Many photographers are unaware that a range of specially purified gelatins is vital to photography.
A roll of transparent, undeveloped photographic film consists of a two-sided strip of celluloid with chemical coatings on each side. There may be up to 20 or more individual layers, collectively less than one-thousandth of an inch thick. These imaging layers mainly contain sub-micron-sized grains of light sensitive silver halide crystals. When exposed to light they undergo a photochemical reaction.
In the middle of the 19th century it was discovered that gelatin was a most suitable agent for bonding these layers to the celluloid film, ensuring that the halides and other sensitizers were evenly spread, suspended and stabilised. Gelatin bonded them into a photo salt.
Silver and gelatin have since been at the heart of the fixed and moving film industry. It is why, early in the 20th century, the Hollywood movies were referred to as being shown on the ‘silver screen’.
As well as the bonding property of gelatin in making the roll of film, some of gelatin’s other versatile properties continue to be crucial to photography. After exposing the film to light and capturing the image, gelatin contributes in its development and printing.
The photographic print paper also uses gelatin-based coatings. In obtaining both the negative and then the permanent printed photograph or film, the ability of the gelatin to swell ensures the success of the photochemical reactions. In the developing and fixing baths the swollen gelatin allows chemicals access to the silver halide grains and, with fresh water, the removal of unwanted byproducts.
Present at every stage of manufacture of photographic film and printing paper—producing first the negative and then the final permanent image—is the unique and magical product of nature that is gelatin.
It is likely that few people would be aware of a connection between the photographs carried in their wallets or handbags and such things as a bowl of jelly, a marshmallow confection, a pharmaceutical capsule or the hog and cattle industries.
To date no suitable substitute for gelatin has been found in the manufacture of photographic film or paper. Gelatin for photographic use is generally made from ossein derived from bone.
The most common applications for photographic gelatins are in:
- paper (coloured, black & white)
- film (35 mm, APS, movie, art and x-ray).