold the sensitized surface of the plate at the same location as the original sheet film.

When loading a sensitized plate into the modified sheet film holder, begin by removing the rear dark slide (We mark the front of our modified film holders with a label indicating "This Side Toward Lens". Leave the front dark slide in the film holder). Lay the modified film holder on a bench top with the open side facing up. Next, lay the surface of the plate that has been coated with collodion into the septum opening so that the collodion surface rests on the supporting wires. (collodion side down) Place a small plastic spring, which can be a folded strip of soda bottle plastic, or anything similar, onto the back of the plate. Hold this spring in place with a finger while sliding the dark slide into position over the rear of the plate. This dark slide holds the spring in place and keeps the plate from falling backward when the film holder is handled and while loading and unloading it in the view camera.

Because this method of holding a sensitized plate in the film holder places the sensitized photographic surface at the focal plane, the thickness of the plate is of no consequence. You can use a film holder modified in this manner to shoot tintypes or glass negatives of any thickness as long as they will fit beneath the rear dark slide.

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Collodion Optics
Collodion Spectrum Color image of still life
Panchromatic b/w image of still life Collodion image of still life

The spectral sensitivity of collodion is markedly different than what the eye sees. The upper left image is an actual 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.

To illustrate this, a color photo was taken (upper right) of a still life. The same image is presented as a panchromatic black and white image (lower left), and finally as a collodion photograph (bottom right). Pay particular attention to the greens, yellows, and reds, which all appear dark in the collodion image. And note the blue and white patterned fabric in the foreground which appears to be entirely white without pattern at all in the collodion image.

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's recorded by the film.

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A Basic Collodion Formula

Here is a good general purpose collodion formula for making ambrotypes or negatives. The total volume about 600 ml.

Stock (unsalted) Collodion
In a 32 ounce bottle, pour:
250 ml USP standard collodion
In a 500ml beaker, measure out:
170 ml Ethyl Ether
150 ml Ethyl Alcohol
Then pour the ether/alcohol mixture into the bottle containing the collodion and cap.
Stock Sensitizer
In a 50 ml beaker, place:
4 gm Potassium Iodide
3 gm Cadmium Bromide
Dissolve this with 8ml distilled water. When completely dissolved, add
17 ml Ethyl Alcohol
Pour the sensitizer from the beaker into a 1 oz bottle and cap

The cadmium bromide is generally clumpy and hard and will take a little time to completely dissolve. If necessary, gently heat the solution on a hot plate while constantly swirling the liquid in the beaker to speed the process along.

A few days prior to shooting, combine the sensitizer with the stock collodion, swirl the liquid in the bottle to mix. Allow the salted collodion to rest undisturbed for a day or two before using to allow bubbles to escape, sediment to settle, and the collodion to ripen.

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. This color change is due to free iodine being released into the collodion from the potassium iodide. As it continues to age (1 year and longer), the salted collodion's sensitivity will decrease, it will exhibit higher image contrast, and become physically fragile making the surface extremely easy to damage.

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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, thereby slowing the rate at which the developer comes in contact with the exposed silver salts. If you'd like to see this in action, the next time you make a cup of hot tea, make two, one with sugar already dissolved in the water before inserting the tea bag, and the other with just water alone. You'll notice the tea using water alone colors up quicker than that which had the sugar dissolved in it.

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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Plate Prep for Tin

The first thing to keep in mind regarding collodion photography is that as much as we'd all like it to be as fool proof and reliable as buying a roll of film from the photo shop, it just isn't. Precoated aluminum is made to suit industrial and architectural applications - NOT photography. As photographers, we've just commandeered its use for tin typing because it's fast, convenient, and easy to use. Your alternative is to invest the time, energy, and effort into japanning your own plates, or shoot ambrotypes on glass (which are beautiful in their own right, but also come with their own set of technical problems!)

Precoated tin is covered with a protective layer of static cling plastic, not unlike plastic wrap found in your kitchen drawer. Because it's held in place by static electricity, there are no adhesives or any other chemicals to contaminate the coating. You may see mottled marks on the surface of the plate when you remove the protective covering, but this will have no effect on the development of your image.

