Glossary of Terms

Satellite drop

A smaller unwanted drop formed behind the main drop as it emerges from the nozzle. If it drifts away from the ink path it can cause blurred print.

Scanner

A device for converting physical images into electrical form. When most photography still used film, scanners were used from the 1960s onward to convert film images into electronic signals - analogue at first but later on to create digital files that could be stored on computers, edited in graphics programs such as Photoshop and placed into documents using layout programs.

Screen angle

In halftone printing with classic AM screens, the dot centres all align to an invisible cross-line grid, called the screen. The angle of the grid can be anything in a 360 degree rotation.

Screen mesh

In the early days of screen printing, from about 1,000 years ago to the early 20th Century, a screen printing mesh was made from silk.

Screen process

Also known as serigraphy or silk screen. A highly versatile analogue printing process, versatile enough to be used for a range of applications from fine art through to textiles, garments, signage and non-decorative industrial work such as printed electronics.

Screening

Screening is the process by which original continuous tone and multi- colour images are processed into halftones so they can be output realistically with the limited number of tones available in a printer. Nearly all printing processes use screens to reproduce variable tones.

Serigraphy

A fancier name for screen process. It's a more formally correct name than "screen process," which can become confused with halftone screens. It's also often used by the sort of art gallery that calls inkjet prints "giclée," and gravure prints "intaglio."

Solvent inks

The most common inks used for outdoor signage applications. They contain pigments suspended in volatile organic compounds (VOCs).

Spitting

Periodic automatic ejection of ink from the printheads when they are not being used, to keep the ink fresh and reduce the risk of drying in the nozzles.

Spot colour

Generally a special colour used in the printed job that cannot be achieved from standard CMYK process ink combinations. Many screen printing jobs, especially for fine art work or low value duplication, are entirely comprised of spot colours.

Squeegee

In screen printing, the squeegee is a rubber-tipped blade that is passed along the length of a screen mesh in a frame, forcing a measured amount of ink through the holes in the mesh and onto the substrate below.

Substrate

The medium that is being printed on. This can be paper, plastic, metal, wood, or virtually any other hard (and usually flat) surface. It's a generic term, used mainly because many printing processes, including inkjet and screen, can print on many different types of medium. In the signage world, the term "medium" is used more often than "substrate," but the meaning is the same. See Media.

Surface tension

The attraction between molecules at the surface of a fluid. The main significance in inkjets is the way it induces ink drops to form and contract to a roughly spherical shape as they are in flight from the head. In screen printing it is one of the factors that stops ink flowing through the holes in the mesh until forced through by the squeegee. See also Meniscus.

Swath

A band of print produced by one pass of a printhead. Larger heads can produce wider swathes so the media can be advanced more between passes if you don't need high quality.