Quality Assurance Control Charts

When you are using a new developing solution, time-gamma or time-contrast index charts (as appropriate) must be developed for the variety of films to be processed in it. Given time, temperature, and agitation for each particular film in the developer, you will be able to see the results on these time charts. After the developer solution has been proven, you should process a sensitometric strip with each process- ing run. Each sensitometric strip should be read with a densitometer and plotted on the appropriate pro- cess-monitoring chart. As a minimum, you should process and plot a control strip after start-up and before shut down or at the beginning and end of each work shift. Once the densities are recorded and plotted, an accurate graphic representation of the activity of the process is provided. QUALITY ASSURANCE CONTROL CHARTS In photographic processing, control charts are used to monitor the status of specific solutions and the physical process. A list of numbers can be studied carefully to see whether they are out of line; however, when the numbers are plotted on a chart, you can see instantly whether there is data out of order. Photographic quality assurance control charts can be prepared for gamma or contrast index, minimum and maximum density (D-min and D-max), average density ( ), gross fog, temperature, pH, specific gravity, or any other variable that may be required by your quality assurance program. To be useful in your quality assurance program, you must collect and record data relative to these and other specific factors. From the recorded data, you can calculate the mean or average, and determine the upper and lower limits. If, for example, the control gamma in an aerial film processor is 1.50 and the desired average density is 1.65, you must have a method for indicating when the gamma or varies to the point where the end result is no longer desirable. When the gamma tolerance limit is ±0.05 and the tolerance limit is ±0.07, the control chart appears as shown in figure 2-12. Figure 2-12.—Control chart. 2-23