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The Lippmann Guide

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Though the list of chemicals and the following procedure might look daunting if you have never made a silver-gelatin emulsion before, those who have might be surprised to see that it's not all that different from your bog standard dry plate recipe.  We're just using less "stuff", and keeping the solution a lot cooler than usual.  

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Differences between my current recipe vs Darren Green's recipe

 

Over the years I have tweaked Darran's recipe (page 13 of "The True Colour of Photography), hopefully improving results.  I admit though, many of these tweaks are very much up in the air, and will be subject to changes as I learn and improve.  As I make these changes, I will update the changelog at the bottom of this page, so any experimenters revisiting this page will be able to quickly see what has changed.  However, to summarize:
 

  • Lower Precipitation Temperature

    • It was recommended to keep the solution at 35C during precipitation, however I have found that more consistent results can be obtained by lowering this, essentially as low as you can get it before the gelatin solution starts to set up.  In this case. I cool the gelatin solution to about 25C before adding in Solution B

  • Higher silver & halide salts relative to the gelatin

    • Increasing the amounts of silver nitrate and halide salts gelative to the gelatin has allowed for brighter colors, though increasing these levels too much runs the risk of encouraging grain growth and reducing saturation

  • Higher dilution

    • Originally this was intended to help keep the dilution the same as the amount of salts was increased.  However, I mostly do this now to produce a thinner layer of emulsion when coating the plates.  The thinner coating allows for quicker dry times after development.

  • Hydroquinone sensitization

    • I found that the addition of hydroquinone seems to increase the speed of the plates in the same manner as a pre-treatment in a bath of ascorbic acid.  However, it comes with the added benefit of long-term stability, as the ascorbic acid hypering step effectively puts a timer on the user to shoot and develop the plates within the next day or two.  Although my experiments with it last year yielded positive results, lately I have found that the mica plates seem to suffer from unsaturated yellow tones, so this addition will be omitted from the guide while I continue to experiment.

  • Modifying the contents of "Solution A" and "Solution B"

    • Darran's recipe recommends adding the halide salts to the silver salts, instead of the typical silver-to-halide that is used in most standard dry plate recipes.  This helps keep grain size very low and the emulsion very clear.  However, I have had issues with this producing very high contrast results and a low dynamic range.  I'm not really aware of others having this issue exactly, so it might be a "skill issue" on my part.  In my attempts to alleviate my contrast issues, I have experimented with a couple different takes on the precipitation step.

      • Reversing the Salts ("Silver into X") seems to produce more polydisperse crystal sizes, allowing for lower contrast and a better rendering of subtle colors, at the cost of a slightly cloudier emulsion.

      • Omitting Gelatin in the addition solution ("X into Silver, No Gelatin") seemed to produce a similar reduction in contrast as "Silver into X", with slightly better color saturation.  This is the method that will be detailed in this guide.

      • Doing both ("X into Silver, No Gelatin") produced by far the best dynamic range, at the cost of very cloudy plates.  Extreme halation occurs with this method, resulting in dim colors.

Comparison between "Ag into X" and "X into Ag", showing reduced contrast due to more polydisperse AgX sizes

I would encourage any would-be experimenters to not take what I have said as gospel and try different methods out for yourself - I have been known to be wrong about things with a disturbingly high frequency.​
 

Making The Emulsion

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Chemicals Required

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  • Silver Nitrate

  • Potassium Bromide

  • Potassium Iodide

  • Photographic Gelatin (200 Bloom)

  • Chrome Alum

  • Distilled Water

  • Spectral Sensitizers (choose one)

    • Set A

      • Pinacyanol chloride (1:1000 in alcohol)

      • 3,3'-Diethyl-9-methylthiacarbocyanine iodide (1:1000 in methanol)

      • 3,3'-Diethyloxacarbocyanine iodide (1:1000 in methanol)

    • Set B

      • Pinacyanol chloride (1:1000 in alcohol)

      • Erythrosine (1:1000 in distilled water)

    • Set C

      • Ethyl Violet (1:1000 in alcohol)

      • Erythrosine (1:1000 in distilled water)