In spite of the fact that precoated tin is not designed for use with photography, it does work exceedingly well over 99% of the time. However, you may occasionally encounter a "regular" pattern of streaks or spots in a developed image that are aligned along one axis of the plate.The patterned appearance of this type of artifact makes it quite different than most other artifacts encountered in the collodion process which tend to have irregular or smooth boundaries. This type of artifact is the result of over development. Refer to our trouble shooting section for more information on how to avoid this type of artifact.

Over development also causes a host of other image problems (increased grain and general muddiness in the shadow areas are the most noticeable) and should be avoided. Always keep your development times to an absolute minimum.

Another thing to keep in mind, is that even if you've made an image on tin and you don't like it for whatever reason, it's an easy matter to wipe the plate down with a blend of alcohol & ether to remove the image and coat the plate again.

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Plate Prep for Glass

Glass plates of various colors can be purchased from a variety of stained glass outlets. When purchasing glass, be sure to ask for "Float" glass. Unlike much of the glass used in stained glass applications, this type of glass has a smooth surface. For starters, and to keep things simple, you can purchase ordinary plate glass at your local hardware store to make your images. Once you have it cut to properly fit your plate holder, be sure to sand or "file" the edges. For this, one can use sandpaper or more conveniently a sharpening stone. Both serve the same purpose but the sharpening stone will last forever, is easier to handle, and is less messy. Keep the sharpening stone or sandpaper wet while filing the edges of the plate. This keeps the glass dust from blowing around in the air, getting on everything else, and being inhaled. Gently file all edges (both sides) of the glass plate to remove the sharpness. Be careful not to strike the plate with the sharpening stone as this might chip the glass or crack it. The purpose of filing the edges serves two purposes. First, it will make it less likely that you'll accidentally cut yourself later on, and secondly, it helps keep the collodion away from the very edge of the plate which helps prevent the collodion from catching and peeling.

When you've filed all the edges, wipe down the edges with a cloth or rinse with water to get rid of the excess glass dust from filing. Place the plate in a wooden vise, tighten the vise just enough to firmly hold the plate, and then pour a mixture of whiting (calcium carbonate, which is similar to chalk dust. This can be found in most stained glass supply stores) and alcohol. Use enough whiting to make a thin slurry that looks milky when poured onto a plate. Pour the whiting mixture onto the surface of the glass plate and then rub firmly and vigorously in small circular motions, covering the entire plate. Continue for a couple of minutes. Pay attention to the edge of the plate, they often get over looked and get less scrubbing time than the center of the plate. Wipe the surface dry with a clean dry flannel. Flip the plate over and repeat on the opposite side. When done, remove the plate from the vise and wipe down the edges of the glass to remove any excess whiting that may have collected there (this keeps the chalk dust from contaminating your silver nitrate bath later on).

Before moving on to the next step (which is coating the plate), make sure your camera is set up, your shot composed, and your exposure calculated. Once the collodion is poured on the plate, you have a limited amount of time with which to work before the collodion dries out and is no longer usable. The practical working time depends on the temperature and humidity of the day. Generally, 75 F degrees and 40% humidity will give you approximately 10 or 15 minutes of working time. Experience will tell you how long you have to work under the conditions in your area.

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Pouring Collodion

Handle your collodion gently. Don't shake it, and pour it gently and slowly. Never worry about getting the last drops out of the bottom of the bottle. Collodion is constantly throwing down chemistry as it ages and this all settles out on the bottom. Using the dredges will result in pinholes throughout your image. Now that the warnings are out of the way...

To coat the plate, hold it at one corner using your index and middle fingers to support it from below, while your thumb holds the very corner of the glass from the top side.

Hold the plate precisely level. Pour the collodion slowly but steadily onto the center of the plate. As you pour the collodion, it will form a circular pool in the middle of the plate. Adjust the tilt of the plate as necessary to maintain the circular shape until enough collodion has been poured to amply cover the plate. Remember, work slowly and methodically. You have more time to coat the plate than what you think, so take your time. You will also need to pour more collodion onto the plate than you think you'll need, so be generous. Remember, you can always drain off any excess after the plate is coated.

