The Wet-Plate Process
Both methods of wet plate use silver-halide crystals in a collodion emulsion that reacts to the light of the scene. The process is similar to standard film, only the plate must be exposed and developed while still wet with chemicals. It’s then fixed immediately to prevent overdevelopment, scratching, tarnishing and fading. There are numerous workshops from practicing photographers like John A. Coffer, Kerik Kouklis, William Dunniway, and Mark Osterman and France Scully Osterman, who also wrote an in-depth manual called Basic Collodion Technique: Ambrotype & Tintype Quinn Jacobson offers a book with accompanying video tutorials called Positive Wet Plate Collodion, and in New York, the Penumbra Foundation offers several classes on alternative photographic processes like wet plate.
As many of these chemicals are flammable and poisonous, like cyanide or silver nitrate, which can blind you if it gets in your eyes, it’s advisable to be cautious and follow proper safety practices. For instance, the first step is deburring the glass by polishing edges to avoid cuts and therefore any hazardous chemicals that could be introduced to your system. The face of the glass also needs to be polished with solvent because any imperfections or leftover residue could ruin the exposure or keep the emulsion from holding to the plate. The collodion is a sticky solution made from pyroxylin, ether and alcohol. Bromide and iodide salts are added and dissolved in the collodion. Historically, it’s aged for approximately one week, but there are ready-to-go, premixed collodion and wet-plate kits available online, as are developers and varnish.
The collodion mix is poured and spread evenly over the plate, rotating corner by corner, to saturate the glass equally in all areas without lines or spots, with excess draining back into the bottle. Let the collodion set for 20 to 30 seconds; then, in the darkroom, the saturated plate is dipped into a silver-nitrate bath for three to five minutes where the silver nitrate will bind with the iodide and bromide salts to form a light-sensitive silver-halide coating. (You can use an enclosed sensitizing tank or vertical bath to work in daylight.) This is an opportune time to compose your subject and shot prior to adding the wet-plate backing because it will block your view of the scene and the solution is drying rapidly at this point. The drier the plate, the less responsive it will be to light. Silver nitrate will drip from the plate, as well, so be prepared for any mess.
Excess silver nitrate is drained from the plate back into the mixture and then the plate is added to a wet-plate holder facedown and loaded onto the back of the camera. After affixing the wet-plate back to the camera, a "dark slide" in the
wet-plate housing slides up to reveal the plate to the interior of the camera. Then the lens cap is removed to make the exposure, which can last from a few seconds to several minutes, depending on the collodion mixture, lens and aperture, and the amount of light in the scene. (These are very old cameras and lenses, so obviously there are no automatic functions; exposure and timing will take practice to perfect.) The exposure is halted by replacing the lens cap, and the dark slide is slid back into place before removing the wet plate to the darkroom, where it will be developed.
Developer, in this case a solution made from iron sulfate, distilled water, alcohol and acetic acid, must be spread evenly and carefully over the surface to reduce uneven exposures and any aberrance like wet spots or creases in the grain. (These effects can be desirable if looking to simulate the aesthetic of an older print.) Developing is very fast; images will start to appear within seconds, and the exposure should fully fade in at around 20 seconds. If it appears too quickly or slowly, you most likely have over- or underexposed the image, respectively. Once shadows begin to fill in (they should not), a water rinse will halt the development, and the plate must be agitated gently in a chemical solution of sodium- or ammonium-thiosulfate (or potassium cyanide in another method for richer tones) to remove excess light-sensitive silver-halide crystals, which could alter the exposure over time. The rule of thumb is to double the previous development time in the fixer. So, if your developer took roughly 20 seconds, a 40-second bath in fixer should do.
After the fixer, the wet plate is washed in water once more for around 15 minutes before it’s dried on the rack. It also can be dried gently over open flame to heat the plate for the next step, which is varnish. While still warm, the plate must be varnished evenly on the emulsion side with sandarac varnish, a mixture of sandarac resin, alcohol and oil of lavender. Follow the same coating process as you did with the collodion, from corner to corner, with excess varnish removed and drained back into the bottle. The plate is heated once more over flame to set the varnish. When using transparent glass, the final step is to black the back with a layer of glossy or matte black paint to enhance the image against a black backdrop. It’s suggested that this step is performed twice, with the plate drying overnight between each time.