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Equipment Required

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  • Beakers

    • 100mL

    • 250mL

    • 1000mL*

  • Hotplate Stirrer**

  • Digital Thermometer

  • Digital Scale (0.001g recommended)

  • Syringe with a fine tip

    • I use 60mL

  • Glass dish

  • Strainer

    • of the spaghetti variety

  • Butter knife

  • Various scoops for measuring stuff

  • Graduated cylinders for measuring stuff

    • A 1-10mL pipette will make your life way easier

  • A flatbottom metal or glass dish to use as a waterbath

    • I use a 1L Pyrex crystallizing dish

  • Red safelights

    • I use cheap RGB wifi bulbs, set to red

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* A 1000mL beaker is not strictly necessary, you just need something about that size for the emulsion to soak in

**You can get by with just a hotplate and just a magnetic stirrer, but the combo is way easier to work with

Precipitation

 

In this step, we'll be taking our silver salt and our halide salts, and reacting them together to form the light sensitive silver-halide crystals.

Solution A (250mL Beaker):

  • Distilled water (100mL)

  • Silver nitrate (1.5g)

  • Gelatin (4g)

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Solution B (100mL Beaker):

  • Distilled water (80mL)

  • Potassium Bromide (1050mg)

  • Potassium Iodide (7.5mL of 1% solution in distilled water)

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1.  Mix the two solutions as directed.  White light can be used here, as the solutions will not be light sensitive until they are mixed together.  We primarily want to avoid a silver nitrate excess, so try to be fairly precise while weighing, though +/- 5mg is acceptable.  When in doubt, err on the lower side of silver nitrate, and on the higher side of the salts.

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2.  After letting the gelatin soak for a minute or two, begin heating Solution A to 40C with gentle stirring, until all the gelatin has dissolved and the solution is clear,

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3.  Remove Solution A from heat and allow it to begin cooling off.  Add the digital thermometer probe.

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4.  Allow Solution A to cool to 25C, still with gentle stirring.  Depending on the ambient temperature of the room you're working in, this can take quite a while - I use a water bath filled with cold tap water to speed things up a bit.

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5.  When Solution A is nearing 25C, fill the syringe with Solution B.  

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6.  When Solution A has hit 25C, white lights off, red lights on.

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7.  Increase stirring speed until you can achieve a good vortex without a bunch of foam forming - I use about 500RPM

8.  With the syringe tip under the surface, slowly add B to A over about 60-90 seconds.  The solution will cloud up, but should still remain somewhat clear - with the temperature probe and magnetic stirbar still being visible.

9.  After the addition, continue mixing for a minute or two until all of our salts are nice and reacted.

10.  Pour the solution into a glass tray and set it in a refrigerator to chill.  I've got a mini fridge in my darkroom, but if you don't, you'll need to put the tray into something light-tight like a darkbag.
 

Washing

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We've now created our beautiful little silver-halide crystals, but we've also created a small amount of potassium nitrate in the process - and that needs to get removed.  Luckily, silver-halides are not soluble in water and will stay suspended in the gelatin, but potassium nitrate is - so we just need to wash the jell-o real good to remove it.
 

1.  We want to let the gelatin chill long enough to set up, but not too long - the crystals will still slowly grow due to 'Oswald Ripening', so I don't advise leaving the emulsion to chill overnight like you would with a regular emulsion.  I let mine chill for about 90 minutes or so, which is ample time for the gelatin to fully set.

2.  Take the tray out and using the butter knife, cut the gelatin into little cubes - about 1/4" or smaller if you can.

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3.  Scoop the cubes into a larger vessel - I use a 1L beaker here

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4.  Fill the beaker with distilled water, and mix the cubes around for a bit

5.  Let the cubes soak for 10 minutes

6.  Mix it around again, and then pour the solution through the strainer, catching your cubes and allowing the water to drain off

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7.  After the majority of water has drained off, take your cubes and add it to the 1L beaker again.

