FIXING, WASHING, AND DRYING 407 



stainless steel, or other nonporous material. If, however, the vessels are made of 

 imglazed earthenware, wood, or other semiporous or cellular materials, some of the 

 wash solution will be absorbed by the porous material and will not be given up so 

 readily as in the case of a nonporous material. In the case of a porous container, the 

 fresh wash water will be required to wash out the solution from the pores as well as 

 from the negatives and prints. The law of washing the container is similar to that of 

 washing photographic negatives and prints, although the containers may wash more 

 slowly than photographic products. 



Temperahire of the Wash Water. — So far as removal of hypo is concerned, the tem- 

 perature of the wash water is not of great importance. But the temperature of the 

 water has secondary effects which may be quite damaging, and it is best to keep the 

 temperature of the wash water within certain limits, if this is at all possible. 



As gelatin is warmed, it swells and finally, at sufficiently high temperatures, flows 

 off its support. For this reason, the temperature should not become excessively high. 

 A good general rule to follow is to keep the wash water between 60 and 70°F. whenever 

 this is possible. For those cases in which it is not possible to keep the temperature of 

 the wash water down to these limits, damage of the film may often be prevented by 

 hardening the gelatin in a hardening bath. Sudden changes in the temperature of the 

 gelatin are likely to cause wrinkles or reticulation. For this reason it may be advisable 

 to keep the temperature of the wash water as near the temperature of other solutions as 

 possible. 



Hypo Eliminators. — To reduce the washing time required to eliminate hj^po from 

 negatives and prints, it has been suggested that the hypo be converted into some 

 substance which can be more easily washed from the gelatin. There appears to be 

 little advantage in using such hypo eliminators, however, for then the "hypo elimina- 

 tor" must be removed from the gelatin, and the removal of this substance may take 

 as long as the removal of the original hypo. 



Drying. — Ordinarilj'' the drying of photographic negatives and prints is not given 

 serious consideration. In spite of the fact that comparatively little, if any, physical 

 action takes place which may harm the materials during drying, certain practices are 

 to be preferred to others. 



Mechanism of Drying. — Although drying is often treated as an operation involving 

 only a single step, two distinct phases of drying take place. The first of these is con- 

 cerned with the removal of excess surface water; the second phase is one of evaporation 

 of the remaining water much of which has been absorbed by the gelatin. In the second 

 phase, evaporation takes place normally, or it may be accelerated through the use of 

 forced-draft air blasts. Washes in alcohol or other liquids of low vapor pressure, and 

 consequently having rapid evaporation, also result in accelerated drying. 



Removal of the excess surface water is desirable for two reasons. In the first place 

 it speeds up the total time required for drying by removing large drops or pools which 

 would otherwise be required to evaporate. In the second place the tendency of the 

 unremoved water to form water spots resulting in certain forms of spots or stains is 

 greatly removed. The excess water may be removed from negatives and prints by 

 blotting them with a soft but lintless cloth or absorbent material. In this case the 

 cloth should be free from woven pattern, as otherwise the pattern may be impressed 

 on the soft gelatin. Another very satisfactory way of removing excess surface water 

 is to blot or rub off the water with viscose sponges. In this case care must be used, 

 especially with miniature films, to see that small particles of the sponge do not become 

 loose and deposit themselves on the film, where they might remain to produce spots on 

 the final print. 



After the surface water has been removed, the negatives or prints may be hung 

 up to dry by evaporation. Drying may take place through the normal evaporation. 



