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DCG recipes

Weird DCG Recipes

3.6-30-467, Chromium Acetate, Ethanol Markova, Nazarova, and Sharlandjlev, “Control of the Spectral Position of DCG Reflection Holograms,” Institute of Optical Materials and Technology.

  • 64.3 g gelatin, Bloom strength of 210
  • 7.71 g ammonium dichromate
  • 0.64 g chromium acetate
  • 65 ml C2H5OH (ethanol)
  • Distilled water to make 1000 ml

Plates are coated with the solution at 50°C by doctor-blade method to 20 µm. 5-30-200, Ammonium Nitrate Bahuguna, Beaulieu, and Arteaga, “Reflection display holograms on dichromated gelatin,” Applied Optics, volume 31, issue 29 (1992).

  • 2.5 g of ammonium dichromate
  • 1.5 g of ammonium nitrate
  • 100 cc of distilled water
  • Heated to 70°C
  • 15 gm of USP grade Baker's gelatin (125 bloom strength) powder slowly added while stirring

Spin-coat at 100 rpm the still ~70°C emulsion for 90 seconds under hot-air gun. Dry vertically in a dark box. Plates are ready after about 6 hours. Sensitivity was reported as 100 mJ/cm2 at 488 nm. [In Rallison’s Thick DCG paper, he associated ammonium nitrate with hardening.] 4.5-30-500, Ammonia Coblijn, Alexander B., "Theoretical background and practical processing techniques for art and technical work in dichromated gelatin holography", SPIE Institute Series Vol. IS 8 (1990).

  • 100g water
  • 6g gelatin
  • 0.9g ammonium dichromate
  • 2ml ammonia 35% (added last) Household ammonia is typically 5-10%. [Presumably, the ammonia inhibits the dark reaction.]

DCG Notes The basic formula for dichromated gelatin is water plus gelatin plus either ammonium or potassium dichromate. The amounts of each ingredient influence the characteristics of the result. Exposure energy requirements, color shift, emulsion thickness, etc., are all impacted by the formulation. It is convenient, then, to have a standard for formula reference. Richard Rallison promoted using a system of three numbers to describe a formula—grams of dichromate, grams of gelatin, and grams (milliliters) of water. For example, 8-30-250 would be the notation for a recipe consisting of 8 grams ammonium or potassium dichromate, 30 grams of gelatin, and 250 grams of water. To make comparisons among formulae, the gelatin number is always 30 in Rallison’s notation. The three numbers can be scaled equally up or down for producing different quantities of emulsion. (Personally, I usually scale the numbers to 7.1 grams of gelatin, 7.1 grams being the mass of gelatin in quarter-ounce packet of Knox brand gelatin.) Thickness and Bandwidth The ratio of gelatin to water affects the viscosity of the emulsion, and that in turn affects the typical thickness of emulsion on the glass plate. The thickness influences the bandwidth of the final hologram. Rallison reported the following results for emulsions applied by 80 RPM spin coating method: Formula Thickness Bandwidth xx-30-350 5 – 6 µm 50 – 150 nm xx-30-250 8 –9 µm 10 – 50 nm xx-30-200 10 – 12 µm 10 – 50 nm xx-30-150 20 – 24 µm ~8 nm Replay Color Shift The ratio of dichromate to gelatin influences the color shift. The following table has typical values for exposures taken at 514 nm: Formula Color Shift 3-30-xxx 630 nm 6-30-xxx 590 nm 10-30-xxx ~514 nm Exposure Sensitivity My personal guess at typical exposure requirements for the basic recipe 8-30-300 emulsions. Wavelength Exposure 405 nm 5 mJ/cm2 442 nm 15 mJ/cm2 475 nm 40 mJ/cm2 488 nm 60 mJ/cm2 514 nm 125 mJ/cm2 532 nm 200 mJ/cm2

A great many factors may have a dramatic effect on sensitivity, notably humidity and temperature, so the above table is only a point of reference. Sensitivity also varies inversely with the dichromate concentration—halving the amount of dichromate would double the exposure requirement, for example.

General Notes “Control of DCG and non-sliver holographic materials”, SPIE volume 1600, International Symposium on Display Holography, 1991. Using 8-30-350 emulsion, exposed at 75% RH and 80 F. Wavelength Sensitivity 441 nm <1 mJ/cm^2 488 nm 4 mJ/cm^2 514 nm 50 mJ/cm^2 532 nm 100 mJ/cm^2

7.6. Sensitizer- We normally use ammonium dichromate crystals or for redder reds Potassium dichromate but the most sensitive of the dichromates (up to three times) is Pyridine dichromate. We don't use it because of its shorter life and difficult preparation. The addition of ammonium nitrate can make the dichromate several times more sensitive, but decreases the useful life and blue shifts the image. Approximate ammonium nitrate concentrations are usually in a ratio of 1 to 5 by weight to ammonium dichromate up to a maximum of 1 to 1 . When the additional substance is washed out of the gelatin a net shrinkage occurs which amounts to a blue shift in reflection holograms and lays down Bragg planes in transmission holograms.

