Technical Information Bulletin
Updated January 9, 2003
A pH measurement determines the concentration of hydrogen ions in solution. An incorrect pH value can verify that a solution was improperly mixed; however, a correct pH measurement by itself does not ensure that a solution was properly mixed. Further testing is required.
A common problem with the pH measurement is the lack of proper maintenance of the total system. The electrodes must be calibrated for each use, and the temperature must be accurately maintained. Using the proper equipment and a fully trained technician is essential to obtaining useful results.
Specific gravity (SpGr), a unitless measure, is the ratio of the mass of a body to the mass of an equal volume of water at a specified temperature. A specific gravity measurement for a processing solution is the relative weight of a solution as compared with the density of water at 4 °C.
Density is the measurement of mass per unit volume, usually expressed in grams per milliliter.
Specific gravity measurements are useful to demonstrate that the proper dilution has been made. It provides an indication of over- or under-dilution; however, if used alone this test is not specific enough to determine whether critical components, such as developer anti-foggants, are missing or removed from the solution. Hydrometers measure specific gravity and can be purchased at a reasonable price. Be sure to measure specific gravity at the temperature at which the hydrometer was calibrated, or the measurement will be incorrect.
Matrial Safety Data Sheets are available online via the MSDS Search Page.
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Technical Information Bulletins provide information of limited or specific application. Responsibility for judging the applicability of the information for a specific use rests with the end user.