Making the Emulsion
The process for making a Lippmann emulsion does not differ very much from a standard emulsion black & white silver gelatin emulsion. The major steps include halide precipitation, noodling & washing, and adding the finals.
My workflow currently borrows much from Darran Green's emulsion recipe, which can be found here.
1. In a 250mL beaker (Solution A), add 4g of 250 bloom gelatin and 100mL of distilled water. Allow the gelatin to swell for about 10 minutes before heating to 60C* to melt the gelatin. Take the container off heat and stir magnetically.
* - My temperature readings use a digital thermometer clothes pinned to the side of the beaker. Temperature control is very important in making this emulsion.
2. While the gelatin is cooling, measure out 700mg of potassium bromide into a 100mL beaker (Solution B). Add to it 5mL of a 1% solution of potassium iodide. Swirl to dissolve. Measure out 1g of silver nitrate. Make these measurements as accurate as possible.
3. When the digital thermometer reads that the gelatin solution is exactly 35C, pour 30 - 50mL of Solution A into Solution B. Add the silver nitrate to Solution A and continue vigorous magetic stirring. Briefly stir Solution B to ensure it is mixed.
From here on, LIGHTS OUT. A red safelight may be used.
4. Get a good vortex with the magnetic stirrer, but not so vigourously as to generate bubbles or foam. Using a fine tipped syringe, slowly add Solution B to A, with the tip of the syringe under the surface of A. The solution will cloud slighly at first, and become mostly clear again as the addition of B completes. This should take about a minute. Continue stirring for an additional minute, then pour into a container (I use a tupperware sandwich container) and place in a refrigerator* for a coule hours). Do not freeze the emulsion.
* - Do not let the gelatin be exposed to light. If you are not lucky like me and do not have a refrigerator in your darkroom, put the container in a light tight box first.
Washing the Emulsion
5. Cut the emulsion into small 1/4 inch cubes with a butter knife. Mix and strain the cubes with 3 changes of cold distilled water. Stir breifly and allow the gelatin to soak in each change for 10 minutes. When complete, strain the gelatin and add to another 250mL beaker.
Add the Finals
6. Place the beaker in a water bath, carefully controlled to be around 35C. This can take a long time, but it is crucial the emulsion does not heat higher than 35C. Use a digital thermometer to monitor the emulsio's temperature, and stir occasionally. The emulsion will liquifiy between 28C - 33C. When the emulsion is mostly liquid, heat the bath to 45C and stir the emulsion magnetically.
7. AS SOON AS the emulsion reads 35C, add the following:
0.5mL of 1:1000 erythrosine (in alcohol). This will give us additional green sensitivity.
1 mL of 1:1000 pinacyanol* (in alcohol). This will give us our red sensitivity.
2mL of a 1% chrome alum solution. This will harden the gelatin
2 drops of Photo Flo to aid in coating the plates.
These must be added under extremely subdued light.
The emulsion is ready, and must be coated immediately! Don't let the emulsion's temperature exceed 35C!
* - I've had better luck with pinacyanol, but ethyl violet may be used here instead.
Coating the Plates
The emulsion is extremely runny compared to your standard silver gelatin emulsion, which makes most hand held methods very difficult to get an even coat. I prefer to use a cheap level I purchased at the local hardware store. The level is attached to a tripod with a ball-head, and great care is taken to make sure it is exactly level.
The plates are set up on the level. After filtering the emulsion through a coffee filter, I use another syringe to dispense onto the plates; 8mL for a 4x5 and 14mL for a 5x7. The emulsion can gently be smeared with a gloved hand to ensure it covers the whole plate.
After letting the plates cool, stand them vertical and allow them to dry. A gentle fan can be used, though take care to only use a fan in a reasonably dust-free environment. I generally leave my plates to dry overnight. Once dry they can be stacked if you wish. Store in a cool, dry container and they should last several weeks (if not longer).
Exposing a Plate
"Hypersensitizing" the plates means treating them in a solution prior to exposure, rendering the plates a few stops faster (which happens to be quite a lot faster when calculating exposures with Lippmann plates!). All hypersentization techniques that do not produce fog or cause grain growth should work. Currently my favorite is a solution of TEA (triethanolamine), which seems to produce brighter results than ascorbic acid, as well as being about a 1/2 stop faster.
Try a 1% solution of TEA for 5 minutes. TEA can cause undesired swelling which will result initially in a blueshifted image after processing (though this can be remedied). Stand to dry. Generally you only want to hypersensitize on the day of shooting (though I've gone as long as a few days with no noticable issues). Update Feb. 2017: They definitely will be dim if you let them sit for two weeks before development ;)
The plate is placed in a plate holder with the emulsion facing away from the lens. I salvaged a broken plate holder, lining the back with black velvet to prevent scattered light fogging the plate.
The exposure is quite long; the rule of thumb for outdoors is 3 minutes at EV 15 and f/5.6. You will have to extrapolate even longer for indoor still lifes. My indoor exposures range from 30 minutes - 4 hours, depending on lighting and bellows extension.
I currently prefer the pyro - ammonium carbonate developer. The developer is mixed especially for each plate, and discarded when development is complete. Be careful, as this uses PYROGALLOL, which is toxic and can be absorbed through the skin (and latex!). When handling, always use nitrile gloves, eye protection, and wear a respirator when mixing the dry powder.