When flowing the collodion over the plate, plan ahead. It doesn't matter whether you move it in a clockwise or counterclockwise direction, or from which corner you pour back into the bottle. As long as you work in a consistent fashion, you'll be okay. For the sake of illustration, let's assume we are holding the plate with the left hand. We'll begin by flowing the collodion into the near left corner, then move clockwise from there to the far left, then the far right, finally pouring off into the collodion bottle at the near right corner. When I mention tipping the plate, don't physically tip the plate as much as "Think" about tipping the glass. It doesn't take much!

Here we go: Once enough collodion has been poured onto the plate, gently tip the glass toward the left and a little bit toward you. The collodion will gradually begin to flow to the near left corner.

As it approaches the edge of the glass gently tip the plate away from you until the collodion approaches the far left corner.

Then gently tip the glass to right so the collodion moves into the far right corner.

And finally tip the plate toward you slightly to drain the excess collodion off the corner of the plate and back into your collodion bottle. Don't hurry the collodion or try to force it back into the bottle. This will usually result in spills off the edge of the plate. Just keep everything flowing at a constant rate and you'll be a pro in no time.

Some general precautions when flowing the plate: Always keep the collodion moving outward from the center pour. Don't try to tip the plate backwards to "coat a spot you might have missed". This will inevitably leave a thick ridge as it builds up on the collodion that has already dried to some extent. Once you begin draining the collodion back into the bottle, begin rocking the plate from side to side to prevent ripples from forming on the surface of the collodion. (These ripples will show up in your image later if you don't take care of them now!)

When the collodion stops draining from the plate, raise the plate and cap the bottle. Continue rocking the plate slowly from landscape orientation to portrait orientation (about 1 or 2 seconds per rotation) while always keeping the draining point at the bottom. Continue rocking until the collodion becomes firm, but not dry. You can tell when it's ready by gently touching the collodion at the draining corner, when your finger leaves a dent without feeling wet or slipery, it's ready.

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Sensitizing the Plate

Dip the newly coated plate into the silver nitrate bath. Do this with confidence, lowering it smoothly and evenly into the tank. This should only take 2 or 3 seconds to accomplish. Don't splash or disturb the solution any more than absolutely necessary and don't hesitate while inserting the plate into the liquid. Hesitation can cause lines in the image later on. Once the plate is in the silver nitrate, close the lid of the tank and wait approximately 2 minutes.

While the plate is in the sensitizer, this is a good time to prepare your materials for development. Set out a tray large enough for your plate, a beaker or wide mouth jar of distilled water to stop the development, and a small beaker (50ml) or shot glass to hold the developer. Pour out a sufficient amount of developer to cover the glass plate (for example a 7x9 inch plate would require about 10 ml of developer).

After approximately 2 minutes, pull the plate from the liquid in the same confident manner in which it was inserted. Again, avoid hesitation. Look at the surface of the plate as you're pulling it out. If you see an oily appearance with rivulets running off, the plate needs to be reinserted into the silver nitrate. If the silver nitrate flows smoothly off the surface when it's removed from the tank, it's ready for the plate holder.

Blot the excess silver nitrate from the edges of the plate by placing a clean dry paper towel on the darkroom bench, and setting the edge of the plate on the towel. Rock the plate forward and back slightly, then repeat the procedure on the other edges as necessary. Insert the plate in the holder with the collodion side toward the dark slide (usually down). Gently wipe the back of the plate with a dry towel to remove any excess silver. Close the plate holder.

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Making Your First Exposure

A simple test exposure can be made by using the dark slide of the plate holder. Start out by exposing the entire plate for a base amount of time (this depends upon the lighting conditions and the f/stop used. For f/8 in open shade, try starting with 3 seconds). After the base exposure, push the dark slide 1/4 of the way closed and expose again for one base exposure. Push the dark slide in 1/2 of the way closed and expose again for two base exposures. Finally slide the dark slide in 3/4 of the way and expose again for four base exposures. This will give you total exposures on the collodion of 1x, 2x, 4x, and 8x the base exposure. In other words, 4 exposures separated by one-stop intervals.

