Geola supplies  a special fine-grain holographic emulsion named VRP-M, available coated either onto a glass or plastic base, for use in the HS and HS-M systems. Geola has established an international network of distributors covering most countries of the world for the supply of this material. Please contact Geola in order to find out where your nearest and most convenient supplier is located.

Below are listed typical chemical  processing schemes recommended for the production of 3D display holograms on the VRP-M material in Geola's HS-M and HS Holographic Mini-Studios.

Recommended Processing for VRP-M

The Table below shows a summary of recommended processing schemes for use with VRP-M when exposed by pulsed radiation in the green region of the spectrum.

White-light 3D holograms made on VRP-M have a natural green reconstruction colour that can be easily changed by the technique of colour - shifting using D-Sorbitol (described below).

All chemicals necessary for the preparation of the recommended solutions can be obtained from the following companies -
(i) Photographer’s Formulary Inc. - http://www.photoformulary.com/ ,
(ii) Sigma-Aldrich http://www.sigma-aldrich.com/ ,
One may also use the standard D-19 Kodak developer if 2-8g of Methyl Phenidone is added to the final solution.

The temperature of all solutions described herein is 20 ⁰C

Latensification

In order to obtain optimal sensitivity to ultra short exposures used in Holographic Mini Studios - the technique of latensification must be used.

Latensification is usually done directly after the holographic exposure. Before applying the process a latensification time appropriate for your system must be worked out. This procedure is as follows: Place a 25W white lamp at a distance of 1m from a test holoplate or film such that its light uniformly illuminates the emulsion. You will need to try several exposure times.

First of all you will need to develop the unexposed emulsion under normal safelight conditions. The plate will darken a little. This is called the “fog” level. After development wash this control plate, dry and keep it handy. Now a series of exposures with small test plates must be made. Start at about 2 secs and go up to around 10 seconds. After each exposure develop your plate and match the darkening of this plate to your control plate. If it is the same, more exposure is needed so go back and repeat the process. Stop when a result that is just marginally darker than the fog level is obtained. This is then the correct latensification exposure.

Now that the proper latensification time has been discovered, after every proper holo plate/film exposure you must take your plate and illuminate it exactly as described above for the time that you have worked out. Then all processing is as normal.

Latensification stabilizes and enhances the latent image formed by the holographic exposure. If required, chemical processing may be done with significant delay after latensification (~8 hours).

Colour Control

For the VRP-M emulsion we recommend two colour shifting techniques. One produces a fixed colour-shift towards the red of approximately 50 nm. The other produces an adjustable colour shift.

The fixed colour shifting is accomplished by soaking the final hologram for 1 minute in a bath of Potassium Iodide solution (see above). Adjustable colour shifting is accomplished by soaking the hologram for 1 minute in an aqueous solution of D-Sorbitol (sugar substitute - C₆H₁₄O₆) with added wetting agent. The colour of the final hologram depends on the solution concentration (Fig.5). After soaking, the film must be taken out and put onto a flat surface. Water drops must be removed using a rubber wiper such as a windscreen wiper. Here one must be delicate - if too much force is employed you may obtain a somewhat different colour than that predicted by Figure below. If, after drying of the hologram, the replay colour achieved is not satisfactory, the film or plate may be washed in warm water and then soaked anew in another D-Sorbitol solution of different concentration.

3D Hologram Colour versus D-Sorbitol Solution Concentration.

We would like to thank to Bernadette and Ron Olson for this colour-shifting technique as applied to the VRP-M emulsion.

1. How does refrigeration of holographic films and plates affect their lifetime?

   The practical lifetime of VRP-M plates and film at 20/25 degrees C and low humidity is more than 5 years. Rolls of film can last even longer reaching greater than 10 years. At +4 degrees C the lifetime for plates and sheet film is around 10 years.

   Note that rolls of film that have been stored for many years frequently have a 3mm-5mm stripe of damaged film at each extremity along their length. This is due to the interaction with air. Hence if your aim is to keep holographic film products for very long times it is better to stock large width rolls.

2. How do extremes of humidity and temperatures affect holographic film/plates?

   Very high humidity (>85%) should always be avoided as they will degrade the lifetime rapidly. Medium to low humidity are acceptable with low humidity being optimal. Short exposures of all materials to temperatures up to 50 Degrees C will not affect performance or greatly reduce the lifetime. Transport of the materials through hot countries is generally not a problem.

3. Is there a difference between the real lifetime of rolled and cut-sheet film material?

   Once a sheet is taken off the roll its lifetime is reduced to the published lifetime plus some period for factory storage. The roll lifetime is actually several times those published.

4. I am using the VRP-M material for making reflection holograms of 30x40cm (glass and film). I am having problems with successfully drying the emulsion. Can you help?

   Drying is a sensitive process. We recommend drying by soaking in soapy water. 1 capful of Agepon (or equivalent) per 1 liter of water works well. Be very careful to clean your film or plate meticulously before putting it in the soapy water. Any residual deposit on the emulsion can lead to severe problems. Certain chemistries will indeed produce non-soluble precipitates that need to be cleaned off by gentle and thorough wiping with a leather automobile cloth whilst the film is soaking in an (additional) bath of soapy water. Do not let any chemicals get into your final water bath as this must be completely pure. Make sure that you overdo it on the washing between processing baths and be careful you are not polluting the baths by picking up chemicals from one bath and putting them into another with your gloves or fingers (note- strong warning for your health: use gloves). Finally make sure that you take the film or plate out from the final bath slowly and in a controlled manner. The soap must be well dissolved but there should be very few bubbles. When you put the plate to dry in air, choose a quiet place that has low dust levels. Higher humidity when drying leads to taking longer to dry but to a better result.
   

5. Where can I find the relevant chemical products for holography and what equivalents can one use ?

   Chemical	Formula	"Sigma Aldrich" code	"Fluka" code	Quantity
   Agepon	AGFA wetting agent	One should find it in any local Photoshop
   Amidol	(NH2)2C6H3OHo2HCl	23,010-3	33230	2x25g
   Ascorbic acid	CH2OHCHOH(CHCOH:COHCOO)	A 7506	95212	3x250g
   Citric acid	HOC(COOH)(CH2COOH)2	C 0759	27488	2x1000g
   Cupric bromide	CuBr2		61165	1x50g
   Potassium bromide	KBr	P 9881	60095	1x1000g
   Potassium iodide	KI	P 8256	60405	2x200g
   Potassium persulphate	K2S2O8	P 9392	60490	1x500g
   Phenidone	C6H5-C3H5N2O	P 3441	79070	12x25g
   Sodium carbonate	Na2CO3	S 2127	71352	2x5000g
   Sodium hydroxide	NaOH	S 8045	71690	1x500g
   Sodium metabisulphite	Na2S2O5	S 1516	71930	2x500g
   Sodium phosphate dibasic	Na2HPO4	S 0876	71642	1x1000g

   The quantities given here are the approximate quantities you need to realize about 400 holograms 30x40cm

   Notes:
   For SM6 one may use Methyl Phenidone instead of Phenidone.

6. How many plates can be developed/bleached with a single batch of developer and bleach solution?
   
   One can develop about 1.5-2 m2 of holographic emulsion in one liter of SM-6 developer and several times more this amount of emulsion can be bleached in same bleach solution.

7. What is the shelf life of the chemicals after being mixed into solution?
   
   You can keep SM-6 during 2-3 days in a closed bottle if it was not used. But if you start to work, better to  use the same solution during one day only. The bleach is not so delicate. It is possible to use the same solution for up to 3-4 days.