Dampening solution analysis
for offset printing

Water hardness

The lime content of water can cause problems during printing. For example:

• Bare running of the ink rollers (limescale deposits)
• Deposits on the rubber sheet
• Influence on the pH value
• Fluctuations in the pH value

Excessively high amounts of chloride, sulphate or nitrate also encourage corrosion. 

Test strips can be used to easily determine the overall hardness of the water: briefly dip the hardness testing strips into the water and read off the results around two minutes later.

pH value

“pH” comes from the Latin Potentia hydrogenii and represents the logarithmic representation of the hydrogen ion concentration. The pH value is therefore a measured value for determining the acidic or alkaline behaviour of aqueous solutions. It is not possible to determine which type of acid or alkali is involved. A liquid with a pH value of 5 has ten times more acid in it than a liquid with a pH value of 6. Generally speaking, dampening solution additives are buffered in order to neutralise external influences as much as possible

Conductance value = µS/cm

The conductance value describes how current is conducted in a liquid. Impurities in the dampening solution will cause the conductance value to rise. The conductance value varies, depending on the water and additive. The conductance value must be tested and serves as a guide parameters. The temperature and alcohol concentration also influence the conductance value. The higher the isopropanol (IPA) content, the lower the conductance value. Modern conductance value measuring equipment factors the temperature into the measurement. It is important that the conductance probe in the central dampening solution system is cleaned and calibrated on a regular basis.

The conductance value should be determined with “freshly prepared dampening solution”, so that it can serve as the “yardstick” when changing the dampening solution. If the conductance value in the dampening solution has risen by around 1,000 µS/cm, this should be regarded as the trigger to change the dampening solution. To prevent printing problems, it is recommended that the dampening solution be replaced at regular intervals. The use of optional dampening solution filters (e.g. Softflow) allows the shelf life of dampening solutions to be increased significantly.

A universal testing device allows the pH value, temperature and conductance value to be measured. All electronic measuring devices must be calibrated regularly.

Plate wetting

Checking the alcohol

The alcohol used should be very pure. This can be checked with a simple test: add equal parts of water and alcohol to a clean glass. After 30 to 45 minutes, the liquid should be clear. If the liquid is cloudy, the alcohol should not be used.

Reading off the hydrometer

The measuring spindle must always be able to float freely in the glass cube or similar. There must be no air bubbles in the liquid or on the measuring

spindle. Transparent liquids are read “at the bottom”. Read off the measured value at Vol. % and the temperature, and calculate with the Vol. % value. The calculated value is then verified against the table.

The hydrometer can be used to determine the IPA content in water. The device shows the percentage by volume and weight. Essentially, percentages by volume should be measured. Temperature has an important role to play in IPA determination. Therefore please note the temperature comparison. Include the specific weight (density) of the dampening solution additive in the calculation.

Alcohol measurement

Alcohol is conventionally measured in the dampening solution central system using the density of the dampening solution (float). The density of the dampening solution is now determined by the IPA content, however, but also by the temperature, the nature of the additive and the degree of contamination. Regular cleaning is essential in this context. Modern measuring methods such as infra-red or ultrasound measurement are largely unaffected by external influences.