Develop and fix the plate as you would normally and inspect the image for the appropriate exposure range. This is a great technique if you're just starting out, using a camera you're unfamiliar with, trying out a new lens, or working in unfamiliar lighting conditions.

Dark slide full open.
Expose Plate 1X Base Exposure
(Total exposure on plate = 1x Base)
Push dark slide 1/4 way in.
Expose Plate 1X Base Exposure
(Total exposure on plate = 2x Base or +1 stop)
Push dark slide 1/2 way in.
Expose Plate 2X Base Exposure
(Total exposure on plate = 4x Base or +2 stop)
Push dark slide 3/4 way in.
Expose Plate 4X Base Exposure
(Total exposure on plate = 8x Base or +3 stop)

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Developing the Plate

Development can be done in a tray or by applying the developer directly to the hand held plate. Development of collodion requires free sliver nitrate to be on the surface of the plate, thus it is important to flow the developer evenly over the surface of the plate from one side without causing turbulence that would wash the silver off the plate. Pouring directly onto the plate surface from above will prevent full development where the developer first impacts the plate, producing thin images at that location. Properly flowing developer onto a hand held plate takes a little practice, but is worth the effort because it allows you to observe the progress of development and to stop the development without delay.

Bring the newly exposed plate into the darkroom and remove the plate from the holder. Hold the plate with the collodion side up, in one hand above an oversized tray (the tray is there to catch the spills). Position yourself so that you can see a glare from the safe light on the surface of the glass. This will help you determine how the developer flows onto the plate. In the other hand hold the small beaker of developer over the edge of the plate near the far corner. Tip the plate away from the beaker so that the developer will run down the plate in a wave toward the hand holding the plate. Pour the developer by drawing the beaker long the side of the plate, continually pouring along the length. Tip the plate as necessary to keep the developer flowing evenly across the plate. Watch for areas that the developer might miss (dry spots) and move the plate quickly as necessary to try and force the developer to cover these areas. Continue moving the plate, agitating the liquid on the surface until the image begins to form. When the image is properly formed (mid tones formed with shadow areas remaining clear) pour distilled water onto the plate to wash off the developer and excess silver. When the plate is thoroughly washed, the water will sheet smoothly off the surface. If the plate looks oily, continue washing. Once the developer and excess silver nitrate are washed from the surface, the plate can be viewed in daylight. At this point, the plate is ready for fixing.

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Fixing the Plate

After the plate is developed, you'll see a dark image on milky background. This milky background is the remaining undeveloped silver halides. If not removed from the collodion, these halides will eventually become dark silver metal, permanantly staining, or even obliterating the original image. By themselves, these silver halides are not soluable in water. The function of the fixer is to combine with these silver halides making a water soluable compound that can then be rinsed out of the collodion with fresh water.

There are several chemicals available that will do this job. Hypo (sodium thiosulfate) and Rapid Fix (ammonium thiosulfate) are two of the most commonly used. Fixing the plate can be done in either a tank or in a tray with equally effective results.

Once you place the plate in the fixing bath, you'll begin to see the milky background slowly dissolve away. The rate at which the milkyness disappears depends on the concentration and freshness of the fixing bath. A good rule of thumb for gauging when the fixer bath is exhausted and should be replaced is by making note of the time it takes a plate to visually clear with a fresh bath. When this time becomes approximately twice the original clearing time, it's time to mix up a fresh batch of fixer.

Another good rule of thumb for proper plate fixing times is to note the time it takes for the plate to clear visually, then double this time before removing the plate from the fixing bath. Fixing for periods of time longer than this may allow the collodion film to absorb more of the fixing chemistry, making it more difficult to remove during the wash step. Or the fixer may begin to etch the silver metal away that forms the image itself.

Wash the fixed plates in fresh running water for a minimum of 5 minutes (10 to 20 is better) to remove what chemistry remains in the collodion film.

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Varnishing the Plate

The traditional method of finishing a plate is to varnish it after it's thoroughly dry. This is done by carefully pouring a sandarac varnish over the warmed plate and drying it over a lamp or heater. It's fairly delicate work and provides all sorts of opportunities to ruin a great plate. With this in mind, always always always (did I say always?) scan your plate before you varnish it. That way you at least have a digital back up. In spite of the potential difficulties in learning the techniques of varnishing plates, it is a proven technique for sealing and preserving collodion images. It's worth the effort to master these skills.

