Chemical Analysis

Chemical Analysis Figure 2-11.–Time-gamma temperature chart. line until it intersects the bold line labeled .9 (0.90 gamma). From this point, drop straight down to the time of development line and read 7.5. It takes 7 1/2 minutes of developing time at the recommended agitation. Much of the chemical analysis performed is accomplished by using common sense. Practices, such as cleanliness, accuracy, and proper preparation of solutions, should be observed at all times. Contamination can ruin a developer which, in turn, could ruin your images. Things, such as dirt and dust, in the solution can cause artifacts on the film. Before equipment is used for mixing and measuring chemicals, you should clean it thoroughly. Use a good-quality medium-strength detergent to wash glassware and other vessels. Be sure that all washed items are rinsed well with clean tap water. Keep the entire area clean to prevent contamination and ensure accuracy. Some of the more common chemical analysis methods you will use are as follows: Determining pH CHEMICAL QUALITY ASSURANCE Measuring specific gravity The equipment and methods used presently for mixing photographic solutions are the result of changes that have taken place over many years. These improvements are made to keep pace with improved sensitized materials, processing equipment, and environmental regulations. Substandard solutions make it impossible to operate a processing system within controlled limits. The preparation and use of photographic solutions must be a systematic procedure based on accurate measurement and standardized methods. High-quality standards can be achieved only when the conditions of exposure, chemistry, and processing are all within operating tolerances. Then results are predictable. In certain critical processing areas, chemical analysis is used to check solutions before and during use. This helps us to keep chemicals up to standard. Analysis of the components of processing solutions is often used as a basis for discarding solutions or adjusting their composition for future use. These procedures are used to determine proper replenishment rates to promote the efficient use of chemicals. Quality assurance procedures are implemented, so solutions are mixed, used, and discarded properly. Sensitometric testing Although there are several reasons for certifying photographic solutions, the principal objective is to get desirable, predictable, and consistent results. Control of a photographic process requires that the chemical activity of the solutions be maintained. Chemical analysis procedures used to indicate chemical activity are valuable only when the samples analyzed are representative of the processing solutions. The analysis of a sample taken improperly may do more harm than good in controlling the process. Processing solutions may be clouded or contain floating particles, dispersed oil droplets, or a precipitate. Even a clear solution may have different concentration levels in various parts of a processing tank; for instance, the chemical composition at the point where the film enters may not be the same as in other parts of the tank. To compensate for this, you must use a prescribed procedure, so all the samples are taken from the same location, such as from a point near the tank overflow. These samples should be representative of the solution at an established 2-21