This is easily done by putting the plate into hot methylated spirit, and rubbing the varnish off with cotton wool.
Sea air.
It has been said that sea air affects gelatine plates, this has not been our experience.
Dirty backs.
The backs of the negatives which are generally dirty, should be cleaned by scraping, and then rubbing up with a rag moistened in hot water, or preferably, methylated spirit. The negatives should be kept in a dry place, in grooved cardboard boxes. Wooden boxes should not be used for storing either plates or negatives.
Marblings.
Are due to a dirty fixing bath; or to an uneven action of the developer arising from not rocking the plate, or to adding the alkali to the developer in the dish and not thoroughly mixing them before putting in the plate. The clearing solution removes some of these.
Prolonged and patchy fixing.
Due to the alum bath being used before “fixing” in plates from which the developer has not been thoroughly washed. It can be remedied by washing and swilling the plate in water just rendered alkaline by ammonia, and then fixing as before. We once had a plate which took several hours to fix even after this treatment.
Limpet-shell markings.