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Ambrotype Process: Wet Collodion Positives on Glass Mark Osterman

[Published in Photographic Possibilities, 3rd edition, 2009 Robert Hirsch]

Invented in the mid-1850s the ambrotype is a direct positive variant of the collodion process on glass. An ambrotype can be made either by exposure in a camera or by projecting a positive transparency onto the sensitized plate using a conventional enlarger. The term ambrotype comes from the Greek root ambrotos, meaning "imperishable." At the time the process was first patented in 1854 by James Ambrose Cutting, it included a finishing procedure of hermetically sealing the surface of the image with Canada balsam and a second sheet of glass (a Cutting Ambrotype). The finishing technique fell from favor, but the name came to be used for all collodion direct positives on glass. Ambrotypes, and its close relative, the ferrotype/tintype, rely on the characteristic of the collodion process to produce image particles of very fine reflective metallic silver. These light colored particles establish the white parts of the image while the dark shadows are created by backing the clear glass plate with dark material or simply using dark glass. The ferrotype technique is identical to that of the ambrotype, the only difference being the black enamel metal plates used for that process. A collodion negative is made by increasing both the exposure and development along with slightly different formulas for the collodion and developer. The basic process of making an ambrotype is outlined in Box 10.1 Box 10.1 Making an Ambrotype 1. Preparation of the glass plate; cutting, cleaning and polishing. 2. Coating the plate with iodized collodion. 3. Sensitizing the collodionized plate in silver nitrate. 4. Exposure in the camera or under an enlarger. 5. Development with acidified ferrous sulfate developer. 6. Fixing the image in either cyanide or hypo. 7. Drying and varnishing the plate. Making Photographic Collodion

To make an ambrotype one needs to prepare the collodion, silver sensitizing solution, developer, fixer and varnish following the well-tested procedures worked out by photographer/historian Mark Osterman. Osterman's basic formula has a shelf life of one year if the stock is kept in a cool place. If cadmium bromide is difficult to purchase one may substitute potassium bromide. However, if potassium bromide is used, the collodion will have a shorter shelf life resulting in a faster shift of color from orange to deep red, an indicator of a gradual loss of sensitivity. The use of "Plain collodion" requires dilution with solvents and the addition of an iodide and bromide before it can be used as photographic (or salted) collodion. Materials Needed Plain collodion, USP (United States Pharmacopeia) Ethyl ether (anhydrous, reagent grade) 190 proof or 95% grain alcohol (ethanol); often purchased under the brand name "Everclear" Cadmium (or potassium) bromide Potassium iodide Distilled water 300 ml capacity clear glass bottle 100 ml beaker Glass, plastic or stainless stirring rod Small plastic syringe marked in milliliters Collodion Procedure 1. Pour 118 ml plain collodion into the bottle. 2. Add 77 ml ether and cap the bottle. 3. Add 2 ml heated distilled water into the 100 ml beaker with the syringe and add to this 1.5 grams cadmium (or potassium) bromide. Stir until completely dissolved. 4. Add to this same beaker 2 grams potassium iodide. Stir until dissolved and then add 77 ml of the alcohol. 5. Add the iodide/bromide alcohol solution to the collodion and agitate gently. After the initial agitation, the bottle should be kept upright and not shaken. The collodion may be cloudy when first mixed, but eventually clear leaving a transparent yellowish liquid with some solids settling on the bottom. This process can be encouraged by placing the bottle in a pan of warm tap water and burping the cap from time to time. Once clear, the collodion is ready to use. Sensitizing Solution: Silver Bath Materials Needed

Silver nitrate crystals Distilled water Glacial acetic acid or dilute nitric acid pH test strips (in the acidic 3-6 range) Dark brown glass storage bottle Latex gloves Eye protection The quantity of sensitizer needed is based on the size of plate you want to make and the means you choose to use it. Sensitizing can be done in a tray or a vertical tank. If the outside temperature is higher than 80°F (27°C) you may need to add more acid to prevent fogging of the plate, but this will reduce the plate's sensitivity. Sensitizing Procedure 1. Pour 1065 ml distilled water into the dark brown storage bottle. 2. Add 84 grams silver nitrate. Stir until dissolved. 3. Test pH and if the pH is higher than 5, add acid several drops at a time, until pH is less than 5. This formula is for a 1065 ml bath. To adjust for a different quantity, allow 28 grams of silver nitrate for every 355 ml. of distilled water. The Developer Materials Needed: Iron (ferrous) sulfate Glacial acetic acid Distilled water Alcohol Plastic funnel with wide spout Cotton wadding for filtering 500 ml beaker 50 ml storage bottle Mixing Developer 1. 2. 3. 4. 5. Pour 355 ml. distilled water into 500 ml beaker. Add 15 grams ferrous sulfate and stir vigorously. Add 14 ml glacial acetic acid. Optional: Add 18 ml of 190 proof alcohol Put loosely packed cotton in the neck of the funnel and filter the developer. Repeat this step at least two more times; cleaning the funnel,