by Joe Farina » Wed Aug 08, 2007 11:53 am There is also a paper in SPIE Institute Series Vol. IS 8 (1990) called "Theoretical background and practical processing techniques for art and technical work in dichromated gelatin holography" by Alexander B. Coblijn. This is an unusual but interesting paper based on practical experience. It is kind of an "independent viewpoint" of DCG based on holographic testing, and is not just an empty rehash of things previously published. Anyway, he used the following DCG formula: • 100g water • 6g gelatin • 0.9g ammonium dichromate • 2ml ammonia 35% (added last) I'm not sure what the concentration of ordinary household ammonia is, but that's what the above sounds like. I didn't notice a specific explanation regarding the inclusion of the ammonia, presumably it lowers the pH and increases sensitivity as Jeff explained.

Formula Characteristics xx-30-350 Thickness after spinning at 80RPM: 5-6um. Bandwidth: 50-150nm. xx-30-250 Thickness after spinning at 80RPM: 8-9um. Bandwidth: 10-50nm. xx-30-200 Thickness after spinning at 80RPM: 10-12um. Bandwidth: 10-50nm. xx-30-150 Thickness after spinning at 80RPM: 20-24um. Bandwidth: ~8nm.

3-30-xxx Replay: 630nm from 514nm exposure. 6-30-xxx Replay: 590nm from 514nm exposure. 10-30-xxx Replay: ~514nm from 514nm exposure.

Holography: A Practical Approach. Ackermann and Eichler. Page 193. Plates prepared from 7% gelatin built up on a spin table to 10-20um then dried are then sensitized in a 5% ammonium dichromate solution for 5 minutes. Wavelength Sensitivity 442 nm 10 mJ/cm^2 475 nm 80 mJ/cm^2 488 nm 100 mJ/cm^2 514 nm 250 mJ/cm^2

My personal guess at typical exposure requirements for typical 8-30-300 emulsions. Wavelength Sensitivity 405 nm 5 mJ/cm^2 442 nm 15 mJ/cm^2 475 nm 40 mJ/cm^2 488 nm 125 mJ/cm^2 514 nm 200 mJ/cm^2

DCG formulae Red-- mix 3-30-250 using Potassium Dichromate spin on at 80-90 RPM, expose single beam 90-100 mj\cmE2 @ 514 if RH = 60% and T = 70 F. Process: develop 5 min., rinse, 30 sec in 1HAB @ 120 F and .86 SG. Dry with slow pull from LHAB followed by hot air. Color should be bright Red-Orange.

Rallison’s recipe for red(-der) holograms: 200:30:3. Less AmDi = redder result. Less light = redder result. IPA:water ratio of first bath and bath duration. Longer = greater shift.

Richard D. Rallison, Ralcon Development Lab

1.3 Serendipity Back to the story, I returned to Hughes with one of Mike's broken 8 x10 inch dichromates determined to produce my own, Mike was not about to share more of his tricks of the trade so I was on my own. I coated Knox unflavored gelatin "Jello" on glass plates in my apartment using a record player built into an old steamer trunk. The dichromate processes described in the literature by Shankoff, Lin and Chang were all too time consuming to suit me. Mike had suggested during a phone conversation that I mix in all the sensitizing dichromate before coating to save some time and that helped. Everything I made initially came out milky white until I accidentally dropped an exposed plate into Milton's hardening fixer prior to soaking it in water. It was only in the fixer for 30 seconds but that proved to be sufficient to harden it enough to take the shock of hot alcohol without precipitation. A short process was immediately at hand. From then on I could make coatings on any glass surface in 5 minutes, expose them in another 5 minutes, process them in another 5 minutes and seal them up in less than 5 minutes. I immediately produced a few boxes full for show and tell and then lit the lab on fire. I managed to keep that trick under my hat until 1982, when Fred Unterseher persuaded me to publish it. I inadvertently also sold it to Steve McGrew (Holosonics) in 1979 and thought he might make it public just as I was selling it to IBM, but he never did publish. What he did publish was a very fine paper on color control in DCG in 1980, one of the first papers useful to artists working in color at the time. My method of controlling the color and clarity of master holograms was not disclosed til 1985. I dropped a developed broadband hologram into a certain bath that was about 75% alcohol and when I retrieved it and dipped it in hot dry alcohol it came back as a low scatter blue hologram. From that day in Nov 1975 I had a fast, tunable way to make bright masters that added almost no noise to the copies and so I finally had all the processes I needed to start making masters and churning out thousands of bright "dichromates" for sale. Which is what I did.