Exercise: After measuring your paper control strip, fill up the empty space in the above table. Calculate the contrast as in the formula. See the example below.

Black is equivalent to paper completely exposed to ambient light. It has the maximum density. If your developer has lost some developing power, these readings will getting low. Black appears dark blue black. Use density booster to correct it.

Contrast is the ratio of high density ÷ low density. On paper measurement, colour spread and PH are not too critical because you can always use printer colour balance adjustment to correct them. However, you could save time on printer set up if you PH is always correct.

PH too high will cause magenta colour more significant. Use PH reducer to correct it. This symptom can be observed very easily on the DL measurement area. High PH will give purplish gray colour. You should get gray colour at correct PH.

PH too low will cause green colour more significant. Use PH booster to correct it. You would get greenish gray colour on the control strip. Low PH is usually caused by insufficient utilization while leaving the machine idling.

Low contrast is caused by lost of developing power. Use density booster to correct it.

Too much contrast is caused by too much developing power. Use density reducer to correct it.

Stain is on the white area. It should be as low as possible. If your unexposed portion area has yellowish colour on them. It can be caused by fog. Over developing with new chemistry without starter or over replenishment can cause fog. Use density reducer or antifog to correct it. Chemistry too dirty can also cause stain. Use chemical filter to remove the dirt.

If you lost some developing power in very short time after boosting on density. It probably is caused by too much oxidation. Use antioxidant.

By looking at the logo of the control strip. If the colours look different from what they should be. It is probably caused by insufficient bleach. This is very significant in yellow and red colour. Yellow colour will appears greenish. Red colour will appears dark red. Over bleach can cause black colour appears brown. Reduce bleach time or dilute bleach to correct it.