The principles of common cleanliness and precise measuring will prevent many chemical troubles. Without cleanliness and accuracy, many processes become guesswork.

For both personal safety and efficiency when mixing  processing solutions, there are a few commonsense rules that you must follow. Mixing chemicals is simple enough, but even a slight error can change the working characteristics of some solutions.

Chemicals should not be mixed in areas where sensitized materials are handled or stored. Chemical dust or fumes can ruin these materials. There should be adequate ventilation, a complete air change every 3 minutes, and an exhaust fan to the outside atmosphere in the area where chemicals are mixed.

CONTAINERS

Containers for photographic solutions should be made of a material that does not affect or is not affected by chemicals. Glass is the best material. Stainless steel is a highly suitable material, provided it is of the proper composition. Hard rubber and glazed earthenware may also be used satisfactorily. Acid and alkali-resistant plastic containers are acceptable.

Containers, graduates, sinks, and every utensil used in the photographic lab should always be clean. As soon as work is finished with an item of equipment, it should be cleaned and returned to its proper place. When chemicals are spilled, clean them up as soon as possible.

Chemical solutions and chemical dust corrode and cause pitting of most materials, including stainless steel, when allowed to remain for any length of time.

ACCURACY

Photographic quality suffers when the chemicals are improperly mixed. You must be certain that the amount of chemical you put into a solution is the amount specified.

The mixing of processing solutions has been greatly simplified over the years by the introduction of packaged photo-processing chemicals. Packaged chemicals come in convenient sizes for most needs. They offer standardized quality, economy, and convenience.

Packaged chemicals include film and paper developers and fixing solutions of various types that are manufactured under tightly controlled conditions. These packaged chemicals are available in either liquid or powder form. Processing solutions can be mixed easier, faster, and more accurately with packaged chemicals than with bulk chemicals.

When mixing packaged chemicals, you should always mix the entire package. Packaged chemicals usually contain more than one ingredient. During shipping and handling, these ingredients may separate with the heavier elements settling to the bottom of the package. When only part of the package is mixed, some of the ingredients that have separated or settled may not be put into the solution and the result of the process is not predictable.

MIXING

Always add chemicals to the water or solution Dry chemicals should be poured slowly into the water while it is being stirred. When preparing a developer, be careful while you are stirring so air is not beaten into the solution. When water is poured on dry chemicals, they will cake and form hard lumps that are difficult to dissolve.

Lumps or hard particles should be ground up, or crushed, with the stirring rod or with a pestle. Never add another chemical to a solution before the previous part has been completely dissolved Sometimes there is a residue that will not dissolve. The residue may be sand in the water supply, impurities in the chemicals, or other matter that found its way into the water; however, when the solution is allowed to stand for awhile, these particles usually settle and the clear liquid can be poured off. To remove sludge or dust particles that may not settle, pour the solution through a funnel containing three or four layers of cheesecloth or absorbent cotton.

Many chemicals are very sensitive to heat, and even moderate temperatures seriously affect their chemical properties. However, the rate of chemical reaction increases with an increase in temperature, and all chemicals dissolve more readily in warm water than in cool water; consequently, many formulas and instructions recommend that water as hot as 125F be used to prepare the solution that must then be cooled to the correct processing temperature. You should always try to mix solutions at the minimum temperature recommended by the manufacturer. Solutions oxidize faster at higher temperatures because of increased chemical activity at these temperatures.

When all crystals are dissolved, the solution should be practically colorless. Sometimes a solution appears cloudy or milky for a short time after it is mixed. This appearance may be caused by air taken into the solution by the dry chemicals. Air taken into a solution is distributed through the solution as tiny bubbles that cannot escape while the solution is being stirred. When the presence of bubbles has caused the discoloration, the solution will clear up when it is allowed to stand for a while. The bubbles rise to the surface of the solution and escape into the air.

Always add acid to the water. This is as easy to remember as AAA (Always Add Acid). It is dangerous to pour water into an acid. Some acids generate heat 9-8 rapidly enough to cause boiling or a splashing explosion that may splash the solution on someone nearby. Acids should always be poured slowly into a solution (near the edge of the container) while rapidly but carefully stirring the liquid.

LABELS

Mixing tanks, storage tanks, and machine tanks for developer, stop bath, fixer, and other solutions must be labeled clearly with waterproof tape or nameplates to reduce the chance of putting a solution into the wrong tank. The label should contain the name of the solution, the date it was mixed, and the name of the person that mixed it. It is also mandatory that hazardous chemical labels be attached to all chemical containers.

CONTAMINATION

All of the mixing equipment and the mixing area must be cleaned immediately after use to prevent solution contamination. The mixing tools and tanks must be thoroughly cleaned right after use to prevent dried solutions from forming encrustations that could dissolve when a new solution is mixed. Mixing tools that have not been used in some time should be washed before use to remove any dust or dirt that may have accumulated.