8.  Repeat steps 4-7 two more times, for a total of 3 changes of water.

9.  After the cubes have drained one last time, transfer them into a 250mL beaker.
 

Finals

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Now we're almost ready to melt the gelatin down and coat it on some glass, but there's a few things we'll need to be adding in first.  Silver-halides are naturally only sensitive to blue/violet/UV, so we'll need to add in our spectral sensitizing dyes to grant them sensitivity to the lower parts of the visible spectrum.  We'll also be adding in some chrome alum, which will harden the gelatin and give it better adhesion to the glass.  

For glass, I use whatever is cheap - usually single-strength from the hardware store.  I like to clean it off real nice ahead of time with some "The Works" toilet bowl cleaner, splashing the plates with some distilled water before setting them to dry to avoid any mineral deposits from the water as it dries.  
 

1.  Set your water bath temperature to 34C.

2.  Add the cubes and a stirbar to a 250mL beaker and let it start heating.  I stir pretty vigorously, at 600RPM, to try and avoid any parts of the melted gelatin from warming up too much at the bottom & sides of the beaker.

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3.  Add the temperature probe, and watch the readout like a hawk - the emulsion should melt between 29-31C
 

4.  Once the solution has melted, we can now add our spectral sensitizers.  Since this will grant sensitivity to reds, I cut down the safelights just to one bulb set to 1% brightness - enough to see what I'm doing, but not enough to really cause any fog.

These days I typically use "Set A", but you can get results with any of the sets listed, and probably other spectral dyes as well if you prefer substituting those - these are just the ones that I have tried.  Adding more of a particular dye will increase the emulsion's final sensitivity to that region, and it can be tricky getting the concentrations just right.  Increasing all dyes will help you reduce sensitivity to blues/violets.
 

  • Green

    • Erythrosine

    • 3,3'-Diethyloxacarbocyanine iodide

  • Orange/Yellow

    • 3,3'-Diethyl-9-methylthiacarbocyanine iodide

  • Orange Red

    • Ethyl Violet

  • Red

    • Pinacyanol

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In my last run, I added:

  • 2mL 3,3'-Diethyloxacarbocyanine iodide

  • 0.7mL 3,3'-Diethyl-9-methylthiacarbocyanine iodide

  • 0.75mL pinacyanol
     

You will likely need to experiment a bit empirically to determine the levels that work for you, but this should hopefully get you in the right ballpark.

5.  Add the dyes dropwise, still under vigorous stirring.  If you're using pinacyanol, you'll notice the emulsion turn quite dark

6.  Add 20mL of a 1% chrome alum solution (in water).  

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7.  Continue stirring for a minute or so, and then remove the beaker from the water bath.

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Throughout all of this, keep an eye on your temperature, and do not let it exceed 34C.  Usually all of this is performed between 32-33C.
 

The effects of various spectral sensitizers on photographic emulsions
"The Theory of the Photographic Process" (Mees, 1944)

Coating

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We're almost done, we just need to coat the emulsion on some glass and let it dry.
 

1.  Set the glass on a level surface.  It doesn't need to be perfectly level by any means, but try and get it as close as you reasonably can.

2.  Coating the emulsion can be tricky, because if you made it right, it's clear - have the safelights set to as dim as you can, while being able to comfortably see what you're doing.  I use one RGB bulb set red, 20% bright.

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3.  Measure out how much you plan on coating, and pour it in the center of the plate.  I shoot for 25mL per 8"x10" plate.
 

4.  The emulsion is quite watery, so gently tip the glass around to get as much coverage as you can.  Try and avoid using your finger to spread it around, as this can cause artifacts later on (I still do this on the edges of the plate where the emulsion stubbornly refuses to flow).

5.  Once you've coated all your plates, give them some time with the lights off to gel up again.  In colder months this takes about an hour, but during the summer, it can take closer to 3 - if it's warm in your darkroom, you might consider some gentle airflow to help them set quicker.  

6.  Once the plates have set up, set them vertical on a drying rack with airflow and let them dry for a good 8-10 hours.

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The unfortunate part about the drying process is that these plates are now absolute dust magnets, and that dust will be particularly visible when viewing the plate later on.  I used to use a bamboo dishrack with a window fan set up next to it, but nowadays I use a drying box with an air filter to help keep the level of dust at bay.
 

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