beaker and bottle with clean water at every opportunity and packing the cotton tighter each time. Alcohol is added as needed to prevent the developer from beading up on the surface of the collodion plate. This will be required as the silver bath is well used. Hot temperatures make chemical reactions occur faster. If the outdoor temperature is higher than 80°F (27°C) you may need to add more water or acetic acid than normal to restrain the action of the developer to allow a more manageable development. The Fixing Solution Potassium cyanide or sodium thiosulfate (AKA hypo) may be used. Cyanide is preferred as it leaves a brighter deposit of image silver than the sodium thiosulfate, but it is extremely poisonous and must be handled with the up-most care. Both fixing agents are simply mixed with water and should be replaced at the end of each session of fixing plates. Quantities needed are based on the size of the tank or tray used for fixing. Stock cyanide fixer should be mixed in a sturdy plastic bottle. In either case, make only what is needed for a day's needs. Fixer Formulas Potassium cyanide Water - orSodium thiosulfate Water 15 grams 950 ml 140 grams 900 ml

Safety Alert: Potassium cyanide is extremely poisonous and extra caution must be taken when handling it. Precautions include: Keeping it away from all living creatures; wearing gloves when mixing or using either fixer; labeling all containers; and keeping it from contact with any acid, as the mixture of the two will produce deadly cyanide gas. The Protective Varnish Plates should be varnished to protect their fragile surface from abrasion and darkening due to exposure to sulfurous atmosphere. The following is a typical "spirit" varnish that can be applied. Varnish Formula Gum sandarac tears 190 proof grain alcohol Oil of lavender 57 grams 415 ml. 45 ml.

Place alcohol, gum sandarac, and oil of lavender into a wide moth mixing jar with a lid. Agitate the solution until the sandarac dissolves completely. This will take about an hour or two with continuous agitation. Alternatively, after the initial agitation the jar can be left undisturbed for a few days. Once the sandarac is dissolved completely, filter the varnish at least five times with progressively tighter cotton through a small funnel. The final varnish should be light yellow and completely clear and can be placed in a storage bottle. The Collodion Darkroom Collodion is a "colorblind" process that is not sensitive to certain shades of red, orange, yellow, brown, and warm green light. Your darkroom should be lighted using a deep orange or warm red filter. Deep red glass, available from a stained glass supplier can be fitted over an electric light or in a window for darkroom illumination. A Thomas sodium vapor safelight is perfect. The Camera Any view camera will work as long as you can get the plate safely into the film back without exposing it to white light. While learning the process, use smaller plates to reduce expense. Standard sheet film holders for 20th century view cameras can be modified to take glass plates. Additionally, images can be made from positive transparencies under the enlarger. Glass Preparation Cut glass to the desired size with a straightedge and glass cutter, available from a hardware store or have the glass professionally cut. Roughen the razor sharp edges on both sides with a sharpening stone. Cleaning the Glass Glass must be scrupulously clean before coating with collodion or the emulsion will peel during processing. Make a solution of glass cleaner by mixing equal parts water, alcohol and whiting, available from a stained glass supply. Rub a small amount of this solution on the glass and rub vigorously with a piece of cotton or clean, linen cloth until most of the solution is absorbed into the cloth. Pay special attention to the edges. Repeat this same operation on the other side. Polishing the Glass Using a clean piece of cloth wipe the outer edges free of any powder and polish both sides of the plate. Test the polish by breathing on the surface and observing the condensation. If there are any streaks or markings, the plate requires more polishing.

Coating the Plate Under white light (daylight), hold the plate in the left hand by the lower left corner. Pour a large puddle of the prepared photographic collodion onto the center of the plate and then gently tilt the plate so the collodion goes to the lower left corner, the upper left corner, the upper right corner and finally the lower right corner. Drain the excess off the lower right corner back into the bottle. While the collodion is draining, rock the plate from side to side to prevent lines from forming in the direction of the draining solution. Keep the drained corner of the plate slightly lower than the rest to prevent it from flowing back onto the plate. After the surface of collodion shows no more fluid movement (about five seconds) put the plate, collodion side up, immediately into the prepared silver nitrate solution (see illustration 10.?). If the collodion begins to dry before it's put into the silver, the sensitizing will not be effective. Safety Alert: Wear gloves after the collodion is poured and until the plate is washed thoroughly after fixing. Sensitizing the Plate Sensitizing can be done in a tray or vertical tank under safe light conditions. Bring the plate into the darkroom (or turn off the white lights) and place the plate into the silver solution. If you are using a tray, slide the plate collodion side up quickly under the surface. Any hesitation will leave a mark in the final image. If you are using a vertical tank, place the plate on the dipper and slide it into the silver solution in one easy motion. The plate is ready to remove when the silver solution drains from surface of the collodion without lines or beads. Remove the plate by a gloved hand when using a try or with the dipper when using a tank. Allow the excess to drain and rest the edge of the plate on a piece of paper towel to draw of more of the excess silver. Exposing the Plate Place the sensitized plate in a light-tight film holder and expose with a view camera or under an enlarger. Exposure is determined by trial and error, judging over or underexposure of the developed plate by observing the degree of shadow detail. Collodion plates are about ISO 1 and become even less sensitive as the collodion ages. Light meters are not helpful due to insensitively to red wavelengths of light. Plate Development: Tray & In-Hand Methods

