The Light Farm

3. Handmade Silver Gelatin Emulsions—Boiled Down Emulsion Basics

Knead the dough. Cream the shortening and eggs. Sear the steak. Even if you never set foot in a kitchen, you probably understand what those instructions mean. That's because our culture is intertwined with food. We've grown up with the vocabulary. Familiarity informs us that cooking is a thing we can do if we choose to.

It may feel as though our culture is just as intertwined with photography, but it's been a long time since most photographers made their own materials. As the processes disappeared behind factory walls, so did the vocabulary and the DIY knowledge and concept comfort. That's not actually a bad thing for us. We get to dive into a "new" photographic medium, with all the excitement and satisfaction that comes with learning something both useful and beautiful.

Making emulsions is no different from making food. A recipe is a recipe. With a few basic ingredients, a handful of vocabulary words and techniques, and a simple space to work, you can make your own black & white printing paper, dry plates, and film.

How a silver gelatin emulsion is different from other processes

Although a silver gelatin emulsion contains one or more salts, it is not a "salt print" (also called a "salted paper print"). A salt print is made by first soaking paper in a salt solution (common table salt, sodium chloride) and then drying the paper. This is followed by brushing the (literally) "salted paper" with a solution of silver nitrate before exposure. The salt and silver combine in the paper. An image takes on the texture of the watercolor paper and appears to be within, rather than on, the paper. The prints can be very lovely, but the process has inherent technical limitations. It requires strong UV light to make exposures. This makes it unsuitable for enlarging in the traditional sense. Of course, in our times of enlarged digital negatives for contact printing, this is much less an issue than it was in the past. Because the image is sunk into the paper, image fine detail can be lost. It can be difficult to achieve high contrast prints. Because it is such a slow (low ISO) process, it is not easily suitable for in-camera exposure ("paper negatives").

Adding gelatin to the mix changes everything.

A silver gelatin emulsion more precisely would be called a "silver halide in gelatin" emulsion. A halide is the active part of a salt. The type of salt determines the specific halide. For photography these are chloride, bromide, and iodide. It is the process of combining a salt with silver nitrate, while both are suspended in gelatin, that makes the magic. If we were to take a solution of salt and water and add it to a solution of silver nitrate and water, the resulting combination would drop straight out of solution (precipitate) as worthless clumps. But, add even a little bit of dissolved gelatin to either solution, or to both, and the minute crystals that form become photosensitive and stay suspended in the resulting viscous emulsion. There is a fair amount of chemistry underlying the phenomenon, but it's not something we have to understand to make emulsions, just as we don't have to understand the biochemistry of yeast to bake a loaf of bread.

With silver gelatin emulsions, a sensitized, viscous liquid is made before it is coated on paper. The emulsion, and then the image, remain on the paper surface. The image is less influenced by paper texture. Fine detail is preserved. The chemistry of the process lends itself to a variety of contrast ranges. The emulsions are capable of much higher ISO values than other traditional photographic processes. This means you can make practical enlarging paper, as well as paper negatives, film, and glass dry plate negatives.

Vocabulary confusion

As with any specialty endeavor, emulsion making has its own vocabulary. The terms may seem esoteric and daunting to the beginner, primarily because, until recently, DIY silver gelatin has been a remote concept.

Beyond the expected jargon, an additional layer of confusion arises from the early history of the technology.

George Eastman started Kodak in his mother's kitchen. This wasn't unique. Many silver gelatin materials production operations started out in a kitchen or a small home lab. Competition was fierce. Even then, from the very beginning, the individual dry plate and paper makers kept their recipes and techniques secret. This included vocabulary. Because so little information was exchanged, an emulsion maker often used his or her own in-house vocabulary. The inevitable result was the plethora of synonyms for the various steps in the emulsion making process. This is in addition to the vocabulary of analog photography and darkroom processes.

Don't try to memorize the vocabulary first thing. The easiest way to learn vocabulary is to first understand the general concepts and processes. Most of the vocabulary will just naturally fall into place. And, don't try to memorize the concepts before you start making emulsions. It's all a big, happy positive feedback loop—the more emulsions you make, the more you'll know about emulsions.

Emulsion Making Stages

It's not unreasonable that the vocabulary of the actual emulsion making is sometimes the most confusing. But take heart. Emulsion making, as with most recipes, is just a set of logically ordered steps.

