Making, Coating and Processing a Mid-1880 Era Gelatin Emulsion

Copyright 2007 Mark Osterman, Process Historian
George Eastman House, International Museum of Photography, Rochester, NY

By the1860s, curious amateurs had invented three major variants of the wet-plate collodion process; preserved (moist) collodion, dry collodion and collodion emulsion. Unlike the former two, collodion emulsion relied on actually adding silver nitrate to the halides in the collodion binder before it was applied to the plate. The basic concept that evolved from making collodion-based emulsions was the beginning of emulsion photographic technology for the next 150 years.

Like the daguerreotype and collodion processes that preceded them, all gelatin emulsions begin as mostly sensitive only to blue, violet and ultra violet light. However, depending on the procedure, early gelatin emulsion plates could be ten to fifteen times more sensitive than the typical collodion negative.

Making gelatin emulsions in the mid-1880s was not particularly difficult, once the basic concepts were understood. Hand coating these early plates was also very easy when compared to coating panchromatic emulsions in total darkness. Today, an individual can, without expensive equipment, make a similar emulsion that is perfectly suited for hand coating plates for negatives, positive transparencies, opaltypes, orotones and gelatin tintypes.

The purest gelatin used in the earliest days of dry plates was probably not so different than good quality food grade gelatin available today. It was processed from the hides of cattle. As the speed and spectral sensitivity of emulsions was increased, the purity of this bovine gelatin became more of an issue and photographic grade gelatin was introduced. Photographic grade gelatin was, and still is, much more pure than the food grade variant. It is probably not a coincidence that the Genesee Pure Food Company (later to be known as the Jell-O Company) was established in Le Roy, NY only a few miles from Rochester and the Eastman Kodak Company, the leading buyer of raw unprocessed gelatin.


Basic Theories of Emulsion Making

It’s difficult to know just how much information to include in a basic set of instructions but the following will give the beginner a good start. Though it’s really a suspension, the end product of this technique has become known as an emulsion. The goal is to produce a liquid that suspends the silver halide particles and keeps them from precipitating to the bottom of the beaker. Before actually making a silver bromide emulsion, it’s very instructive to do the following experiment with silver nitrate and common salt to understand the mechanics of the process.
 

Equipment and Materials

1. safety goggles
2. latex gloves
3. two 200 ml Pyrex beakers
4. plastic, stainless or glass stirring rod
5. heat source (alcohol lamp, hot plate )
6. eye dropper
7. 2 grams silver nitrate crystals
8. 4 grams sodium chloride (common table salt)
9. 5 grams gelatin (any grade)

Part A.

In a clear glass 200 ml beaker dissolve 2 grams sodium chloride (table salt) in 100 mls distilled water. In a second beaker, dissolve 1 gram silver nitrate in 50 mls distilled water. Using an eye dropper, put all of the silver solution, drop by drop into the chloride solution while stirring with a glass rod. The silver will bond with the chloride creating white silver chloride. This will eventually fall out of solution to the bottom of the beaker. [Both Thomas Wedgwood and Nicephore Niepce applied this silver chloride paste to paper and exposed it to light to create printed-out photolytic silver images.]

Part B.

Place 5 grams photographic grade gelatin in a 200 ml beaker with 100 mls distilled water. Allow the gelatin to swell for 15 minutes. When swollen, heat this solution until the gelatin melts completely. Add to this 2 grams sodium chloride and stir until dissolved. In a second beaker, dissolve 1 gram silver nitrate in 50 mls distilled water. Using an eye dropper, put all of the silver solution, drop by drop into the chloride solution while stirring with a glass rod. This time the silver chloride will stay suspended in the gelatin mixture creating a milky white silver chloride gelatin emulsion.


Types of Gelatin

With the steady decline in silver based photography at the time of this writing, it is assumed that photographic gelatin will become increasingly more difficult to find. There were three basic forms of processed bovine gelatin in the late 19th century; glue, food grade and photographic grade. Glue is not suitable for photographic emulsions. It is possible to use food grade gelatin provided that it is of reasonable purity. Poor quality food grade gelatins may contain compounds that increase sensitivity of the emulsion causing non-image fogging. When using food grade gelatin, you will probably need to add more than the formula requires to achieve the same jelling characteristics as the photographic grade. This is not a problem as additional gelatin can be added at any time as required to set into a firm jelly at room temperature.