Now, getting back to varnishing...First, pour a small amount of varnish into a pouring bottle and warm it in a beaker of water. Warm your plate over a hot plate, alcohol burner, or kerosene lamp (not hot! if you can't touch it to the underside of your wrist, it's too hot) Keep the plate moving so it heats evenly. Pour the varnish as you would pour collodion, beginning with a circular pool of varnish in the middle of your plate, then tipping the plate to the left, then away, then to the right, then finally toward you and draining the excess back into a second bottle which you will then filter again before reuse. Blot the edges of the plate on a clean paper towel, while rocking the plate toward and away from you to remove any excess buildup of varnish from the edges of the plate. Heat the plate again over an alcohol burner until the varnish has set. Place the plate in a drying rack and allow it to cure for at least 24 hours.

Now, if you're not that concerned with traditional methods, and you're feeling a little experimental, you may want to try spray polyurathane. I should offer a disclaimer here: these materials have not been tested over time, and may, or may not, cause harm to the image in years to come. There have been anecdotal reports of peeling or flaking of the collodion many years after it's been coated with paint, but I'm unaware of the details regarding the materials used in these cases. There are some differences between brands of polyurathane and the best I've seen to date is Minwax Premium Spray Polyurathane. This seems to level uniformly, provide the smoothest coat, and produce a beautifully glossy finish. As with traditional varnishing, you need to warm your plate to drive off any moisture that may be in the collodion. If you don't do this, you will see cloudy white areas show up in your image. Apply 3 or four very light coats crossing the plate in various directions. The idea here is not to leave a spray pattern in the finish.

If you're shooting clear glass ambrotypes, you have yet another method available. Black spray paint. Eeeekkkk!! Black? Yes, black. The beauty of this is, you'll be viewing your image from the glass side of the image which provides a pristine perfectly smooth and glossy surface to the front side of the image while the black paint now does double duty by sealing and protecting the collodion while it forms the black backing that you would normally mount behind the image. The advantages here are several: you no longer have to worry about the slightest bit of dust showing up in your finish, keeping a glossy texture is not important at all, and you've eliminated the air gap between the image and the black surface, thereby eliminating reflections between the glass and the background which gives you a much deeper black in the shadow areas of your image...yummmm!!! It really makes the image pop. Secondarily, you may even want to experiment with different colors of paint! If you do this, remember to stay on the dark side, since lighter tones will make your image appear as a negative. But this could be interesting too, depending on what you're looking for.

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Using a Light Meter

The first thing to note about collodion is that it is sensitive well into the ultra violet region of the spectrum; a region neither our eyes nor our visible light meters will detect. Collodion, becomes significantly less sensitive as the wavelength (color) increases and moves away from green, through yellow, orange, and finally red, a color collodion does not "see" at all.

For metering purposes, we can make the simple and reasonable assumption that the UV light intensity tracks uniformly with visible light intensity. This means that when the scene you're about to photograph gets brighter in the visible portion of the spectrum, it gets equally brighter in the UV portion of the spectrum. This is a workable assumption if you exclude metering within a couple of hours after sunrise or before sunset, when the color quality of the light is nearer to the redder, less actinic, end of the spectrum.

The second requirement for using a visible light meter to estimate collodion exposure times, is that the meter must be used as an incident light meter. Why? Because different objects in your scene will reflect different amounts of UV light, and you will be unable to predict which areas are UV bright or UV dark by viewing the scene in visible light (nor by using a visible light light-meter). For example, a navy blue fabric will appear dark on panchromatic film because it reflects little visible light, yet the same fabric appears bright in collodion images because it reflects a great deal of UV light. A reflective meter would give you erroneous readings if metering for UV exposure. Therefore this technique of using a visible lilght-meter to estimate UV exposures will only work when metering the light intensity falling on the scene (incident light meter), and not the light reflected from the scene (reflected light meter).

