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Shown below are the definitions for: H
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hairline register Multi color printing on which misregister allowable is 1/ 2 row of dots; also the joining or butting of two or more colors, with no color overlap. See "register" and "commercial register".
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halftone The process in printing to impart tonal value to a printed piece with a single color of ink, created by separating the different tonal value areas into dots of varying size. This can create a full range of from 5 to 95% ink coverage of the paper area to be printed. The term "halftone" is used to signify any printed area that has been printed with small dots, to create a tonal effect, but technically, a "halftone" is a printed area where half or 50% of the area is covered by any number of, or sized dots of ink.
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hard bound See "case bound".
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hard sized Refers to a paper which has been heavily sized, to resist moisture penetration; opposite of slack sized.
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hard spot See "ridge".
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hardwood Source of "shorter" cellulose fibers for paper making, as extracted from deciduous or leaf bearing trees.
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headbox The first section of the paper machine, where the furnish is mixed to provide a uniform suspension to the slice for the formation of a web of paper on the wire.
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heat-set inks Inks that use as their drying mechanisms, primarily (1) the evaporation of solvents and (2) solidification, by the reduction in temperature of the thermoplastic resins in the ink vehicle. Usually associated with heat-set, web offset presses.
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hickeys When foreign material sticks to the printing press blanket or plate in an image area, it interferes with the transfer of ink to or from the blanket surface. The printed imperfection created can appear as a hickey (a white area around a dark center); can be caused by dirt on or around the press, dried ink skin, paper or coating particles, etc.
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holdout 1) In paper, the ability to resist surface liquid penetration. 2) In printing, the property of the paper to have low ink absorption, allowing the ink to set on the surface with high gloss; can create set-off with slow or poor ink setting.
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humidity See "relative humidity".
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hydration The wetting of fibers, generally to swell them, and for their increased susceptibility to refining; any process of altering fibers to increase their ability to absorb water.
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hydrometer See Baume' hydrometer; series of flotation type instruments used to measure the specific gravity or concentration of liquids.
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hydrophilic Describes the surface of a material that is easily wet by and compatible with water; "water loving"; for the opposite see hydrophobic. In offset lithography, the non-image areas of the plate are very water receptive and thus hydrophilic.
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hydrophobic Describes the surface of a material that is not easily wet by and actually repels water; "water hating"; for the opposite see hydrophilic. In offset lithography, the image areas of the plate repel water and are thus hydrophobic.
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hygroexpansivity That property of a material which causes it to expand or contract when its moisture content is changed; as in paper, when the relative humidity of the surrounding atmosphere is changed.
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hygrometer Instrument for the measurement of the relative humidity of air.
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hygroscopic That property of paper or other substance which makes it prone to absorb moisture.
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hysteresis That property of cellulose fibers, and therefore paper, that allows the percent moisture content at equilibrium with a specified relative humidity, to be dependent upon the most recent past relative humidity exposure; as if paper had a "memory", with the equilibrium moisture content closer to the most recent higher or lower relative humidity exposure, i.e., two pieces of paper that were last exposed respectively to high and low relative humidities, will have higher and lower moisture contents when brought into equilibrium at 50% relative humidity; dimensions will also vary accordingly.
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