Preparation of the Plate
Sheets of glass are also used to make positive collodion images known as ambrotypes, as well as glass negatives from which prints can be made. The difference between the two variations depends on the density of the image. Ambrotypes are really underexposed collodion negatives that reverse their tonality when backed by a dark material or when made on dark colored glass (i.e., “ruby ambrotypes,” Figure 14). Collodion negatives and positives are virtually grainless.
First, it minimizes the hazard of cutting the skin on sharp edges of glass. (And this is particularly important to avoid if the photographer uses potassium cyanide as the fixer. Sharp or broken glass and a lethal chemical is a recipe for disaster. Additionally, if potassium cyanide is used as the fixer, it should never be stored in glass containers.) Second, the roughened edge helps adhere the collodion to the slick glass surface.
The glass used for ambrotypes or negatives must be immaculately clean in order to prevent image artifacts and peeling of the film. The glass is typically cleaned using a solution comprised of whiting or rottenstone (both varieties of fine calcium carbonate) mixed in a solution of alcohol and water. A bit of solution is poured onto the plate and rubbed around to remove oil and dirt on the glass. Care must be taken to remove all traces of this alkaline cleaning solution to prevent contamination of the expensive silver nitrate sensitizing solution. I like to use small lintless PEC Pads to clean the plates. These special pads will clean many plates before they need to be discarded.
Some collodion formulas containing cadmium bromide and/or cadmium iodide are tender and tend to lift from the surface of the plate. Adding a subbing to the surface helps prevent this defect. The most common subbing is egg albumen mixed with a small amount of water and spread about 1/8” in from the edge of the plate with a cotton swab.
Immediately before coating the glass plate with collodion, the surface should be brushed to remove ubiquitous dust.
The use of thin, chemically-resistant gloves is strongly recommended when pouring the collodion, in subsequent steps involving sensitizing the plate in silver nitrate, and additionally throughout the development process. Wetplate is historically referred to as “The Black Art” due to the silver nitrate stains that identified early practitioners. In addition to the staining potential, silver nitrate is corrosive and may cause blindness if concentrated solutions are accidentally splashed into the eyes. Because of these hazards, the use of chemically resistant gloves and protective goggles is recommended when handling this chemical.
Pouring the collodion properly is a skill that comes with some practice. Novice wetplaters have a tendency to use insufficient collodion solution in their initial pours. Too little solution causes irregular coatings and blank “islands” lacking emulsion on the finished plates. It is far better to use too much collodion and have some spill over the edge of the plate than to use too little.
Collodion has the approximate viscosity of warm maple syrup or cream and practice with such a substance can safely and inexpensively facilitate the learning process.
To pour the collodion properly, the plate is held as horizontal as possible using one of several methods. For small plates, it is probably easiest to pinch one corner between thumb and forefinger and pour the solution with the other hand. For moderate size plates, the “waiter tray” method supporting the plate from below may be best approach (Figure 16). With larger, heavier plates, a combination of one of the two previous methods while supporting the opposite corner on a table may be required.
When coating the surface should have a fairly large pancake-like pour of collodion in the center of the level plate. The plate is then gently inclined towards the photographer so that the fluid moves towards the near corner without flowing off the edge or touching the fingers holding the plate. Once the near corner is covered sufficiently, the plate is gently inclined to the adjacent nearest corner, then downward to the third corner, and finally to the “pour-off” corner. As the fluid approaches the last corner, the plate is quickly turned near vertical with the final corner placed inside a vessel used for containing the solution. The plate is rocked back and forth while the collodion drains into the collection bottle. This helps minimize lineations and irregular thicknesses in the collodion film. The entire coating operation should only take a few seconds to complete. With larger plates, it may be necessary to add additional solvent (ether or grain alcohol) to the formula in order to facilitate pouring and delay the setting up of the collodion film prematurely. You’ll notice that solvents are continuously evaporating from the plate once the pour begins. Evidence for this evaporation is found in the obvious ethereal fumes and the rapid cooling of the plate in hand.
Prepare the salted collodion by adding iodide and bromide salts, grain alcohol and ethyl ether to plain collodion. (Note: flexible collodion will not work. You must obtain and use Collodion USP in these formulations.) Most salted collodion solutions need to ripen for several days before use.
For safety reasons, the substitution of 190 proof ethanol or denatured alcohol is sometimes recommended in these formulas in place of any additional ethyl ether. Since ethyl ether is extremely volatile, highly flammable, and potentially explosive, collodion formulas should be mixed and stored away from ignition sources (open flame, hot plates, electrical fans, etc.).
In general, working collodion solutions contain approximately 1.5% bromide salt and slightly more than double that amount of an iodide salt. Common anions of these salts include potassium, ammonium, cadmium, lithium, zinc, or sodium ions. Collodion formulas containing only potassium bromide and potassium iodide salts will clear quickly and be ready to use the same day, but their keeping properties are reduced. On the other hand, cadmium collodions may take several days to ripen, but will age more slowly. Ammonium salts also are used in quick-clearing formulas but they may produce irritating fumes and shorten the life of the working collodion as well.
Iodides add speed to collodion while bromide salts extend the spectral sensitivity and produce lower contrast results with a finer gradation in midtones. As any collodion ages and turns from light straw to red in color, the contrast generally increases and the speed of the emulsion decreases.
Addition of either potassium bromide or potassium iodide in the formula will also cause any bromidized collodion to throw down a precipitate which may take several days to clear.
This is a double-cadmium salt collodion that has a long storage life and a slightly greater spectral sensitivity than some other formulas. Because cadmium salts are used, the collodion tends to be more fragile and has a tendency to lift from the plate surface. Subbing the plate edge with cotton swab saturated with albumen helps adhere this collodion film to the plate. Note that cadmium salts are carcinogenic and should be handled using appropriate personal protection equipment.
