complete washing of the material and to control or eliminate  waste. If the wash-water temperature is allowed to drop to 65°F (18°C) or below, emulsion staining may result. As the temperature decreases, less emulsion swelling occurs, reducing the effective penetration of fresh water supplied to the emulsion. When the emulsion does not swell, the chemical-laden water does not get out through the  emulsion  surface.  These  retained  chemicals  can cause  stains. The wash water flow rate is another important factor to consider. This rate must be high enough to wash the material, but no more. When insufficient water flow is supplied  to  the  machine,  crystallized  chemicals  may  be seen  on  the  material,  and  additional  staining  can  result. You must not adjust the water flow rate higher than is needed. A few extra gallons-per-minute flow rate may not seem important; however, over time this effect can be  extremely  costly,  particularly  aboard  ship. SOLUTION   TEMPERATURE In machine processing, the temperature may vary, depending on the machine and the kind of processing being performed. High-speed processing machines operate  at  higher  solution  temperatures.  Temperature control is critical and must be maintained to produce correct results. Although this may be considered a variable   factor,   the   temperature   is   controlled automatically  by  processing  machines.  In  some machines,  the  solution  tanks  are  immersed  in  a temperature-controlled  water  jacket.  By  controlling  the water temperature within the water jacket, you can control the temperature of the solutions inside the tanks. In other machines, the solution temperature is directly controlled  by  separate  heaters  or  heat  exchange  control units in the recirculation system. A temperature probe in the  solution  tank  monitors  and  controls  the  temperature control  unit. SOLUTION  LEVELS The solution levels of a processor must be checked before processing material. If the solution level is too low, stains, improper tracking, and roller marks may affect the film or paper. When the machines are shut down for a period of time, some evaporation occurs. Since only the water from the solution evaporates, you must top off the solution tanks with water before processing material. There is a certain amount of carry-over of solution from one tank to another within the  machine.  Usually,  chemical  carry-over  is  minimized with roller squeegees. When the replenishment rate of the  processor  is  set  properly,  this  carry-over  is compensated by supplying fresh chemistry to the solution  tanks. REPLENISHMENT Most processing machines use relatively large quantities of solutions to carry out the process properly. However,  even  considering  the  large  quantities involved, certain chemical components within a given solution are used up at varying rates. In addition, there are certain reactions that form by-products that build up in the tank of the processor; for example, bromide (a restrainer)  gradually  builds  up  in  the  developing solution. Also, there is a certain amount of carry-over of solutions from one tank to another. This causes a continuous  change  in  solution  strength  and  solution purity. The replenisher solution replaces the used chemicals, dilutes the excess chemicals or by-products that have built up, and replaces the solution lost by carry-over  and  evaporation. The  replenishment  system  used  in  machine processing is called the bleed method. When the bleed system is used, a calculated amount of replenisher solution is added and forces some of the used solution out through an overflow drain in the solution tank. You must check the established replenishment rates as well as the replenisher holding tanks before and during processing.  Inconsistent  results  occur  when  the  process is not replenished correctly. DRYER  TEMPERATURE After the material is processed and washed, it continues through the machine into the drying cabinet where moisture is removed. The drying cabinet is more than a heated compartment for the processed material. In a majority of machines, both the temperature and the humidity of the cabinet are carefully controlled. Too little drying causes the emulsion to be tacky, whereas too much drying may produce excessive curl and brittleness.  Brittleness,  once  it  occurs,  cannot  be eliminated;  so  it  must  be  prevented.  Both  the temperature  and  the  relative  humidity  must  be  adjusted for the speed of the machine and the type of material being dried. Under  ideal  conditions,  the  drying  cycle  should yield a stable 50 percent relative air humidity. To lower the relative humidity of air, you must heat the air; this accelerates the evaporation of moisture. The rate of evaporation and the relative humidity are directly 10-30