Gelatins are occasionally assigned a bloom rating, important to the setting potential. In the nineteenth century, gelatins were offered as simply hard or soft. If you are able to purchase gelatin with a known bloom rating use the higher bloom (hard gelatin) for the reserve gelatin added after digestion.


Relationship of Silver to Halides

The emulsion described herein is a silver bromo-iodide variety. The bromides are in excess to the iodides, and the total halides are in excess to the silver. This excess of bromide is important during the combining of the silver as it prevents potential fogging in the finished emulsion. When looking at the formula featured here, however, it appears that the weight of silver nitrate is actually larger than the total weight of the halides. This is because to accurately compare the ratio of silver to halides (bromide combined with iodide) one must convert the gram weights of the silver and halides to the molecular weight of those compounds being used.* This depth of understanding is only necessary if you are formulating your own emulsion formula or substituting one halide for another.

*[A metaphor might be that the sweetening power of a popular sugar substitute might be stronger than plain sugar, so equal amounts of these will have a very different effect. Therefore, it will take less weight of the substitute to have the same effect as sugar because of its greater sweetness.]


Effect of Adding Silver Nitrate to the Gelatin Halide Solution

The speed in which you combine the silver solution with the gelatin halide solution has much to do with the speed, density potential and resolution potential of the final emulsion. You have four ways to control this variable; the percent of gelatin in the gelatin halide solution, speed of agitation when combining the silver with the halide, the opening of the orifice on your syringe and how quickly the silver streams from the orifice. The slower the silver is introduced, the larger the silver halide grain size and the more sensitive the emulsion. When making your first emulsions, sensitivity is less important than making a clean, fog free plate, with a good range of tones. A very slow, fine grained emulsion is made by literally pouring the silver solution from a beaker, into the gelatin halide solution in a continuous stream while stirring.


Ripening and Digestion; Its Effect on Gelatin Emulsions

Once the silver solution has been added to the gelatin halide solution, the sensitivity of a simple bromo-iodide emulsion is increased by a process called Ostwald ripening. The hot emulsion is kept at a constant temperature that promotes the growth of larger silver particles that are, in turn, more sensitive to light than smaller particles. The hotter the temperature of the emulsion and the longer the ripening period, the larger the silver halide crystal will become. After ripening, the emulsion is chilled, washed and subjected to another treatment called digestion. This is another opportunity for the silver halides to grow by heating the emulsion for a given period of time.

Eventually heat digestion was replaced by chemical sensitization with ammonia, sulfides or other additives. It is digestion, however, that continues to increase the sensitivity every time a gelatin emulsion is reheated. If an emulsion is reheated too many times, or at too high a temperature, it will eventually become so sensitive that non-image fogging is the result. Reheating the emulsion also causes the gelatin to lose its setting characteristics which are absolutely crucial for successful coating and subsequent processing.


Washed Emulsion

When silver nitrate is mixed with a bromide and iodide, silver nitrate bonds with the halides creating light-sensitive silver bromo-iodide. In a process called double decomposition, a by-product of water soluble nitrates is also formed. When making developing-out emulsions with potassium bromide, the resulting soluble potassium nitrate must be washed away. The first step in washing the emulsion is noodling.


Noodling

The potassium nitrate is washed out of the emulsion by first allowing the hot emulsion to chill in a refrigerator to a stiff jelly. Once chilled, the emulsion is cut into shreds with a silver fork or squeezed through the small openings of a die or mesh to produce emulsion noodles. These noodles give the emulsion a greater surface area which aids in releasing the water soluble potassium nitrate when they are washed in cold tap water. After washing the noodles they are drained of excess water and re-melted leaving behind only light sensitive silver bromo-iodide in a gelatin binder.

Noodle washing was eventually replaced by dialysis and later, the application of special washing gelatins that precipitated the emulsion so that the potassium nitrate could be siphoned off the top of the emulsion. For the amateur emulsion maker, old fashioned noodle washing is still the easiest approach.

The following instructions are based on a mid-1880s formula and approach for making around 350 mls of a slow, clean working, blue-sensitive emulsion. You can make this emulsion more sensitive by adding the silver solution slower and/or ripening and digesting the emulsion longer; but as mentioned already, it’s better for the novice to start with slow emulsions.


