This is Jeff Blyth’s formula for plates that exhibit an increased sensitivity to the green wavelengths 514 and 532. I have been exposing between 5 to 20mJ/cm^2 with very bright results.
First it is necessary to coat plates with an emulsion of just gelatin and water using your preferred method (veil, bar, spin etc.) followed by curing of at least 12 hours. After curing the plates can be stored indefinitely, preferably in the refrigerator and just a few can be sensitized only when needed.
To sensitize the plates, make up a solution as follows;
Weigh out in order:-
| 0.5g glycerin |
| 0.3g Aluminum Sulfate or Alum |
| 100 ml distilled or de-ionized water |
| dissolve everything up then add: |
| 5g potassium dichromate. |
Chill the solution to 5 degree C and then pour the solution into a container just larger then your glass plate.
At this point a red safelight needs to be used and the standard yellow bug light for DCG will not work.
Tilt the container to the side slightly, now take the glass and place it in the container, putting the edge in the deeper end of the liquid first and laying it down all in one motion while leveling the container. You will see the liquid slide across the top of the plate evenly.
Only leave your plate in the solution for about half a minute then shake the plate free of droplets and wipe over the glass back with a paper towel.
Stand the plates up against a wall at an angle and gently blow with a small desk fan or a hair dryer that has a cool setting until they are touch dry. At this point the alum in the formulation starts doing its job and is hardening up the coating a bit but it is only a gradual step and it is not instant.
Now your plates should be used as you normally use them, needing to be shot at once or refrigerated for later use.
You need to have your oven at 100C (212F) and have a flat clean metal plate in it so that the metal instantly heats up any dry exposed plate evenly.
I have found that for a 4x5 plate 2 minutes is a good starting point. Depending on hardness of gelatin and exposure energy you may need to adjust this time. If the plates come out milky, increase the time. For the brightest hologram keep the baking time as low as possible without the plate coming out milky.
After baking at 100C take the plate out and put it immediately onto a cold metal surface to rapidly cool the plate.
Once the plate has cooled to room temperature, process with water and alcohol just as the standard DCG would be processed but use DI water in a container as the KDi will be lost into this water. When you are finished Sodium Metabisulfite can be added to change the CrVI to CrIII which is more environmentally friendly. You may need to leave the plate in the water rinse a bit longer to get all of the potassium dichromate out depending on the thickness of your emulsion. I use two baths, one for the majority of soaking to get most of the KDi out and the second as a quick final rinse. Once you have CrIII it will then be able to be precipitated out in a saturated solution of your sodium carbonate.
An alternate drying method would be to just hit the plate with the hair dryer or other blower for just a few seconds to get the majority of alcohol off but then put the plate back into the oven at 100C until completely dry.