The silver gelatin dry plate process

The silver gelatin dry plate process in a nutshell: Not a printing process, like all the other liquid emulsion techniques, but an in-the-camera technique that complements the wet plate process.

Writer / Mark Scholer Pedersen

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While there has been a resurging interest in wet plate collodion photography, partly due to a rising interest in the American Civil War Era, the silver gelatin dry plate process has not received much attention. Developed in 1871, this process is far more practical than the preceding wet collodion process, and is the direct forerunner of roll film. One can pour the emulsion on the glass plate, allow it to dry, carry it about on expeditions, and develop it within a reasonable amount of time; no need for portable darkrooms, etc. This is especially practical for me because so much of my work is urban in scope (San Francisco), and a portable darkroom is pretty much out of the question.

My purpose in examining the dry plate process has been to understand and recreate the characteristic look of late 19th Century photography. Since modern emulsions are panchromatic and have anti-halation backings, among other things, their look is far different. My attempts to find a blue-sensitive film, especially one on glass, were fruitless; and so, I concluded that I would have to create my own. Once I learned that Liquid Light was in fact blue-sensitive only (and not orthochromatic) I made up my mind to proceed. Of course, the use of a ready-made emulsion is a short cut, but well worth it, especially since I have almost no working space at home in which to make my own emulsion according to original specifications. If you do, by all means, consider that the next step in bringing this process back to life.

This article is essentially a synthesis of several scattered sources; however, these other sources deal with dry plate negatives in passing only. Their main concern has been silver gelatin emulsion in all its possibilities, while my concern is specifically with the dry plate process and how it can be accomplished under difficult conditions and limited space. I don’t pretend to be the final authority in this subject, and I am aware that for every step there are alternatives; but for simplicity sake my instructions are essentially just the procedure that I use. For alternatives please feel free to experiment on your own and/or read the sources in the bibliography. This article is no more than a practical starting point.

Safety when working with the silver gelatin dry plate process

In addition to using gloves while handling photo chemicals, always keep photo utensils separate from cooking utensils.

Any container or utensil used for these chemicals should never be used for cooking afterward, no matter how much you may have cleaned them. The only exception I make is with the gelatin itself since this is a food product. I use a cooking spoon for stirring and dissolving the gelatin by itself, and another “photo” spoon for mixing it with the chrome alum hardener and Photo-Flo. Liquid Light emulsion is relatively safe, it being free of all phenols; however, it is wise to treat it with respect too, just like any other photo chemical. More the health and safety instructions.

Required items for dryplating

1. Large-format camera (at least 9x12cm/4×5″).
2. Glass plate holders (modern sheet film holders are too thin to hold relatively thick glass). These are not manufactured any more, so you’ll have to find them used. I found mine on eBay (antiques and art section). Sometimes an old camera will come with the plate holders. That’s why I bought my 1899 Adams & Westlake box camera.
3. Glass plates. They should be as thin as possible (maximum of 2mm or 1/16″). These are easy to find at any glazier shop, but will likely have to be custom-cut to fit the plate holders. Super thin, photo-grade glass is also available, but is expensive, and meant for medical/scientific use.
4. Ordinary, unflavored household gelatin, or more high-grade photo gelatin which comes in hard (250) or soft (75) bloom. Household gelatin has a bloom of about 150, and is usually less pure, and less predictable. I’ve found it very effective for the subbing layer, as long as I add chrome alum.
5. Chrome alum for hardening the gelatin. This is available at Photographers’ Formulary in the US.
   Note: formaldehyde-based hardeners, which are acidic, must not be used until the fixing stage! (see #19 below).
6. Wetting agent such as Kodak Photo-Flo.
7. Distilled water, though tap water may at times be sufficient too.
8. Liquid Light or other liquid emulsion.
   Note, I have not tried the variable contrast types yet, so I am assuming for this discussion that one is using this simple graded contrast type. Primarily designed as a print emulsion, Liquid Light seems to have an average contrast of about 3 when used in the camera. I’ve found this quite satisfactory in attaining the classic “look”, but it does mean that it has a short gray scale (see exposure below).
9. Safelight with a Kodak OC filter (amber), or 1A (red) filter.
10. Light-tight room; in my case, a very tiny closet. No running water is necessary, although it is desirable.
11. Measuring spoons or scales. Again, keep these separate from cooking utensils.
12. Stirring paddles (wooden coffee stirrers are very useful).
13. Light-tight boxes for drying the plates (printing paper boxes work well).
14. Rubber gloves.
15. Darkroom Thermometer.
16. Plastic developing trays.
17. Paper developer such as Agfa Multicontrast Developer, Neutol, or Dektol, etc.
18. Kodak hardening Fixer. Do not use rapid fixers containing ammonium thiosulfate for fixing Liquid Light. For this specific emulsion use only sodium thiosulfate (hypo) fixers. For SE-1 type emulsions (Luminos) I believe that any fixer will do.
19. General purpose hardener is recommended (to be added to the already-hardened fixer). Without hardeners the emulsion will likely lift off from the glass during development. Remember, this is not a modern, sophisticated, thin emulsion film. It swells with water during development and becomes very soft. The hardener will protect it during development.