Equipment and Materials Needed:

Equipment

Much of this equipment can be used for other historic photographic processes. The hot plate/stirrer, for example, is one of those pieces of equipment that is a great help for mixing all sorts of things. Pyrex glass beakers in assorted sizes are essential in every historic process darkroom. The crock pot and potato ricer are however specific to gelatin emulsion making, an activity very similar to cooking.

  1. safety goggles
  2. latex gloves
  3. Pyrex “tempered glass” laboratory beakers; one 500 ml & two 300 ml size.
  4. 1 ½ quart Pyrex “tempered glass” loaf baking dish for chilling
  5. heat source*
  6. thermometer (digital thermometers are cheap and perfect for emulsion making particularly when they have a built-in alarm)
  7. 3 quart glazed ceramic or stainless steel mixing bowl
  8. stainless steel wire mesh drainer big enough to rest in the opening of the aforesaid mixing bowl
  9. small brown ceramic cheese crock with wire locking ceramic lid
  10. 1 square foot of black plastic sheeting (must be opaque)
  11. 1 gallon bag made of black plastic sheeting (must be opaque)
  12. large plastic syringe (60ml/cc)**
  13. heavy duty stainless steel potato ricer
  14. refrigerator (a small dormitory type is perfect or use your household refrigerator) and ice cube tray
  15. electric crock pot
  16. 25” square piece of sheer white nylon or polyester cloth (for filtering)
  17. stainless steel spoon
  18. glass stirring rods
  19. red or deep amber safe light

* You can use a sauce pan on a hot plate or the crock pot (also listed) but a laboratory hot plate w/magnetic stirrer is perfect for emulsion making and well worth the expense. You can purchase them second hand on line.
** The Terumo brand 60 cc Syringe with Catheter Tip is perfect except that the opening of the tip is too wide. Go to the hardware store and buy a tube of glue that comes with a separate tapered tip of the same size. Make a pin hole in the end of the tip with a hot needle and push this firmly over the catheter tip of the syringe.

Materials

The quantities listed below are for making one batch of approximately 350 ml emulsion. Naturally it is a better plan to buy larger amounts any time you buy these materials as they are generally less expensive when purchased in quantity.
  1. 1 liter distilled water
  2. 10.5 grams potassium bromide
  3. 0.4 grams potassium iodide
  4. 12 grams silver nitrate crystals
  5. 21 grams gelatin (photographic grade is best, but you can use food grade)
  6. 5 grams chrome alum
  7. 1 grain thymol
  8. 5 ml 95% grain alcohol


Making the Emulsion

Take the time to read and visualize all of the following steps before you attempt to make the emulsion. You may want to practice step 5 with plain water to feel comfortable with the technique. Preparing all the materials and equipment prior to working under safelight conditions will make the procedure much easier to perform.

1. Put 3 grams photographic grade gelatin into a 500 ml Pyrex glass beaker with 85 mls distilled water. Allow at least fifteen minutes for the gelatin to become fully swollen and easily flattened (or squished) between the fingers. This is called the “first melt” gelatin.

2. Put 18 grams photographic grade gelatin into a 300 ml beaker and pour enough distilled water to cover the gelatin. Allow this gelatin to absorb as much water as possible. Different sources of gelatin absorb more water than others. You may need to add more water at a later time. This is called the “reserve” gelatin which will be drained and added to the emulsion after the first melt.

3. Dissolve the swollen first melt gelatin by placing the beaker in a hot water bath such as a small sauce pan with water on a hot plate or in a crock pot with just enough water to the level of the gelatin solution. You may also use a hot plate stirrer as long as the solution is kept in motion with the magnetic stirrer. Using a thermometer, try to keep the temperature around 120 degrees F.

4. Put 10.5 grams potassium bromide and .4 grams potassium iodide in the first melt gelatin and stir the solution until the halides are fully dissolved.

[Every operation after this should be done under red safe light. The darker the safe light and the less time you have the emulsion exposed to it, the better]!

5. Prepare the silver solution by dissolving 12 grams silver nitrate in a 300 ml Pyrex glass beaker with 85 mls distilled water. Heat this silver solution to around 120 degrees F (50 C) and draw some of this solution into the syringe. Slowly squirt the heated silver solution in a continuous stream with the tip below the surface of the gelatin halide solution while you stir it continuously (this is where a hot plate stirrer comes in handy). Refill the syringe and continue until all the silver solution has been added to the gelatin-halide solution.