When putting this into practice, first determine a correct exposure by shooting a test plate. Once a good exposure is obtained on collodion, then, meter the scene and record the Exposure Index (EI) or Exposure Value (EV) that's indicated on the meter in a notebook. This will be your baseline exposure to which all subsequent exposures will be compared.

Metering after an exposure may seem quite the opposite of what you've come to expect, however, there is method to this madness! Even though the meter didn't help us with the first exposure (that's why we needed the test strip), it will help us with each subsequent exposure. Don't worry about ASA or f-stops at this point; all we're looking for are relative differences in light intensity as we move to our next scene.

When we set up the next shot under different lighting conditions, meter the scene first and record the EI. The difference between the original exposure index and the new exposure index is the number of stops difference in light intensity between the two scenes, and this is what you will use to determine your new exposure setting (f-stop and exposure time). Remember, a change of one unit on the EI scale is equivalent to a change of one f-stop, or a doubling (or halving) of the exposure time. So, if the scene brightness changed by 3 units of EI, then you know that you need to change the f-stop on your camera by 3 stops, or you need to change the exposure time by an equivalent of 3 stops (or use some combination of both that adds up to 3 stops). This method of metering will often save a great deal of guess work and bring you very close to the proper exposure on the first try.

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Troubleshooting: Collodion Peeling or Lifting from the Plate:

The "usual suspect" for collodion that peels or lifts from the plate is a plate that has been inadequately cleaned. Wear nitrile gloves when handling the plates to avoid getting finger prints and oils on the glass while handling it. Scour the plate with a slightly abrasive cleanser like Bonami, and rinse thoroughly under running water until the water sheets off smoothly without forming little rivulets on the surface of the glass. Place the plate in a rack to dry. Prior to pouring the plate, use a mixture of alcohol and whiting (powdered calcium carbonate) to scrub the plate. Finish cleaning the plate by buffing it vigorously with a clean flannel cloth. Wipe all edges to remove any whiting that may have collected there while cleaning. Pour the freshly cleaned plate and process it. If you still find the collodion is peeling or lifting from the plate, try increasing the amount of alcohol in the collodion mixture as described below.

Our second suspect is alcohol content. Generally, collodion (5% USP, as obtained commercially) is thinned for use in photography with equal parts of ether and alcohol. If the relative amounts of each solvent (ether and alcohol) are varied along a continuum from primarily ether (and very little alcohol) to primarily alcohol (and very little ether), one will find the collodion film to vary in physical character from tough and leathery to spongy and fragile. If too much ether is used, not only with the film be tough, but it will also be prone to shrinking on the order of 2.5% when it dries. This may not sound like much, but on a 10 inch plate, this is equivalent to 1/4 inch. It's this combination of shrinkage and leathery nature of the film that's responsible for the film peeling and sliding off the plate. To prevent this, it is necessary to increase the percentage of alcohol in the mixture. Begin by adding a volume of alcohol equivalent to 5% of the total collodion volume being used. Swirl the alcohol into the collodion mixture then pour and process a new plate. If peeling still occurs, add an additional 5% alcohol to the collodion and repeat. As more alcohol is added to the collodion, the film begins to lose its tough, leathery, character and becomes spongey and fragile.

When all else can apply albumen to your plate prior to coating the plate with collodion. This process isn't particularly complicated, it just takes a little time and preparation. First, to get the albumen, you have three options: separate the white from an egg, buy a carton of egg whites from the grocery store, or purchase powdered egg white and add water. Separating the white from an egg is probably the the quickest solution since eggs are relatively close at hand for most folks. The quick and dirty solution is to dip a cotton swab into the albumen and paint the perimeter of the plate, making a border about 1/4 inch wide. Let this dry completely before coating the plate with collodion. This will keep your collodion from peeling, but it will leave a darker boarder around your print where the albumen was applied. A slightly more involved procedure is to mix the egg white with water in a ratio of about 1/40. This is approximately one egg white in 1 liter of water. Mix this thoroughly and filter before use. Pour this solution onto the plate as you would pour collodion. Avoid creating bubbles or trapping dust on the plate. Allow the plate to dry thoroughly before applying the collodion. This method avoids the dark border and insures that the collodion will stick to the glass.

