Views: 4

FILM PROCESSING

Early films were made  using a light sensitive  material coated  on a glass sheet  made to stick using a sticky material  called gelatin or collodoic  which contain  the  light sensitive silver  halide salt .

Glass sheet films were heavy and only practicable with large cameras in which they could fit. Nowadays, plastic or cellulose is the most versatile and useful for film sheets.

They are light and flexible enough to be wounded onto a spool for easier camera loading.  They are even cheaper than glass. The light sensitive chemical is coated on the front surface while its back surface is coated with anti-halation dye, which is black, and thus prevents light reflecting off the sheet into the light sensitive layer on the front surface

The gelatin materials for coating the cellulose sheet where the silver halide is coated have many advantages as a binder; it swells when paced in a development liquid. These allow the processing chemical to enter and react with the silver halide it contains.

However, when it has dried, the gelatin coating returns to its normal thickness without distorting the shape or position of the image and therefore it is most ideal for wet processing technique used in modern photography.

It takes relatively long time for light to change enough silver halide grains into metallic silver so as to form visible image (latent image) because only relatively few atoms of silver are affected by the initial exposure in the camera.

These can however be later amplified millions of times through development process using development chemicals which increase the amount of silver in those areas of the image that have been affected by light.

Three processing chemicals are needed i.e.

1. Developer solution
2. Stop bath solution
3. Fixer solution

These solutions have to be diluted with water. They are usually cheaper when bought in powder form. Most photographic chemicals deteriorate when in contact with air and therefore they must be stored in stoppered glass bottles.

Some people are allergic to some chemicals used in development and these can cause skin rashes, it is therefore necessary to use protective clothing e.g. rubber gloves.

Films are very sensitive and therefore care must be taken not to scratch them or to handle the picture area of the film particularly when it is wet or partially dry. Never expose it to dust or grits at this delicate stage.

Film processing   should be done in a   light tight closet or black fabric-changing bag.

Items used in film processing

Chemicals –

1. Developer solution
2. Fixer solution
3. Stop bath solution

Apparatus and Equipment 

The Developing Tank

These are airtight cylinders of sizes large enough to accommodate one roll of a film. There are two types of development tanks i.e. plastic and stainless steel development tank

A typical development tank has four plastic parts

• The tank body that is threaded at the top to receive the light proof lid
• The reel, which loads the film from its outer edge. It has a spiral groove designed to hold the film in the loose coil
• They have baffles in the lid which allows the solution to be poured out of the tank  without admitting any light

Agitating rod, which is a plastic rod, which dips into the hole for rotating the reel to agitate the solution.

DEVELOPING AND FIXING

Once the film is in the developing tank, the processing, the preceding processes can be carried out in the open daylight or normal light. The already diluted solution i.e. developer, stop bath and fixer solution can now be used in systematic sequence i.e.

1. Pour the solution in the tank, holding the tank at an angle to allow air to escape. Start the timer and agitate as instructed by the manufacturer. Tap the tank to dislodge air bubbles, then close the cap and then turn the tank over and back at half an hour interval throughout the development time.
2. At the end of the development time, pour the developer solution out and fill it again with the stop bath solution for 10 sec then leave the tank to stand in warm water for 1 min.
3. Pour out the stop bath; you can now use water at room temperature. Fill the tank, agitate for 10 sec empty the tank, and repeat this step again.
4. Pour in the tank and agitate once every minute. Fixing time is usually 10 min. return the fixer to the bottle. The film can now be washed.

Washing and Drying.

Washing is done using water to remove the processing chemicals, which will otherwise stain the film. Wet negatives (even when dry) are very sensitive and can easily be damaged by hairs, dust, scratches. They must therefore be handled by their edges.

Washing of films can be done in normal light but inside the developing tank. A rubber horse is used to deliver water into the tank but it is advisable to use filters in case the water has grits or sand particles.

After washing the film should be thoroughly clean, they should be dried by hanging them to dry by the clips. Remaining liquids on the surface can be dried using squeegee tongs.  

Once the film is dry, protect it as soon as possible from dust, and never fold it as these might cause scratches. A protective file is necessary at this stage for keeping or storing these films.