[When making more sensitive emulsions you can be more accurate if you use a musician’s metronome to keep you on track as you gently and continuously push the plunger of the syringe. Try to make the plunger pass a ml marking on every click, or every other click, of the metronome.]

6. As you combine the silver with the gelatin-halide solution you will see the two clear liquids change into a milky white silver bromo-iodide emulsion.

7. After all the silver has been added, ripen the emulsion by maintaining the temperature at around 120 degrees F for 15 minutes with constant gentle stirring.

8. While the emulsion is ripening, begin draining all the excess water from the reserve gelatin. When digestion is complete, add the reserve gelatin to the emulsion and stir until the new gelatin is completely dissolved. When you first add the reserve gelatin the temperature of the emulsion will fall. Bring up the temperature of the emulsion back to 120 degrees F. and dissolve the reserve as quickly as possible. Make a notation of the time it takes for future reference.

9. Pour the hot emulsion into the glass Pyrex loaf pan and carefully slide this into the black plastic bag. Secure the opening of the bag so that no light can fog the emulsion. Place the bagged emulsion in the refrigerator for several hours or until completely set to a stiff jelly. The reason a shallow dish is used for setting the emulsion is so that it will chill faster and more evenly than if left in the beaker.


[In the following steps it is advisable to wear latex gloves; not because of potential silver stains to the hands, but to prevent contamination of the emulsion from your hands.]

10. Under red safe light remove the emulsion from the refrigerator and pull the dish from the bag. The emulsion will look white under the safe light (it is actually bright yellow). Scoop out the firm jelled emulsion with the stainless steel spoon and put it into the potato ricer.

11. Place the sheer white nylon fabric in the stainless steel wire mesh drainer in the mixing bowl and squeeze the ricer to create emulsion noodles that will fall into the center of the fabric. When the emulsion is completely noodled into the fabric, gather the edges of the cloth and secure them with a rubber band. Fill the bowl with cold tap water (add a few ice cubes) and move the noodle filled fabric around for about five minutes then let soak for five more without agitation. Change the water two more times and wash the noodles as before.

12. Drain the washed emulsion noodles thoroughly for at least 15 minutes and then place them into a clean Pyrex beaker.* Re-melt the beaker of emulsion in the electric crock pot at around 120 degrees F and add “finals.” The finals listed below are: chrome alum, added to make the emulsion set to a stronger film to withstand processing, alcohol to aid in coating and thymol, to prevent bacteria growth.

[No chrome alum in the emulsion may result in a very fragile film that can melt off the plate if processed in chemicals or washed in water that is too warm. Too much chrome alum will prevent the film from absorbing the chemicals effectively. Because the characteristics of each sample of gelatin are going to be different, the quantity of chrome alum may need to be decreased or increased as needed.]

* An old stainless steel developing tank is great for re-melting emulsions. The light trap in the lid allows you to keep the white lights on in the darkroom


Finals

   4 ml of a 5% solution chrome alum (5 grams chrome alum into 100 ml distilled water) Add the chrome alum drop by drop
   5 ml 95% grain alcohol
   1 grain thymol

When the finals are added and fully incorporated into the emulsion pour the entire contents into a brown ceramic cheese crock, cover the opening with a piece of black opaque plastic and secure the ceramic lid with the wire spring. Place the emulsion filled crock in the refrigerator for future use. Remove only what’s needed when coating a batch of plates by scooping out the chilled emulsion with a stainless steel spoon. The stock emulsion will last many months if kept cool and protected from white light.

These plates are blue, violet and ultra violet sensitive and fairly slow by modern standards. Assume an ISO rating of between 5-10 as a starting point. They are developed under red safe light, by inspection, which is a great advantage.


The Technique of Coating Glass Plates with Gelatin Emulsions
Coating glass plates with gelatin emulsions is a little different than working with a solvent based binder such as collodion, which relies on evaporation for the coating to set to a firm film. Gelatin emulsions must be heated to a liquid form, and once applied to the glass support, be able to set back into a firm jelly at an average room temperature. This so called “set time” or “setting time,” is governed by the ambient temperature of the room, the bloom and percent of gelatin and the quantity of alum added as a “final” to the emulsion.