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Trouble Shooting - Comets:

Comets are streaks that show up on the plate that can originate from either chemical or physical causes.

One type originates at a point or grain of contamination in or on the collodion film. As the plate is dipped into the silver nitrate, this contamination is drawn away from the original point by the relative motion between the silver nitrate solution and the plate, forming the comet's swept tail.

A second, more common type of comet is the result of undissolved ferrous sulfate (from the developer) touching down on the collodion when the developer is flowed across the plate. This undissolved (concentrated) developer immediately fogs the film wherever it comes in contact. The tail extends in the direction of developer flow

To minimize the possibility of forming comets, filter your developer, and be sure to handle the collodion gently. Avoid mixing or shaking the collodion prior to use. Allow any particulate matter to settle out of the solution before using.

This is a magnified view of a comet that appears to be a physical obstruction imbedded in the collodion film. Notice the bumps sticking up above the collodion surface. This is a magnified view of a different comet that appears to be chemical in nature and one that is located within the collodion film and not distorting the surface of the film as seen in the first image. Notice the central "grain" that's resides in a very well defined region completely devoid of developed silver.

This is a magnified stereo image of a comet protruding above the collodion's surface, taken in reflected light.

This is a magnified stereo image of a comet caused by a chemical grain within the collodion film, illuminated by transmitted light.

This is the same comet as shown above, illuminated by reflected light.

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Trouble Shooting - Pouring Developer Directly onto One Spot:

Development is both a physical and chemical process. The chemical part of the process involves reducing the exposed silver iodide in the collodion film into metallic silver through the action of the developing agents. The physical aspect of the development comes into play because the presence of free silver nitrate is necessary for the chemical action to occur. An aqueous solution of free silver nitrate normally coats the surface of the plate after sensitizing it. This is the "Wet" in wet-plate. Because it's a liquid, it can easily be moved around on the plate.

The reason we use as little developer as possible during development is to keep the concentration of the free silver nitrate high enough to do it's job, and bring out an image. If, the free silver nitrate is washed away by physically "splashing" the developer onto the plate, the image won't form properly.

The most obvious way of pushing this free silver nitrate away is by pouring the developer directly onto the plate in one spot, causing the stream of developer to strike the plate with some force. This effectively pushes the free silver nitrate away from this spot, producing a somewhat circular region that has little or no image.

This image was produced by pouring the developer directly onto one spot on the plate. Artifacts like this are typically between 1/2 and 1 inch in diameter.

This is the same artifact, but the speed of the pour was much greater. Notice the extra bands surrounding the central portion. These were caused by waves and ripples as the developer "splashed" away from the center. This artifact is about 2 inches in diameter.

Errors like this, can be corrected by allowing the developer to flow as smoothly and evenly as possible across the plate.

Trouble Shooting - The Hazards of Over Development:

Exposure and development work together and one can often compensate to some degree for the other. For crisp clean images, always try to keep the development time to the absolute minimum. The longer developer is in contact with the plate, the greater the opportunity for non image forming silver to show up in the developed plate resulting in various forms of image "fog". Below is an example of extended development times and their effect on the developed image. All three images have identical exposure times but the development was progressively increased for purposes of illustration. The first image uses an appropriate development time of 15 seconds. The second image has twice the development time, and the third, three times the normal development time. Notice the increase in background "noise" showing up. In the third image, there's even a diagonal banding which corresponds to the removal of the protective plastic sheet from the tin. If you're seeing regular patterns of "noise" in your image, the solution to the problem is to increase your exposure time and reduce your development time.

Being an intermittent problem it's exceedingly difficult to troubleshoot, however, the most likely explanation regarding this patterned series of marks in the image is that it is the result of tiny regions of greater alkalinity located in the black resin coating itself. Alkalinity in these regions may produce a localized increase in the activity of the developer, causing localized fogging at these locations on the plate, resulting in this characteristic linear pattern of spots. If you encounter marks like this in your developed image, you're development times are too long. Ideally, development times should be on the order of 10 to 15 seconds with highlight areas making their first appearance in about 6 seconds. If your development times are longer than that, it's likely your exposure times are inadequate. Remember, under exposure leads to over development.

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