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25 holography lessons

Glossary FAQ


10. Hologram development

The developer mentioned in the previous part is concentrated. The working solution is prepared directly before development. The concentrated solution is dissolved in ratio 15/400 that means 15 ml of the concentrated developer is taken for each 400 ml of the working solution. Pour 15 ml of the developer into the graduated cylinder, then pour it into the retort and dissolve with distilled water to 400 ml. Mix it thoroughly and let it stabilize for not less than 5 minutes or heterogeneity of the solution will influence on a quality of a hologram. At dissolving you may regulate temperature of the developer. It should be 18-19oC. Temperature of the fixer should be the same.
Prepare 6 trays of the corresponding size. The first tray is for the developer, the second one is for the fixer. Switch the white light off and switch the light green light on. The photoplate is not sensitive to it. Take the exposed photoplate out of the box carefully, put it in the developer with its emulsion layer upwards (!) and start your stop-watch. Put the third empty tray on the tray with the photoplate. It stabilizes the temperature and prevents accidental exposure of the photoplate. Rock the tray several times a minute. Development time of a hologram in GP-2 is 15 minutes and it is 5 minutes in GP-3 developer. It is possible to use both developers, but it seems, it is better to use GP-3 developer for the last batches of PFG-03m.
After development pour out the developer. (It cannot be used for the second time because it exhausts during work.) Move the photoplate into the washing tray for 1 - 2 minutes. Touch only edges of the photoplate! The gelatin layer swells in water and becomes very soft. The lightest touch of your fingers may cause ineradicable damage and even separation of the layer from the glass substrate.
After washing move the plate into the fixer for 1 minute and rock it each 5 - 10 seconds. After fixing has been over you may switch the white light on and wash the photoplate during 10 minutes.
While the hologram is being washed you may examine quality of its chemical processing looking at the emulsion layer color on the exposed and unexposed areas. The exposed areas of the hologram should be transparent and be light brown (see photo). Such a color of the emulsion is indication of fine-grain development, which was conducted correctly. If the hologram is absolutely transparent or it is dark brown development is not successful. Probably, concentration of the developer is not correct.

Unexposed areas of the hologram (under the piece of paper covering the front edge of the photoplate, e.g.) must be opaque and grey-green. There were no exposed microcrystals of silver bromide with the latent image centres formed on their surface. They define selectivity of the physical developer performance. As a result during developing silver atoms deposit spontaneously from the solution on casual microcrystals of silver bromide and development has chaotic unselective nature.
Therefore you should not wonder that a hologram looks opposite in comparison with usual photoplates: its exposed area is more transparent. This circumstance shows a specific nature of physical development.
The emulsion color of the unexposed areas is very important for examination of the photoplate quality. If it is grey-green, the emulsion is fresh and its fog is not substantial. If the unexposed areas are dark grey or even black the fog has intensified and selective development of even unexposed crystals is happening. It means that the photoplates begin to age and they must be turned into holograms as soon as possible. At first the fog appears on the edges of the photoplate and gradually reaches to the centre. This process is quite slow, nevertheless, it is necessary to check the photoplates periodically to control their condition.-->