There are five major steps for creating silver gelatin emulsion and I provide a good summary of each of the steps for you in this article.
STEP 1 (BE A FARMER)
We have to grow tiny light-sensitive silver-halide crystals by mixing a halide with a soluble silver salt, usually nitrate, in the presence of gelatin. In essence, we are silver halide farmers. I like how that sounds! The next time someone asks me what I do for a living, I will respond, "Thanks for asking, I am a silver halide farmer....".
How we chose to grow the crystals and the ingredients we choose ultimately determines the characteristics of the emulsion. The halide may be of an alkali metal such as sodium, potassium or an ammonium halide. In negative emulsions, some excess halide is always present.
A basic emulsion formula is AgNO3 + X => AgX + NO3. All this means is that we mixed silver nitrate (AgNO3) with a halide, and we got a new silver halide and nitrate by product. This step is referred to as precipitation or emulsification in the historic emulsion making literature.
STEP 2 (GROWTH STAGE)
Next, we allow the crystals to grow and ripen. The shape and size of the crystals form the basis of the identity of the emulsion. For example, silver bromide and silver chloride have regularly shaped crystals with few defects. The size and shape make them slow regarding light-sensitivity when compared to the addition of iodide in the very same emulsions which creates crystals with defects. These errors help increase the speed of the emulsion. Now, this is getting interesting!
Understanding photochemistry is an important part of being a crystal farmer. There is no need to be a chemist; we just need to learn the fundamentals and be excellent at controlling variables. We have the opportunity to shape the characteristics of our emulsions based on a variety of variables. From a creative perspective, I like the sound of this.
STEP 3 (CHILL OUT)
In the third step, we wash the emulsion that has been chilled and "noodled." We are removing the unwanted by-products from the crystal formation and growth stages. For negative emulsions that will be coated on film or glass plates, washing is always performed.
STEP 4 (BE SENSITIVE)
In the fourth step, we sensitize our newly grown crystals to obtain the desired response to light. Sensitization can be in the physical sense (e.g. addition of sulfur, gold, etc.) or a spectral sensitizer can be used to help our emulsion see various colors. For example, my standard negative emulsion is color blind by default (only see's UV light and blue/violet). By adding erythrosin as a spectral sensitizer, I am creating an orthochromatic type emulsion (sees everything except reds). With just one very basic modification I can completely change the feeling, mood, and aesthetic of my prints at this early stage in the overall process.
STEP 5 (PREPARE FOR LAUNCH!)
In the darkroom, we now prepare our emulsion for coating. In my case, I have an entire workflow for coating glass plates so that I can use them at a later time in the field. Can you imagine being a photographer in the late 1800s when wet plate was your primary choice? In case you don't know, you effectively have to drag a mobile darkroom with you when working with wet plate. With the invention of dry plate, this technology changed the course of photography for the next 100 years until digital technology came to life.
We have the option to add other elements such as preservatives, hardeners, anti-fogging agents, and so on.
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