Darkroom Digest: The High-Level Steps For Making Silver Gelatin Emulsions

September 24, 2016  •  3 Comments

I thought it would be a good idea to provide a high-level overview of the emulsion-making process so that in future articles the foundation will have been laid and readers can refer to this article for context.   

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EMULSION MAKING STEPS

There are five major steps to creating silver gelatin emulsion: 

STEP 1

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, the 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 a nitrate by product.  This step is referred to as precipitation or emulsification in the historic emulsion making literature. 

STEP 2

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 regular 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 the chemistry 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

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. 

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STEP 4

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

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 1800's when wetplate was your primary choice?  In case you don't know, you effectively have to drag a mobile darkroom with you when working with wetplate.  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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Tim Layton
Darkroom & Large Format Photography
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Comments

Matt McCosh(non-registered)
Great website and info. I have taken the GEH basic emulsion making course and I am now practicing at home. I'm not quite there yet making perfectly fog free images but each time I make a new batch I'm a bit better. I'd love to see more formulas and perhaps info on how they can be modified.
Tim Layton Fine Art
Hi Sasha, you are in luck. I will be publishing a lot of specific details along with videos in several upcoming articles. Stay in touch. Tim.
Sasha Krasnov(non-registered)
Hi Tim!

Want more details about mixing formulas! What part of silver nitrate, salt and gelatin perwater volume? I use Fomaspeed liquid emulsion but now moving for selfmade one.

Thank you.
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