::Hologram drying

More rapid and reliable method of the hologram drying is drying using ethyl alcohol. A research worker S. Mc Grew was one of the first who paid attention to peculiarities of alcohol drying of holograms on dichromated gelatin (DCG). He discovered that the alcohol penetrating into emulsion layer displaces water from it (this process is called "dehydratation") only in the direct vicinity from the emulsion layer surface. As though a thin "crust" of dry gelatin is formed which prevents going out and evaporation of water located inside the emulsion layer. This circumstance promotes carrying-out high-quality hologram drying.

For alcohol saving three alcohol solutions with 50%, 80% and 100% alcohol concentration are usually used. Accurately take a photographic plate from the tray with running water and after water flowing down place it into the tray with 50% alcohol solution. For removal of surface water raise one edge of the hologram from the tray under angle of 40-50 degrees and let alcohol flow down during 10-15 seconds. Alcohol drags water behind it from the photographic plate surface. If you use trays of transparent plastic you can see faint transparent inhomogeneities - swells (see photo) near the lower edge of the hologram. This is water flowed down from the photographic plate and not yet dissolved in alcohol. Having raised the photographic plate out of the tray 4-5 times in such a way you can make certain that the number of strias becomes progressively less - that is water leaves the photographic plate surface. This procedure is repeated in every tray successively raising alcohol concentration.

Immediately after termination of drying process in a 100% alcohol it's possible to remove easily the adhered small particles from the photographic plate surface using a small soft brush wetted in alcohol. This would be totally impossible before alcohol drying. The rigid "crust" prevents damage of gelatin layer. Begin to remove particles moving from the upper edge of the hologram to the lower edge following alcohol flowing down. Remove only the biggest particles since very small particle aren't visible on the hologram after alcohol drying up. Nevertheless be very careful by removal of glass splinters. The fact is that a touch of the brush can lead to a deeper penetration of the sharp glass splinter into gelatin layer. Therefore if the splinter can't be removed after several attempts leave it at its place. After alcohol drying up it possibly will create a hardly noticeable point on the hologram.

After removal of small particles place the photographic plate on the filter paper or ordinary tissue paper under an angle. So the second step of drying process begins - evaporation of water from the emulsion layer. This process is slowed down through existence of dry "crust" but since there is already no surface water and since the volume of this water considerably exceeded water volume inside the emulsion layer duration of the drying process doesn't exceed half an hour.