Shortening the setting time was almost always done by quickly lowering the temperature of the emulsion. The most common approach was to level a piece of marble or thick glass and place the coated plates upon the surface until the emulsion cooled and became firm. The setting of emulsions on paper supports was generally accomplished by chilled air.

The earliest commercially made gelatin dry plates were coated by pouring the emulsion by hand. An 1884 account of the operation at the Cramer Dry Plate Works in St. Louis was described as “eight busy men, with pitchers of emulsion on one side, a pile of glass on the other and in front of them, a peculiar leveling stand.” *

* Philadelphia Photographer, Jan 1884, p 11

The following instructions are based on the techniques of the early 1880s, before the invention of cascade or transfer coating and continuous belt chilling chambers. This system is not difficult to master and enables one person to make dozens of plates in one sitting. The only limitation is the capacity of the drying box.


Equipment and Materials Needed

Equipment
  1. Glass cutter
  2. Cork backed straightedge
  3. Small sharpening (whet) stone
  4. 2” wide natural bristle paint brush
  5. Soft natural hair make up brush
  6. 2 wood plate racks (see Appendix )
  7. liquid dish detergent
  8. rottenstone or calcium carbonate powder
  9. ½ yard fine cotton or linen cloth cut into 5” and 8” squares
  10. Small stainless steel container with lid (an old stainless steel film developing tank is perfect)
  11. Electric crock pot
  12. Small ceramic tea pot, antique invalid cup or glass gravy separator
  13. Electric laboratory hot plate
  14. Paper towels
  15. 2 1’x1’ marble tiles or ¼ glass plates
  16. Small spirit level
  17. 2 wood leveling stands (see Appendix)
  18. Drying box (see Appendix)


Cutting & Cleaning Glass Plates

Window glass is good enough for hand coated photographic plates. Make sure you purchase these from a framing supply house in unopened boxes. The plates should be interleaved with paper to prevent surface scratches. If you have never cut glass before, pay a visit to a stained glass shop, purchase the best glass cutter you can afford and ask for a demonstration.

Cut the glass to the desired size and never lay the plate surface down on anything or it will become scratched. Place the plate upright against a wall or in a wood rack. It is extremely important to remove the razor sharp burr on all the edges on both sides with a small hand sharpening stone. Dust off the powdered glass dust with a stiff natural brush. This is also a good time to check if the plates fit your holders before you coat them.

Apply a drop of detergent to each side of the glass and wash the plate under warm running water rubbing the surface thoroughly with a small square of cotton cloth. If the plates are particularly dirty you may add a dusting of fine rottenstone or calcium carbonate to each side with the detergent. Keep washing in running warm water without the cloth until the water sheets off evenly. Handling by the edges only, place the plate upright in a rack on a piece of blotting paper to dry. Once dry, breath on the surface of the plate and rub the condensation with a clean piece of the larger cotton cloth squares until you see no streaks. I have never needed to sub plates for gelatin emulsions as long as they were washed thoroughly.


Heating and Pouring the Emulsion (under red safe light)

The whole coating procedure requires very little time; less than ten seconds for a 5x7 plate from the initial pour to placing the plate on the chilling table. It is similar to coating collodion plates, though not exactly. Naturally all of the following is performed under deep red safe light conditions. Before you turn off the white lights, level your chilling tables using the spirit level.

1. Remove the emulsion from the refrigerator. Scoop out enough cold gelatin emulsion for several plates and place this in a stainless steel container (developing tank) with a lid. Put the tank containing the emulsion in a heated crock pot and with enough water to keep the emulsion warm without having the container float or flip over. Heat the emulsion until it is very liquid. The actual temperature will depend on the pouring qualities of each batch of emulsion.

2. When the emulsion is thoroughly liquefied, pour some through a large square piece of clean cotton fabric into the pouring cup (I prefer the antique invalid cup). Allow the emulsion to settle so that the bubbles rise to the top and pop. The pouring cup can be kept warm in the crock pot between pouring plates.

3. Slightly heat the plate of glass by placing it on the surface of a warm (not hot) laboratory hot plate covered with two layers of paper towels. While the plate is still warm hold it in the left hand with the fingertips supporting the back of the plate. Give the plate a quick dusting with the make-up brush.

