Perfecting press A printing press that prints both sides of the paper in one pass through the press.

PH A number used for expressing the acidity or alkalinity of solutions. A value of 7 is neutral in a scale ranging from 0-14. Solutions with values below 7 are acid, above 7 are alkaline.

Photocopying An electronphotographic copying process that uses a corona charged selenium photoconductor surface, electrostatic forces and dry or liquid toner to form an image. Also known as Xerography.

Photomechanical Pertaining to any plate making process using photographic negatives or positives exposed onto plates or cylinders with photosensitive coatings.

Photopolymer coating In photo-mechanics, a plate coating consisting of compounds, which polymerise on exposure to produce tough abrasion-resistant plates capable of long runs especially when baked in an oven after processing.

Phototypesetting The method of setting type photographically.

Pica Printer's unit of measurement used principally in typesetting. One pica equals approximately 1/6 of an inch.

Picking The lifting of the paper surface during printing. It occurs when pulling force (tack) of ink is greater than surface strength of paper.

PICT A standard data format in which most Macintosh illustrations are encoded.

Pigment In printing inks, the fine solid particles used to give colour, transparency or opacity.

Pilling In printing, the building up or caking of ink on rollers, plate or blanket; will not transfer readily. Also, the accumulation of paper dust or coating on the blanket of offset press.

Pin register The use of accurately positioned holes and special pins on copy, film, plates and presses to ensure proper register or fit of colours.

Pixel In electronic imaging, a basic unit of digital imaging.

Plate cylinder The cylinder of a press on which the plate is mounted.

Platesetter Imagesetter for making plates.

Point Printer's unit of measurement, used principally for designating type sizes. These re 12 points to a pica, approximately 72 points to an inch.

Poor trapping In printing, the condition in wet printing in letterpress and lithography when less ink transfers to previously printed ink than to non-printed paper. Also called undertrapping.

Porosity The property of paper that allows the permeation of air an important factor in ink penetration.

Portrait Where the finished size is deeper than it is wide. (as in a painting).

Positive In photography, film containing an image in which the dark and light values are the same as the original. The reverse of negative.

Post Consumer Waste (PCW) Term used to describe paper which becomes waste after reaching the final consumer of the paper or paper product.

Postscript A computer description language that allows a programmer to create complex pages using a series of commands.

Postscript-compatibles Any software program that translates statements written in the Postscript page-description language. Sometime called a Postscript clone.

Pre Consumer Waste Term used to describe paper which becomes waste before the finished product reaches the final consumer of that product.

Pre-press proofs See Off-press proofs.

Presensitised plate In photo-mechanics, a metal or paper plate that has been pre-coated with a light-sensitive coating.

Press proofs In colour reproduction, a proof of a colour subject made on a printing press, in advance of the production run.

Pressure-sensitive paper Material with an adhesive coating, protected by a backing sheet until used. Also known as self adhesive, generic name Fasson.

Primary colours See additive primaries, subtractive primaries.

Print quality A term describing the visual impression of a printed piece. In paper, the properties of the paper that affect its appearance and the quality of reproduction.

Process colours In printing, the subtractive primaries: yellow, magenta and cyan, plus black in four-colour process printing.

Process lens A highly corrected photographic lens with a flat field for graphic arts line, halftone and colour photography.

Process printing The printing system using cyan, magenta, yellow and black (CMYK) to produce multi-coloured work.

Program In computers, sequence of instructions for a computer. Same as software.

Progressive proofs (progs) Proofs made from the separate plates in colour process work, showing the sequence of printing and the result after each additional colour has been applied.

PTOT Phosphorous Total amount of organic and inorganic phosphorous measured as Tot-P (phosphorous).