Mottling is the uneven appearance, mostly in solid areas: small dark and light areas appearing in the surface of paper (board) caused by ink, paper or press work. As this definition says mottle is influenced by many parameters: type of ink, colour sequence, construction of printing press, speed, rubber blanket, damping water and the most important one: the type of paper. Variations in the surface characteristics as absorption and smoothness play an important role in the mottle and are caused by the production process and the components in the paper. There can be three kinds of mottle:

• Back trap (print) mottle: an uneven printing result, caused by uneven ink absorption of the paper.

• Water interference mottle: an uneven printing result, caused by insufficient and uneven water absorption of the paper, followed by uneven ink absorption. 

• Ink trap mottle: an uneven printing result, caused by a wrong trapping of the ink in tack and/or viscosity and is also influenced by an uneven absorption of the ink by the paper. 

Principle

A paper is printed several times under standard conditions with an IGT printability tester. The result is observed as a degree of unevenness in the print quality. This can be done visually in comparison with a self made scale or other papers and with an analysing system.

Method of operation

• It is recommended to execute the test in the standard atmosphere; to most standards it is 23.0 ± 1.0 °C (73.4 ± 1.8 °F) and 50 ± 2% rh.

• For the operation of the AIC2-5T2000, Global Standard Tester, High Speed Inking Unit 4 and ink pipette follow the instructions of the manuals, IGT information leaflet W100 and the displays accurately.

• Handle the samples carefully.