Most companies use dyne pens as a method to evaluate the treatment ( dyne ) levels of their materials because they are relatively cheap and easy for most operators to use. This does mean that the results can be very subjective dependent on the interpretation of each peron’s observations and can vary dependent on the application rate and pressure that is applied.
Great care must be taken not to contaminate the substrate to be tested or the pen itself with such elements as dust, wax finger prints, water and plasticizers. Water is a particular problem as every surface will have absorbed some water and like all of the other contaminents mentioned will cause incorrect readings.
All pens have a mix of two liquids to give the different dyne levels so once opened the liquids will begin to evaporate and as one usually evaporates faster
than another if the top is not kept on the pen when not in use it will quickly become inaccurate. On plastic film static electricity can also be a problem as this will also
affect the wettability of the dyne fluid and as a result can result in inaccurate results.
Surface roughness of a material can and will affect the de-wetting of the pen fluids.
The truth is all dyne levels are approximations so at least three test lines should be drawn down on the material with the first two usually being ignored to ensure that any contaminants have been flushed from the prior use of the pen.