Uncoated
Paper that has been treated with starch, or - at most - a very light pigment formula, to make its surface compatible with printing inks.

Under color removal
To improve trapping and reduce ink costs in the process color web printing, color separation films are reduced in color in areas where all three colors overprint and the black film is increased an equivalent amount in these areas.

Underrun
Term refers to an order produced or delivered that is less than the quantity specified by the customer. Allowances are permitted in trade practices for underruns.

Undertrimmed
Trimmed to a size smaller than the specified trim size.

Uniformity
Being uniform in the structure of the paper, color and finish.

Unit
Refers to the combination of inking, plate and impression operations to print each color. A four-color press has four printing units, each with its own inking, plate and impression functions.

UV
Ultraviolet radiation method of drying process color inks on high-speed multicolor offset presses.

UV coating
A very glossy, slick coating applied to the printed paper surface and dried on press with ultraviolet (UV) light. UV coating can cause slight variations in match colors, so consult an ink manufacturer or printer for best results.

UV curing
The drying of UV inks by a light reaction, rather than by heat and/or oxidation.

UV ink
An ink specially formulated to dry quickly with ultraviolet light while still on press. Fast UV drying eliminates the need to wait for the first side to dry before printing the second side. They are used extensively in screen printing, narrow web letterpress and flexographic printing.