4. Holding the pouring cup in the right hand, pour a sufficient quantity onto the center on the plate (pouring too little is worse than pouring too much). Keep the plate level so that the creamy emulsion forms a perfect circle. If the emulsion is oblong shaped, the plate is not level.

5. Gently tilt the plate so that the emulsion flows to all four corners without going over to the back side. Once the plate is completely covered, gently let some of the emulsion flow off one corner of the plate back into the pouring cup and immediately afterwards pour some of the excess off from the opposite corner into the pouring cup. Each corner from which you poured the excess will drip a small amount of emulsion that rolls to the back of the plate. Do not worry about this, it is typical of hand coated gelatin plates and this artifact can be seen on historic examples.

6. Gently roll the plate for a couple of seconds so that the emulsion redistributes evenly on the surface and immediately place the plate on the leveled chilling slab. The emulsion should still be warm and still fluid enough to level itself on the surface of the plate before it begins to set to a firm even coating.

7. As the gelatin begins to set up you will probably see some dimples on the surface and possibly some dust. Move the plate to the next chilling table until the emulsion is firm enough to place upright on a rack in the drying box. You can test the firmness of the emulsion by touching on corner with your finger, though with experience you’ll eventually have a sense when they’re ready to be removed from the slab.

The slower gelatin emulsion plates are dried the better. Fast drying can cause ridges in the surface of the emulsion. Make sure the drying box is absolutely light tight but fitted with adequate ventilation. Collect the dry coated plates the next day and place them in a light proof box interleaved with clean paper until needed.


Processing Gelatin Emulsion Plates

The earliest developers used for gelatin emulsion plates were based on either ferrous oxalate or pyrogallic acid, known simply as pyro. Unlike the calotype, albumen negative or collodion processes, all of the developing agents for processing gelatin emulsions were used in an alkaline state. Ferrous oxalate was one of the first developers used for gelatin plates, though it fell from favor by the end of the century. Pyro was introduced in the 1850s to develop collodion negatives and has continued to attract devotees well into the 21st century for development of silver based film stock. Pyro development produces warm brown silver deposits with a slight yellow stain.

By the 1890s, hydroquinone and metol based developers were being offered by photographic suppliers. Metol developers produced cool, blue-black silver deposits and developed very quickly though with little density. Hydroquinone development resulted in warm black silver deposits that developed slowly with greater density potential than metol. By the late 19th century, most photographers chose either pyrogallic acid or a combination of metol and hydroquinone, simply called “MQ.”

A typical developer formula for processing gelatin emulsions has the following elements; the reduction agent (pyro or metol/hydroquinone), an alkaline accelerator (ammonia or sodium carbonate), a restrainer (usually potassium bromide) and a preservative such as sodium sulfite. By knowing the function of these components, a photographer could tweak the formula to suit specific needs and correct exposure problems to some degree.

Development of emulsion plates is most easily done in either a white enameled or glazed ceramic tray so that the progress of development can be easily viewed by safe light. All other chemical operations can be done in any type of tray, though Pyrex glass is always the best choice as it is easily cleaned. Development is done under either a red or deep amber safe light. The effect of over or under exposure can be seen during development and the knowledgeable photographer has the opportunity to adjust the developer as needed to produce the best possible results. It was typical in the 19th century for the photographer to have small bottles of accelerator and restrainer liquids at the ready near the processing sink.

On occasion, photographers had problems with the emulsion lifting from the edges of the plate; an effect called “frilling.” Assuming the glass support was properly cleaned, this usually happened when the developer was either too alkaline or the temperature of the developer was too hot. A simple 2% alum hardening bath before or after development, or a little alum added to the fixing solution was usually enough to prevent frilling.


The Basic Procedure [under red or deep amber safe light]

The exposed plate is placed, emulsion side up, into the white tray containing enough developer to cover the plate. The developer should be used at a temperature of around 65 F. It is necessary to rock the tray during the development so that fresh developer is always in contact with the emulsion.