Emulsification (also called Precipitation)
The first and main reaction: silver halide formation (the addition of silver nitrate to at least one salt). This step determines in large part the characteristics of the final emulsion. The gelatin used during the Precipitation step is quite naturally called the precipitation gelatin. In general, the less used, the larger the grains produced, and the faster the emulsion. Most negative emulsion recipes aim for the minimum gelatin necessary to keep the silver halides in suspension during the process. Some gelatin is necessary to keep the silver and the halide from forming big clumps that sink like so many worthless rocks.

The rate at which the silver and the halide(s) combine influences the final characteristics of an emulsion. The temperature and the percentage gelatin are both factors in the speed at which the combination takes place. All things being equal, the less precipitation gelatin used, the faster the combination, and the larger and more sensitive the grains.

Ripening (also called Physical Ripening or First Ripening)
The time the emulsion is kept at precipitation temperature beyond the actual precipitation process. The time and the temperature determine whether the emulsion will be a fine-grained slow emulsion or a larger grained faster one. You will sometimes see the entire step referred to as Ostwald ripening, although Ostwald is technically a subset process of ripening.

Second Gelatin (also called Make-Up Gelatin)
Gelatin that is added after precipitation to bring the viscosity of the emulsion up to coating weight. More gelatin can be added after the noodle washing step. This gelatin is most commonly called make-up gelatin.

Washing (also called Noodle Washing)
In washed emulsions, breaking the ripened, chilled emulsion into little pieces ("noodles", "shreds", or "worms") to facilitate washing out ammonia (if used) and excess salts that could re-crystallize on film or a plate. The washing step is not required for paper emulsions made without ammonia.

Digestion (also called Chemical Ripening, Second Ripening, or After-ripening)
At this point various additives are inserted primarily for influencing sensitivity—color sensitivity or over all sensitivity to light ("speed"). For instance, additives are necessary to make a film orthochromatic or panchromatic (i.e., sensitive to the full visible spectrum. Silver halides are naturally sensitive to only UV and blue-violet light).

Additional Vocabulary

Bloom (verb)
In a recipe it means to swell gelatin in water (soaking long enough for complete rehydration).

Shorthand for baryta-coated paper, today usually glossy. Plain, glossy commercial baryta paper gives the smoothest surface for coating. A high gloss, perfectly smooth surface is impossible to achieve without a "calendering" machine—a great beast not suitable to d.i.y. The texture of handmade baryta paper has a bit of tooth, but still gives a smoother coating surface than uncoated HP (Hot Press/smooth) watercolor paper, and is much less porous.

Bloom number
A measure of the hardness of the gelatin. Emulsion makers generally use 250 bloom (hard/photographic gelatin). A lower number is softer; a higher number is harder. 300 bloom gelatin dries to a degree of hardness that is very brittle rather than flexible.

Contact Printing and Enlarging
A contact print is made by shining light through a negative or plate that is in direct contact with the printing paper. The resulting print is identical in size to the negative. This is in contrast to "enlarging" which makes a print larger than the original negative. Contact printing requires only a light bulb and a contact printing frame. Enlarging requires an enlarger with a lens, and normally a printing easel.

Dry plate (or gelatin dry plate)
Silver gelatin negative emulsion coated on glass, dried before storage and exposure (as opposed to "wet plate", which is collodion rather than a gelatin-based process, and is exposed before the emulsion can dry).

Photographically, melted gelatin and one or more silver halides, along with any number of other specialized additions, coated and dried onto paper, glass, or film.

Emulsion vs. Colloid
By convention, the mixture of a silver halide and gelatin is called an emulsion even though it is technically a colloid—a dispersion of microscopic particles that do not fall out of suspension. Another use of the word "emulsion" is to refer to a particular film, even though technically most modern films are a mixture of more than one emulsion type.

High proof ethanol alcohol. Everclear is a brand name that has become the generic name. It is almost pure alcohol and is used as a preservative, solvent, and fuel, as well as cheap booze. Because it can be dangerous, and could be used illegally, it isn't for sale in some states in the US. Each state is different. In some states, it's sold under a different brand name, though still referred to generically as Everclear. Depending on location, Everclear (or similar) is sold only in liquor stores, either openly on the shelves, or under the front counter, available only if you ask for it. In some places, it's sold in grocery stores. It is available online. In Europe, it is referred to as 95% alcohol.