Procedure for printing dry plates

Wear rubber gloves during this entire process in order to keep skin oil from coming into contact with the glass surfaces. This would cause resist spots where emulsion will not spread evenly.

1Washing the glass. First, scrub the glass plates using a scouring pad and powder laundry detergent. This will eliminate the layer of oily film that is usually present on glass after the manufacturing process. Notice that before washing, water will bead off the surface of the glass as it is repelled by it; but after washing the water should flow evenly over the surface. Once this is accomplished, lay the glass plates up against a vertical surface to dry. I’ve found that they don’t have to dry completely before the next stage.

2Preparation of subbing layer (done under normal lighting). It is essential that an initial subbing layer be attached to the glass, or else the emulsion layer will simply detach during tray development. Although varnish may work too, the traditional gelatin subbing layer is the most effective. In addition, it can be removed with bleach if one wishes to reuse the glass. The following recipe is what I use for a batch of four 4×5″ plates, though far more plates could be treated with this amount:

A. Heat up 50ml. of distilled water to a maximum of 50 degrees C. (about 125 degrees F.) in a beaker. Then pour 1g. (1/4 teaspoon) of chrome alum into this water and stir with a standard darkroom paddle until dissolved. Without this hardening agent the subbing layer tends to frill and sometimes completely separate from the glass during tray development; so the small expense is worth it.

B. Sprinkle 3.5g. of gelatin onto surface of 236ml. (1 cup) of distilled water. Let this stand for 10-15 minutes so that the gelatin can swell up. Then heat up the mixture until the gelatin is dissolved. Pour contents into a third container that is specified for photographic use only.

C. Add 5ml. (1 teaspoon) of chrome alum hardener solution (from step A) to gelatin solution to make a total of approximately 240ml.

D. Add approx. 15ml. (1 tablespoon) of Photo-Flo to this same mixture to make approx. 255ml. of gelatin/chrome alum/Photo-Flo solution.

E. While the solution is still warm, pour it over the glass plate and spread evenly by tilting the glass. Because it isn’t always easy to see which surface has gelatin, I go ahead and pour gelatin over both surfaces. Once this is done, carefully lean the glass against a vertical surface to dry. In order to prevent excess gelatin from collecting at the lower end I drain off most of the excess and allow the surface to cool somewhat before placing it vertically. Allow the plates to dry for at least 6-8 hours before proceeding with the next phase. The chrome alum solution (the 45ml. left over) will only keep for about a day, so it should be disposed of. Why the waste? Because I can’t measure a smaller amount accurately. I keep any left over gelatin/chrome alum/Photo-Flo solution in the refrigerator for a day or two in case I wish to make more plates. After three or more days this solution loses its beneficial properties and should be disposed of.

3Pouring on the emulsion (steps C-E under safe lighting). It is almost never necessary to use the entire contents of the emulsion during any one session, so it is recommended that only the smallest amount be heated up, and then “decanted” into smaller containers for future use. I use empty, light-tight 35mm. film canisters which hold about 30ml. each.

A. Pour 5ml. of Photo-Flo into each film canister. This will allow the emulsion to flow better over the surface of the glass by overcoming resist spots. I once tried to work without Photo-Flo just to see what would happen, and it was disastrous; live and learn.

B. Heat up a water bath to about 50C. (125F.). I often go over this amount (to about 140F.) in order to save trips back to the kitchen to reheat. A temperature control unit would be helpful here.

C. Place the container of Liquid Light upside down in the water bath and allow it to heat up. Do not shake the bottle, or else bubbles will form. Once a sufficient amount of emulsion has turned liquid, pour into the 35mm. film canisters. Close the bottle and store in refrigerator for use in the future, but try not to reheat more than three or four times, or else it will fog. The emulsion that has been decanted into the smaller canisters is meant for use either now, or in the very near future.

D. Now, place the small canisters of emulsion (with cap on tight) right side up in the water bath in order to bring the heat back up above 50C. Once this is accomplished (experience will tell you when the emulsion is liquid enough to flow well; more I cannot say), take off the cap and very carefully stir the emulsion and the Photo-Flo together with a wooden coffee stirrer. The stirring almost inevitably creates bubbles, but if done with care the bubbles are quite small and unnoticeable in smaller prints. The alternative is-from my bitter experience-very uneven distribution of the emulsion on the plate.

E. Assuming that the temperature of the emulsion has not cooled too much, you are ready to pour the emulsion on the plates. Although some have suggested heating the glass beforehand to aid in spreading the emulsion, I don’t recommend it because it may cause the gelatin subbing layer to melt. In addition, it’s an extra step in an already-complicated process. Believe it or not, I’m trying to keep this simple!

