When mixing photo chemicals, you should always start with clean tools and a clean tank with the right amount of water-usually about one half to three fourths of the final volume. The temperature of the water must be as specified in the instructions. Developers are generally mixed at or about 90F to 125F, while fixers are mixed in water that should not be much above 80F.

Always dissolve or dilute ingredients in the order called for by the instructions. Dry ingredients must be completely dissolved before the next ingredient is added. All liquids must be completely diluted, while stirring, before the next ingredient is added.

After a liquid is added to a solution, rinse the bottle and add the rinse water to the solution, so all the concentrated liquid is used.

After all ingredients have been combined and thoroughly dissolved, diluted, and mixed, water should be added to bring the solution up to the correct volume. Do not forget to mix this water thoroughly into the solution.

FOLLOW DIRECTIONS

Before mixing photographic chemicals, you should read the manufacturer's directions carefully. Much research goes into the production of chemical products; however, it is only effective when the chemical is mixed and used properly. The directions for even the most familiar product should be reviewed, because there are continual attempts to improve photographic materials; for example, new film or developer combinations may call for changes in dilution, processing time, or temperature to get the required results. Learn to follow directions. This is very important in the preparation of chemicals for both quality and safety reasons.

Remember to follow the proper procedures for chemical safety. You should prepare the chemicals in a well-lighted and well-ventilated room. Do not taste or inhale any chemical. You are required to wear rubber gloves, a rubber apron, eye protection, a long sleeve shirt, and a respirator for your personal protection. Remember, for safe mixing and quality results, FOLLOW DIRECTIONS.

CAUTION

In most imaging facilities, it is common practice to connect a hose to the water spigot to aid in filling a chemical mixing tank and to prevent splashing in the sink. Aboard ship, hoses attached to potable water spigots can back siphon chemicals from the tank or sink into the drinking water supply. Such hoses should either be removed after each use or have a backflow preventor installed in the plumbing system.

CHANGING PERCENTAGES

You must know how to prepare percentage solutions from liquid chemicals. When the chemical on hand is in liquid form and of known strength, a percentage solution can easily be prepared by the following method:

Multiply the amount wanted by the strength desired and divide the product by the strength of the chemical on hand; for example, you need 11 ounces of 28 percent acetic acid. The chemical on hand is glacial acetic acid, 99.5 percent. Thus,

Add 3 ounces of 99.5 glacial acetic acid to 8 ounces of water to obtain 11 ounces of a 28 percent solution of acetic acid.