How Gloss is Measured on Offset Printing Paper?

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Gloss level on offset printing paper is measured with a device called a gloss meter.  It works by sending a light source, usually at an angle of 20°, 60°, or 85° to the paper. The measurement reflected back is measured. The measurement obtained is in gloss units or GU.

 
How does it work?
The gloss meter itself has a standardized light source, a lamp, that sends a beam of light to the paper. This beam is achieved by passing through a source field and aperture stop. At exactly the same angle on the reflected side is a filtered detector. The receptor lens and detector field enable the beam to reach the filtered detector. Gloss meters are designed differently depending on the industry they provide for.

Which ones are used for printing paper?
The offset printing industry has strict standards when it comes to the gloss of paper. Painting, automotive, and flooring industries use different angles. However in offset printing, a 60° angle is the accepted standard when measuring paper.  Here is an example of one designed for measuring paper. 


Here are factors that affect the measurement value of gloss on paper:
  • How porous the paper is.
  • Amount of coating from the paper manufacturer.
  • Roughness of the printed surface.
  • Amount/color of ink on the surface.
  • Transparency of the paper.

Why do paper manufacturers make their paper glossy?
It makes the type and images sharper.  It really boils down to a compromise. 

Take posters for example.  Publishers want the pictures to be bright and vibrant to catch attention.  At the same time they do not want the strong reflection from it to prevent someone from seeing it because of it's shininess.

Magazine publishers are the same way. They want bold pictures that come from glossy paper, but they also want readers to be able to read the type. Reading a glossy magazine can be difficult depending on the angle of the light source above it.

What is a good measurement for paper?
The optimum range when measuring offset printing paper is between 60 and 95 gloss units depending on the paper and coating type. 



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