All biocides are, by definition, toxic, and the recommendations for handling them must be checked before use and the instructions followed.
For example, Formaldehyde is a toxic gas and formalin is a solution of that gas in water. All rinse baths containing formalin must have surface cover or extraction, and the area must be regularly monitored to keep the concentration of formaldehyde down below the recommended TLV (the Threshold Level Value [TLV] is a recommended level of concentration in the room air, in parts per million, above which an operator is not permitted to work for an 8 hour day).
Inspect the film under a microscope; use a needlepoint to probe out of the image area to check whether the growth is on the surface or below the surface. Gently find out if the emulsion is still firm and in good contact with the base.
If the emulsion is firm, the film should be rewashed. This usually removes all the surface growth and cleans out any grooves cut by fungi.
If the growth is all on the surface no further action will be needed except to ensure that any possible remains of the organism is dead.
There does not appear to be any method of removing hyphal strand from inside the emulsion and they may remain as a fine dried black network.
Wet gate printing has some effect on surface damage caused by fungi but there is no treatment so far known that can reduce the visual effect of fungal hyphae tunnels through the gelatine.
Several organic liquids will penetrate into these tunnels, fill them up and reduce the visual appearance to enable the film to be printed. The film has to be stored in the liquid for some days or placed in a vacuum chamber, like those used for the Vaccuumate process. The liquids that have been tried (for example at Soho Images in London) are light mineral oils like Johnson’s Baby Oil {!}. The film is then hand cleaned with 1:1:1 trichloroethane and printed by contact. The visual appearance is quite good but never perfect. The film is then ultrasonically solvent cleaned and this appears to remove the oil from the hyphal tunnels. There is no information on the long-term effect of this treatment on film and it should be regarded as a technique of last resort.
Transfer of the image to digital tape would allow the fungus image to be retouched and a new negative can then be made.
Many biocides are on the market and some, like Algezid from Agfa Gevaert, originally to prevent the growth of algae in process machine wash water, may be effective in killing fungi and bacteria. Algezid is said to have no effect on film. Many other biocides are in use throughout the world in processing machines, and the oldest, used since the earliest days of the industry is domestic bleach, sodium hypochlorite. This is very effective but is not persistent when dry.
Sodium trichlorphenolate or Morpan BC80 [Benzalkonium chloride] as a 1% solution in water are good biocides and kill any hyphae or spores and so can be used as a final rinse for almost all film as well as film with fungus or bacterial damage.
One word of warning regarding the use of special rinse baths for colour materials. Many colour films from 1955 onwards required a last rinse of a formaldehyde solution as a stabiliser and hardener. These films do not often suffer from fungi probably because they have some residual formaldehyde remaining and this is very toxic. If such a film is effected [probably due to poor control of this chemical in the original processing] the last rinse should be a solution of 6 ml of 37% Formaldehyde [Formalin] in 1L water with a drop of Photoflo to simulate the original last process stage. Formaldehyde is a very effective biocide and will protect the film from further growth. If in any doubt, this last rinse can be used for all incorporated coupler integral tripack colour films [see also the section on emulsion scratches].
Very few fungi cause illness in people but it is possible that allergies could develop in people who are sensitive to high levels of spores. Anybody with a history of lung disorders, people who are taking antibiotics and people wearing contact lenses should avoid working with fungus-infected films.
Everyone handling infected films should wear a very fine filter (down to 4 microns) full nose and mouth mask fitted with filters and prefilters. Disposable gloves and overalls should also be worn. Movement of infected films should be kept to a minimum to avoid spreading spores or infective hyphae and the films should remain in a container until needed.