Due to storage concerns and the difficulty obtaining diethyl ether, many wetplate photographers substitute either grain or denatured alcohols for any ether other than that inherent in the Collodion USP as purchased. Such low-ether mixtures may contain more water than usual due to its presence in the grain alcohol. The additional presence of water in the collodion may result in tender films, reduced adhesion to plates, and the need to extend the interval between pouring and sensitizing the plate. As a result, you may find in your practice that the traditional amount of ether is a necessity.
There is some anecdotal evidence that the substitution of denatured alcohols for either grain alcohol or ether may rejuvenate salted collodions or prolong the working life of the mix. However, be aware that denatured alcohols are manufactured to be intentionally toxic and any ingestion or prolonged exposure to the fumes of denatured alcohols is to be avoided.
Quick-clearing collodion formulas may be found in several texts devoted to wetplate. (Consult the bibliography.)
Quinn Jacobson's popular quick-clearing collodion formula is a modified version of a formula originally published in M.H. Ellis' 1856 book, "The Ambrotype & Photographic Instructor." The following recipe makes 570ml of working collodion. It can be used almost immediately.
A sensitizing bath consisting of 9% silver nitrate with pH adjusted to make either negative or positive plate. The actual volume of silver nitrate solution required depends upon the plate size being used and the capacity of the tank used for sensitizing the plates. More neutral baths (pH ~ 6) work well for negative images while positives require an acidic bath (pH ~4-5). Drops of nitric or glacial acetic acid may be used to adjust the pH. Inexpensive pH monitoring paper or dedicated pH meters may be used to determine solution pH.
Once prepared, the specific gravity of the bath should be measured with a hydrometer and the initial value recorded. A brewing or aquarium hydrometer is accurate enough for this measurement. As the bath is used and the silver removed during sensitization of plates, additional silver nitrate should be added to replenish the bath and bring it to its initial value.
The silver bath should be slightly iodized by letting a coated salted collodion plate sit in it overnight before the initial use of the bath.
Check the initial specific gravity of the solution using a hydrometer. Most inexpensive hydrometers used in brewing or aquarium applications will work. You don’t need to purchase an expensive laboratory hydrometer. Just be sure the hydrometer measurement range will incorporate values around 1.07 which is a fairly standard measurement for the sensitizing bath. Record the initial specific gravity level of the silver bath. (I mark the hydrometer scale directly). The bath may be replenished using a 30% silver nitrate solutions or by adding crystalline silver nitrate as needed.
Development should be timed to about 15 seconds and ended before shadow details become present. In hot conditions, the activity of the developer may be reduced and chemical fogging controlled by several means. These include dilution of the developer with additional water, reduction in the amount of ferrous sulfate, increasing the acetic acid content, or use of an organic restrainer such as sugar in the formula.
For negatives, a weaker developer is used for an extended time, generally about 90 seconds. Less ferrous sulfate and more acetic acid is used.
In case of any unevenness of flow of the developer over the plate, a greater addition of alcohol will help the solution flow better. (Some workers exploit this fact and use less developer to increase development streaks and other artifacts.)
Adding small amounts of potassium nitrate or silver nitrate will help brighten positive plates and produce a more neutral color. A few drops of silver from the sensitizing bath will also help produce a brighter plate. Many workers also save the used developer and mix it up to 50% with fresh developer to obtain similar results.
Filtering both fresh and used developers helps prevent small artifacts known as “comets” on the collodion plate. A cotton ball or two placed in the neck of a funnel makes a filter sufficient for this purpose. Silver nitrate solutions should also be filtered after daily use employing a dedicated funnel and fresh cotton to prevent contamination.
Plates are fixed for twice the time they take to clear or fully reverse in the case of positive images. Do not overfix plates. Areas of collodion along the pour-off corner may be thicker and impervious to the fixing action, but otherwise the unexposed opaque bluish collodion film should clear before the plate is removed from the bath.
Mix the contents together in a clean condiment squeeze bottle by shaking. The whiting will settle out so be sure to shake vigorously before use. Apply a small puddle to the center of the glass plate and thoroughly clean the surface by rubbing with a soft cloth or paper towel. (I prefer to use PEC Pads due to their durability when wet.) Be sure to polish the cleaned plate with a lintless cloth and remove any powdered whiting that may remain on the plate including the edges. Whiting is powdered calcium carbonate and the inadvertent introduction of this chemical into the silver sensitizing bath will raise the pH and cause problems.
In a lidded canning jar, dissolve the gum sandarac crystals in the alcohol by periodically shaking the bottle. It may take several days to completely dissolve the sandarac. Grinding the sandarac crystals to a smaller size using a mortar and pestle will speed the dissolution. Filter to remove debris. Add the oil of lavender to the filtered sandarac solution and mix until uniform. Decant the varnish into smaller stoppered bottles.
To use, slightly warm the varnish bottle in a water bath while gently heating the back of the plate over a paraffin lamp. Metal plates will warm rapidly while glass plates will take longer. Don’t try to rush with glass because a sudden temperature shock may crack the glass.
Remove the plate from the proximity of the lamp and then flow the varnish smoothly over the plate as if making a collodion pour. Let the plate rest horizontally for several seconds but not for too long since the alcohol in the varnish may begin to dissolve the collodion film. After several seconds, tip the plate vertically and from one corner, drain the excess back into a separate collection bottle. Filter the varnish again before reuse.
Warm the back of the varnished plate over the lamp in order to evaporate the alcohol solvent and set the varnish. Be careful to warm the plate slowly and avoid ignition of the alcohol coming off the surface. The varnish will take several hours to dry completely so keep the plate away from dust during this time.