Any of the many ingredients that can be added to an emulsion immediately before coating—most often surfactants and hardeners.

On glass negatives, the emulsion lifting or floating away, usually from the edges of the plate, but also starting as bubbles anywhere on the plate. A little edge frilling will not ruin an image. The best prevention is keeping the temperatures of developer, stop, fix, and washing water all the same and around 65°F/18°C, and handling the plates gently at all times. If need be, a hardening fix can be used.

Gaslight paper
Any of a variety of very slow papers, usually AgCl. The name comes from the fact that the paper didn't require a darkroom. It could be worked in the light of a low-burning gaslight. Today, that implies a bright amber safelight, although any paper should be tested for light sensitivity. Because of their relative insensitivity (slow speed) gaslight papers are by definition contact printing papers.

The stuff that miracles are made of. Modern photographic gelatin is generally "inactive"—as close as possible to being a neutral base. "Active" gelatin is any gelatin, including food gelatin, that has not been deliberately made inactive/neutral. Using active gelatin introduces many unknowns into the system. Given the price of silver nitrate, using a known product like high-quality photographic gelatin is a very smart use of money. Photographic gelatin is usually 250 bloom, or "hard." "Soft" gelatins have lower bloom numbers. Hard gelatins set up more firmly than soft gelatins. Back in the day, emulsion makers used both hard and soft gelatins at different points in the making process. There may have been more art than science to this practice. At any rate, it is not something TLF recipes pursue. Active gelatins were also rated by their impurities that affected emulsion making. That rating system was different from the "hard-to-soft" classifications. Today, using inactive gelatins and separate additional chemicals, we can control the influences on emulsion quality and character.

An organic compound, in liquid form, which can be used to harden emulsion.

Halation and Antihalation layer
During exposure of film or glass plates, light passes through the emulsion and bounces off the substrate and back again through the emulsion. This can cause halos to form around objects => halation. Modern films have a layer that prevents the light bounce-back and eliminates halation => antihalation.

The measure of acidity (pH below 7) vs. alkalinity (pH above 7). Distilled water is the neutral baseline at 7. The "H" refers the hydrogen ion. Sometimes pH is written as p[H]. There is little reason to measure pH in the normal course of things, but inexpensive meters and/or "litmus" paper are readily available from science supply stores. pAg (and the related vAg) is the silver equivalent of the concept of pH. It refers to the concentration of silver dissolved in solution. It cannot be measured with a pH meter. Although it can be a useful measurement in complex commercial emulsion making, it is of little value to us, except for those who enjoy making d.i.y. lab equipment.

The post-exposure stages of develop, stop, fix, and wash. Fix used to be commonly called "hypo." From there, the optional step of "hypo-clear" was named. "Hypo clear" and "fix" are altogether different steps. Hypo-clear has various names—more or less describing their function—like Hypo-Wash, Orbit Bath, and Archival Wash Agent. It comes between the fix step and washing and is far more useful with paper than with film. Its use reduces wash time and conserves water, but the directions must be followed closely. With film, the last step is a wetting agent, commonly Kodak Photo-Flo or its equivalent in other brands.

The step of adding one or more extra chemicals to the emulsion to enhance the basic properties of the silver halides. This can mean speed and/or parts of the spectrum beyond UV and blue-violet. Gold and sulfur can be added to increase the speed (e.g. Steigmann's Solution). Various dyes can be added to make the emulsion orthochromatic, panchromatic, or IR (infra-red).

Silver Halides
Light sensitive compounds of silver formed during emulsion making: silver chloride (AgCl), silver bromide (AgBr) and silver iodide (AgI), often designated generically as AgX. There are any number of chemicals that can contribute the Cl, Br, or I parts of a silver halide. The "Ag" part is always from silver nitrate (AgNO3).

The term for how "fast" or "slow" an emulsion is. In modern usage this is noted by the ASA or ISO numbers. In reality, speed is not an absolute. The actual sensitivity to light of any emulsion, and most certainly handmade ones, varies with time of day, time of year, and weather conditions. It is also influenced by developer choice. Experimentation, with careful and consistent note taking, is the time-honored method of determining the actual working sensitivities of your film. ASA/ISO numbers are only the starting point.

"Subbed" (film)
From substrate; film base that has been coated with material that helps the emulsion adhere through the various processing steps.

Wetting agent. I use Photoflo 200 and/or Everclear (ethanol).

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