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.
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.
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).
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.
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).