The developer is as follows:
60mL distilled water
2g ammonium carbonate
6 drops of 30% potassium bromide
4mL 10% solution of pyrogallol in alcohol
This developes one 4x5 plate, or a 5x7 if your tray is sufficiently
shallow. You may need more for bigger plates.
Start development at 2 minutes (at 20C) as a baseline. Developing
longer causes brighter colors but less purity (generally red/brown
cast, especially in the shadows). Cutting development yields
dimmer, more pure colors, which can be mitigated somewhat by
increasing exposure time.
There is a "sweet spot" where the colors are very pure and bright,
though this changes from batch to batch and must be determined
After development, wash for 5 minutes. Then fix in a 3% solution of hypo for 5 minutes. Wash for an additional 10 minutes after fixing.
Optional - Swelling
The final step is to swell the emulsion. Since removing the unexposed silver halide crystals during fixing causes the silver grains to move slightly closer to each other, the image will be blueshifted. Additionally, changes in humidity can cause color shifts.
Try soaking the plates in a solution of glycerin for two minutes and allowing to dry (don't wash!). If the plate is blueshifted, add more glycerin to the swelling solution and reswell. If it is red, try diluting the solution.
If there was no hypersensitization, or you hypered with ascorbic acid, start out with a 2% solution. If you hypered with a 2% solution of TEA, try starting out with a 4% glycerin solution.
A dry Lippmann plate has a sensitive surface, very susceptible to scratching or oil from grubby fingers. Cementing a prism protects the emulsion from damange and changes in humidity, while also enhancing the color reproduction by removing surface reflection.
It should be noted that dimmer plates do not seem to benefit greatly from the prism, and mounting may make them quite difficult to view. My rule of thumb thus far has been if you can see colors on the plate with ambient room lighting, you're probably in good shape to mount it.
Prisms can be either bought or made, depending on how much bang for your buck you want. Your cheapest option is to make your own -- cast some clear polyester resin (such as Eager EP-4101) between two angled pieces of glass.
Alternatively, a common shape for trophy suppliers is a wedge -- perfect for Lippmann plates! I was able to source prisms for my 4x5 plates from Noble Crystal for $13/prism, by far the cheapest from all the companies I talked to.
Blue Bridge (unmounted)
Blue Bridge (Mounted)
Forgive the blurriness, I'm still unable to get satisfactory digital recordings of my mounted plates.
Mounted on a crystal prism. Very good colors, but ultimately very dim, and requires a strong softbox to view properly.
Very bright & pure colors from this plate
5 hour exposure. Sensitized with 0.5% ascorbic acid.
A somewhat overpoweringly blue result. Possibly due to insufficient ethyl violet in this batch.
Lippmann plates are unique to color photography.
They are the only known way to permanently reproduce
a full spectrum of color. The color image can only be
viewed in relected light.
When a panchromatic fine grained black and white
emulsion is put in direct contact with a mirror, the
reflected light interferes with itself and creates an
interference pattern. The maxima of this pattern
activate the silver halides in the emulsion. When
developed, the silver in the emulsion reconstructs
this pattern when exposed to white light, giving us
a color image!
For the process to work correctly, the emulsion needs to be EXTREMELY fine grained (a "Lippmann emulsion") and transparent so that light may pass through the emulsion unaffected. This results in very long exposures.
The process also requires a mirror in direct contact with the emulsion. Traditionally mercury was used with a specialized plate holder, allowing the photographer to add mercury prior to exposure and drain it afterward. A velvet lined plate holder can also work, as the air/gelatin boundary also acts as a mirror (although colors are considerably less bright and exposures increased).
The prisms I received from Noble Crystal are a little closer to 6 degrees, than the ideal 10, though they still work fantastically (I neglected to specify a dimension for the top width, whoops).
The plates are typically cemented to the prism with Canada Balsam, which has a similar index of refraction to glass. Beware: simply mounting the plate with Canada Balsam can cause a blueshift. One can preswell and redshift before mounting to counter the blueshift, but I haven't had much luck with that. My method of avoiding blueshift is as follow:
1. Allow the plate to sit in the sun for a few hours, to harden the gelatin. The plate will brown a little, but this will not impact the colors negatively.
2. Lightly coat the plate with 3 coatings of hardware store clear acrylic spray. Allow 15 minutes at least in between coatings. Coating heavily can result in an "orange peel" look, which can be seen after mounting if one is looking for it.
Update Nov 2016: I've noticed some mild degradation in some mounted plates that possibly are caused by the acrylic layer. Additionally, none of my newly mounted plates experienced any blueshift when omitting the acrylic layer (the plates were several months old and had just been sitting in a stack). Your mileage may vary!!
Note that the acrylic spray will temporarily destroy the colors in the image. Once the plate is cemented with the canada balsam, the colors will return.
Canada balsam can take weeks to dry, so tape that bad boy up and be patient. Canada balsam is essentially very expensive tree sap, and can be very difficult to get off your fingers -- Acetone is your friend here.
When the prism is sufficiently dried, the back of the plate can be painted black. Congratulations, you have a complete Lippmann photograph!