Formic Aldehyde Frilling
its name. This has been recommended as preservative of pyro, and we have found that half an ounce of dilute formic acid will preserve i oz. of pyrogallol even when exposed to light and air for over two months, but when mixed with the accelerator the developer turns thick and muddy more rapidly than plain pyro.
Formic Aldehyde. See Formalin.
Formulae, Chemical. See Equivalence, Chemical.
Freezing Mixtures. See Cooling and Freezing.
Frilling. By this is meant the gelatine leaving the plates in folds or wrinkles. It usually begins at the edges, and occurs chiefly when fixing, but often during development or washing. The causes are numerous, but as most of these are but slightly under the control of the operator they will only be enumerated, and the possible cures given at length. The chief cause is the use of a gelatine of too horny a nature, and possessing but little tenacity.. Again, long-continued boiling of an emulsion especially tends to this evil; an improperly washed plate, unequal drying, and excessive slowness of the emulsion* in setting, due to the use of a soft gelatine or the heat of the weather, or by allowing too forcible a stream of water to impinge upon the edge of a plate, or the use of an exceeding strong developer, or the differing temperatures and densities between the developing, fixing, and washing fluids. The use of formalin is one of the most com-plete preventives of frilling. (See Formalin.) When a batch of plates purchased is found to be subject to frilling, they may be kept for two or three months, when the fault will often be eradicated; but where this remedy is impracticable, or, by reason of the number of the plates being but small, is hardly desirable, the following immediate steps may be taken, or Formalin (q.v.) may be used. The plate, before development, may be coated with collodion made as follows : -
When this is used, the plate, after being collodionised, must be well washed with clean water till it no longer repels water