When developing by inspection, the most common mistake is to stop development too soon. The maximum density of an image always looks much darker when the plate is in a white tray. It will be necessary to lift the plate from the tray and inspect the progress by looking through the plate, illuminated from behind by the safe light. An average, properly exposed landscape negative develops gradually with the sky visible first, followed by architecture and eventually well lighted foliage. Do not expect to see details in the deep shadows of foliage due the insensitivity of a blue sensitive emulsion.

Once development is judged to be complete, the plate is washed under gentle running water for two minutes or in a tray with two changes of water and gentle agitation. Do not use an acid stop bath as this may shrink the emulsion causing frilling. Fix the negative in a tray of sodium thiosulfate for five minutes with occasional agitation. Wash the plate in several changes of fresh water or running water for at least 20 minutes and then place on a rack in a dust free place to dry.


Formulae

Kodak Dektol can be been used effectively for processing the emulsion described earlier in this section. Begin by using it undiluted and dilute with water if you feel the maximum highlight density is too strong. You may also make your own MQ style developer. Kodak D-49 was originally formulated for processing bromide prints though it can be used undiluted for negatives made with ordinary blue sensitive emulsions. When making alkaline developers, the ingredients should be added to the hot water in the order listed and each ingredient fully dissolved before the next is added.

D-49 Developer

   500 ml distilled water (around 120 F)
   3.1 grams metol
   45 grams sodium sulfite
   11 grams hydroquinone
   45 grams sodium carbonate
   2.1 grams potassium bromide
   Cold distilled water added to make a total 1000 ml

As with all MQ developers, metol and hydroquinone are the active developing (reduction) agents. Potassium bromide is the restrainer. Sodium carbonate is the accelerator and sodium sulfite, the preservative. If you want more density than extended development will provide, increase the hydroquinone. You may raise the pH by adding ammonia or more sodium carbonate. This is most easily done by adding drops of household ammonia. A good starting point is about 4-6 drops in 100 ml developer. Pour the developer from the developing tray into a glass beaker, add the ammonia to the developer solution and then pour the developer back into the tray. Raising the pH with ammonia or sodium carbonate will make the gelatin soften and more permeable so that the developer can be more effective, though too much will cause the emulsion to fog, lift from the glass and cause frilling.

Decreasing the potassium bromide restrainer will also cause the developer to work faster, though by doing this there is always a chance of causing fog. Tweeking the developer formula as needed eventually becomes intuitive.

Sodium Thiosulfate Fixer (working solution)
1000 ml tap water
150 grams sodium thiosulfate


APPENDIX

There are three things you will need to construct before coating gelatin emulsion plates; 2 plate racks, 2 wood leveling stands for the chilling tables and the plate drying box.

Wood Photographic Plate Racks

Vintage plate racks can be purchased at antique shops and on internet auctions, though availability is uncertain. You can make a rack by drilling holes into the top of a wooden board and fitting a series of wood dowels. The size plate you wish to coat will dictate the size of the materials. A grooved plate rack can also be made, though this type is more requires the use of a table saw.


Leveling Stands for Chilling Tables

Materials

   two 8”x8” pieces of 3/4” birch plywood
   six 1 1/2”x 5/16” bolts
   six 5/16” nuts
   six ¼” flat washers
   six 5/16” coupler nuts

A leveling stand is essentially a short adjustable tripod, with wide, flat top. Drill three 5/16” holes through the plywood. [Fig?] Countersink the holes so that the heads of the bolts sit below the surface of the plywood when installed. Install the bolts and attach the washers and nuts to the bolts on the underside of the plywood. Thread the coupler nuts on the end of each bolt. The coupler nuts allow adjustment of the leveling stand from below. The marble (or glass) chilling plate rests upon the leveling stand to complete the chilling table.


Plate Drying Box

In time you may want to make a sturdy wood box with filtered ventilation, but for your first experiments a cardboard drying box is easy to make and will do the job. You will need one, good quality, corrugated cardboard box of either double or triple wall construction and a couple extra sheets of single weight cardboard for constructing the ventilated light trap. The size of the box is dictated by the size and quantity of the plates you wish to coat in one session. While any tape will work, water soluble gummed paper backed tape (available at art supply stores) never fails over time.

Simply put, the box must allow adequate ventilation without exposure to white light. Holes must be cut into either end of the box and then fitted with a light trap as illustrated. Tape the lid closed with black tape after you fill the box with plates and for extra protection pace a piece of dark cloth over the top.


 

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