Under safelight conditions, a plate can be developed two ways, in a tray or in the hand. The tray method is easier, but the images are usually not as strong as those developed in hand. Tray Method Pour a little more developer than will be needed to over the plate. Tilt the tray so all the developer is on one end and place the plate, collodion side up, on the upper end of the tray. In one quick motion, rock the try to make the developer flow over the entire plate and continue rocking for a few more seconds. In-Hand Method Hold the plate in one hand with a slight incline to allow the developer to flow easily across the surface. Gently pour just enough developer to cover the plate along the edge so that it slowly flows across the surface; the less developer, the stronger the image. Do not splash the developer onto the surface as this produces a weak, thin image. Rock the plate to distribute the developer and try to keep the solution on the surface without draining off the edges. Development should be stopped before you see any of the deepest shadows of the image. If the image is fully formed before 10 seconds, it was probably overexposed. If it took longer than 20 seconds, it was likely underexposed. Development is stopped completely by gently flowing clean water over the surface and back of the plate. Tap water is fine as long as it does not contain iron particles, which may leave specks all over the image. This washing step should be done as long as it takes to observe the water flowing off the surface without streaks or beading. Fixing and Washing the Plate Fixing can be done in a tray or in a vertical tank under daylight conditions. Place the plate image side up into the fixing solution. This will remove the light colored silver iodide. If you choose to use sodium thiosulfate it will require a fixing time of four more minutes than it takes to clear the image and washing time of at least five minutes, though more is probably best. Cyanide fixing on the other hand is based on observation. Fix until you see all the silver iodide removed and then leave the plate in the fixer for about two times more than it took to make the visual change. Cyanide will begin to dissolve the image bearing silver if this step is prolonged, though this effect may actually be used to increase the shadows of the image. While the washing step for cyanide fixed images can be shorter, as with the sodium thiosulfate, it is always better to wash as long as you can to remove residual chemicals. Drying and Varnishing the Plate The washed plate may remain in a tray of clean wash water can be kept for over a year. When it is convenient to complete the process, rinse the collodion side of the plate with distilled water and either place it on a drying rack or gently heat it

from below with an alcohol lamp. Keep the plate moving while drying with the lamp to prevent unequal heat, which can cause the plate to break. Keep the plate from getting too hot. When the water has evaporated from the surface, alcohol and ether in the collodion will begin to evaporate leaving the image a lighter color than when it was wet. Historic examples were often left in this state and carefully sealed in presentation cases. Unvarnished images will tarnish to a dark grey blue if not properly sealed from the sulfurous atmosphere, therefore varnishing collodion plates is recommended using the method that follows. Heat the prepared varnish by placing the pouring bottle in a cup of warm water. An inexpensive electric coffee cup warmer is ideal. Heat the plate to around the same temperature as the varnish. If the plate is too cold or too hot, the varnish will not flow evenly. Pour the varnish the same way you poured the collodion keeping the final draining corner lowermost until the varnish has set. You may wick off some of the excess varnish by turning the plate vertically and resting the lower edge of the plate on a paper towel. Once set, the plate should be held over an alcohol lamp and warmed to drive off the excess the alcohol solvent. Once again, keep the plate moving and do not let the plate get to close to the flame or the varnish may catch fire. Housing the Plate Allow the varnish to out-gas as long as you can before framing; the longer the better. In the 19th century they cased them immediately after varnishing, but we let them out-gas on a rack for at least three days before putting them in a envelop. Do not try to remove dust, hairs, lint or any other matter for several days and when you do, use compressed air. Never touch the surface of the plate or you will leave a mark. Ambrotypes on clear glass will require a dark backing to make them appear as positives. Paint, black varnish, dark cloth or paper were all used during the collodion era. However, do not apply paint or black varnish to the collodion/varnished side of the plate. Over time, this may peel, taking the image with it. You may also apply blacking selectively to certain areas and then place one image upon a second in a variant called the relievo ambrotype. The image should be framed under glass and with a mat to prevent the collodion image from touching the cover glass. If the varnish was applied correctly, the image will live up to its Greek root as immortal. Ambrotypes from the 1850s, made according to the process described, are often found in an excellent state of preservation. Supporting images included ambrotypes and the conversion film holder designed by Osterman

Copyright 2009, Mark Osterman, Process Historian Advanced Residency Program in Photograph Conservation George Eastman House, International Museum of Photography, Rochester, NY


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