Control Procedures

Some of the many quality control factors used to monitor Hahnemühle papers are described below.

• Thickness
  Paper thickness or calibre significantly affects the feel of paper and thus the value of the work of art or the photograph. Thickness is measured with a thickness gauge and calculated at a pressure on a test area of 2 cm².

• Bursting strength
  Paper resistance to pressure applied vertically to its surface. The test area of 10 cm², stretched on a rubber membrane, is subject to a steadily increasing loading pressure. On bursting, the loading pressure is measured
  in kp/cm².

• Tensile strength (break resistance)
  Paper resistance to tensile force. An increasing vertical load is applied to a 15 mm wide and 100 mm long test strip of paper. The amount of force on breaking is the tensile strength of paper. Tensile strength is measured both in the machine direction and in cross direction.

• Smoothness
  Paper smoothness is extremely important in determining paper quality, particularly for printing papers. The reproduction fidelity of screen dots
  and color range depends on the surface's evenness in porosity.

• Gurley
  Measurement of filtration time (air permeability) of 100 ml of air at a certain pressure on a test area of 1.56 cm².

• Cobb test (water absorption)
  Paper sizing degree is determined according to the water absorption ability of a test area of 100 cm². The test area is weighed when dry. It is then subjected to 100 ml of distilled water, which is removed after 10 minutes,
  at which time it is weighed again.

• Surface pH test
  The pH value is measured with a surface electrode after a precisely defined reaction time of 1 ml of distilled water. The reaction time, i.e. the time the tested surface is exposed to water, is between 5 and 10 minutes, depending on the type of paper.

• Ink absorbency
  Paper sizing/surface properties are tested with various inks/paints (e.g. oil paint, acrylic paint and watercolor). During the test both paper ability to absorb paint and paint bleed are tested.

• Wax-pick test
  Surface resistance of sized paper to picking is tested with wax sticks of different hardness. Heated wax sticks are applied to the test area and removed rapidly after some 15 minutes.

• Ink limit
  The maximum absorbency of ink before ink dots start to become displaced.
  It is measured as a percentage of a particular color (CMYK).
  The higher the ink limit, the bigger the ink area which can be reproduced on paper. The result is good color saturation and diversity.