Glossary
Glossary
DPI (Dots-per-inch)
Generally used to describe printer resolution and often used to describe scanner resolution. The higher the number the better the resolution of the image.
Flash-Curing
Most screen printing on garments is done with wet ink going onto wet ink. Certain jobs and most dark garment prints need to have key colors (such as white) dried or cured before another color can print on-top of it. On an automatic press a flash-curing heater replaces one of the print heads. Some jobs also need a short cool-down period before the next color is printed. Flash-curing will often slow the production cycle of the job.
Halftone
A series of large and small dots that represent image areas of a continuous tone image. Continuous tone artwork can be converted into printable halftone dots using a process camera or by scanning into a computer and outputting onto film or paper as a series of dots. Even the photos in magazines are printed as a series of halftone dots. They are just smaller than we use in garment printing.
LPI (Lines-per-inch)
This actually refers to the number of dots-per-inch in a halftone but the term is LPI and NOT DPI. You can see where LPI and DPI can get confused. This term is also known as the frequency in computer graphics (frequency of lines-per-inch). The standard LPI of a screen printable design is 35 lpi to 45 lpi for cartoon type work and from 55 lpi for manual process prints to 65 lpi for automatic process prints. The higher the number the smaller the dot and the harder it is to put on a screen.
Moiré Pattern
A moiré is an interference of two patterns. It generally has a checkerboard pattern to it. You get moiré's when using patterns on patterns - as you do when you put halftone dots on screen mesh and/or halftone dots on screen mesh on a shirt pattern. Moiré patterns can be reduced or even eliminated by using a different angle (see Angles) and using a higher mesh count in relation to the LPI of the halftone. The general rule of thumb has been that to reduce moiré patterns use a mesh that is 4 to 5 times the LPI. In example, when using a 50 LPI halftone, a mesh count of 200 would be a good start. There have been lengthy articles written about moiré.
Percentage
The amount of coverage in a halftone dot is called Percentage or Tint. A 10% dot is much smaller than an 80% dot. When screen printed, a dot grows in size. This is called dot gain and it can be as much as 30% when printing on an automatic press and 40% when using a manual. For this reason you should try not to apply any tints in designs above 70% (they will just grow and be a solid). It is also important to take into account dot gain when using tints. Always use a smaller tint percentage than you think because in most drawing programs you cannot specify the dot gain (you can in Photoshop!).
PPI (Pixels-per-inch)
This is actually what a scanners resolution should be referred to. PPI is the same as DPI and you see the terms used interchangeably.
Process Color
Commonly used in offset printing, Process Printing uses the four primary colors: Cyan, Magenta, Yellow and Black - called CMYK.
Screens
Ascreen is like a printing plate. One screen is needed for each color to be printed.
Separations
Color separations of the art are needed when making screens for the job. A simple two-color design requires two separations and may take only a few minutes to create by computer. For a process color job a set of separations is generally done by a professional separator and typically costs $250.
Simulated Process (or Fake Process) Color
Real Process Color only works successfully on light shirts. Fake or simulated process color is a photorealistic look on dark garments. Most designs require flash-curing and the artwork is separated specifically for this process since designs separated for light shirts will not work on darks without extensive modification.
Special Effects Inks
These are inks that puff, feel like suede, glitter, sparkle, reflect and glow. They are generally harder to use and cost more money.
Spot Color
Solid and halftone dot printing of specific ink colors.
Underbasing
When printing on dark shirts, the print normally needs a white layer of ink under the colors to allow the colors to be bright on the garment. This layer of ink is called an Underbase. Most underbases are white and need to be flash-cured before another color can be printed on top. Some designs have more than one white underbase.