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Updated 18 Febr. 2010

Y – 1) One of the three CIE tristimulus values, equal to the luminous reflectance or transmittance; the green primary. 2) Spectral colourmatching function of the CIE standard observer used for calculating Y tristimulus value. 3) One of the CIE chromaticity coordinates calculated as the fraction of the sum of the three tristimulus values, attributable to the Y value.

Yankee machine – Paper machine with a single large drying cylinder (Yankee cylinder) which represses the paper and produces a glazed surface on one side.

Yellow – One of the process ink colours for printing. Pure yellow is the “blueless” colour; it absorbs all wavelengths of blue from light and reflects all red and green wavelengths.

Yellowing (aka Brightness Reversion) – Describes a transformation inherent to all vegetable fibres which is caused by aging. Yellowing is very evident in groundwood papers. (e.g., only a few hours in direct sunlight is enough to yellow a newspaper).

Yield – Amount of product obtained from a process in relation to the amount of raw material used.

Yield Point – The stress at which a material begins to plastically deform. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

Young’s Modulus of Elasticity – Describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain. Because all other elastic moduli can be derived from Young’s modulus, it is often referred to simply as the elastic modulus. Young’s modulus is a mathematical consequence of the Pauli exclusion principle.

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