Pour the emulsion onto the center of the glass, and then tilt the glass so as to spread the emulsion over the entire surface. This is messy work. I wear gloves, pour over a developing tray, and have a towel handy. Also, newspaper spread on the floor is a good idea. However, don’t panic. Take your time. This is a learned skill that requires some practice; and besides, Liquid Light has a high tolerance for safelight. Some of the emulsion will flow onto the back side of the plate. Remove as much of this as practical. Small amounts of emulsion on the back side aren’t a serious problem, and during the development phase I scrape this excess off (see development section below).

Once the emulsion is evenly distributed over the surface I hold the plate close to the safelight to inspect it for a short period. If I see any large air pockets/bubbles, I gently blow on them until they move close to the edge of the plate. Once satisfied that I can do no better, I place the glass plate in an empty light-tight box for drying. I prefer to wait 48 hours before loading them in the plate holders (under safelighting).

Exposure of the dry plate print

Liquid Light is a slow emulsion, even compared to enlarging papers, but compared to modern film it is glacial. I started out with the assumption of a film speed of 1 ISO. Yes, 1. However, I soon found that it is closer to 1/2 ISO. This means that I give a 2 second exposure @ f/16 on bright sunny days when the subject is directly lit by the sun. The emulsion speed increases with extended drying, and I’ve found that 24 hours of drying gives me about 1/4 ISO, 48-72 hours 1/2 ISO, and five or more days brings it up to about 1 ISO.

Contrast is not significantly effected, so be extra careful with deep shadow areas; this emulsion doesn’t record well in the low registers…or the high ones, for that matter. This short gray scale is partly due to its being a print emulsion, and partly because of the short development times (well under 3 minutes) which allow little latitude for expansion or contraction.

Exposure must be accurate because you can’t overcome bad exposure during development. A more light-sensitive emulsion, and a soft-working print developer would alleviate part of this problem.

Ninety percent of the time this E.I. has worked well for me, but occasionally it hasn’t, and I regret to say I’m not always sure why. One time it was because I had allowed the plates to dry for over two weeks before exposing them, and this had fogged them. I therefore prefer to expose the plates as soon as possible.

To speed up the emulsion you may wish to heat it up to about 60 degrees C. for several hours before pouring it onto the plates. This is an option, but no more. I don’t practice it. There is the risk of damaging the emulsion, and the slow speed of 1/2 ISO is very close to what emulsions were in the 1870’s. This is actually a good thing in my opinion; for it forces the photographer to work within the constrictions of the time. You begin to truly appreciate the fine craft of early photographers.

Development of the dry plate

Since one can work under safe lighting, processing is actually very easy. Develop similar to a print: I’ve been using Agfa Multicontrast Developer, though a softer developer is likely a better choice. Try Kodak Selectol Soft, or Agfa Neutol Warm to take some of the edge off the otherwise contrasty images. Place the plates in the developer emulsion side facing upwards, and do not interleave. Use gloves, not tongs. Use a water stop bath before fixing in the hardening fixer. Adding a little bit of hardener to the fixer is a good insurance policy even though it takes longer for fixing to occur. I give 15-20 minutes of fixing as a consequence. Wash time is 40 minutes without the use of hypo clearing agent, roughly half with it. Dry as you would a print. During the wash period I scrape off any excess gelatin and emulsion off the back side of the plate. A scouring pad works well if you don’t mind putting small scratches in the glass (the scratches don’t show up in the print unless you’re enlarging to a great degree).

Printing

Most of my plates print well on a #1 or 2 filter, but this would probably be different if I used a softer paper developer during the plate processing; just haven’t gotten around to it yet. Skies pretty much always turn all white, while foreground goes dark. Thus, always expose for the ground, not the sky. Forget the sky; it’s supposed to be white, or else the print wouldn’t look Victorian! Contact prints are easy to make, but enlarging is more difficult because of the lack of proper negative carriers. I made my own out of simple cardboard, and it works perfectly fine.

Note the light areas around the trees. This is caused by light scatter from highlights into the midtones due to the lack of an anti-halation layer. Also, the white lines at the bottom of the picture are due to the emulsion lifting off during development. The use of hardeners prevents this. This is a notably contrasty subject for Liquid Light, but with some care it is still possible to print.

The darkened corners are not due to light fall-off or vignetting, but rather, to insufficient emulsion coverage. Once more, in this earlier attempt I neglected to use hardener in the gelatin, and this resulted in a lifting off of the emulsion during development. The dark spots are mostly caused by areas resistant to the emulsion. Cleanliness is a real plus! Note also the “white” boulder to the right of the picture. It is almost off the scale and would require burning-in to soften it, though little detail would be visible. However, there will almost always be some defects. Without any defects whatsoever, the final print might not look old or homemade, and that would be a shame, don’t you think?

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