Fashion Terms — the Apparel Search fashion terminology directory
An underbase is a layer of ink — generally white or another light color — printed as a base on a dark shirt for the other colors to sit on, giving the top colors more brilliance. Because the underbase is a high-opacity ink, it is flash-cured before the top colors are printed over it. Underbases are also called an underlay, a very common alternate name, or a mask. The trade-off is real: underbasing slows production and is often an extra color, which costs more money.
This term is relevant for screen printers that are printing on “dark” color garments.
An underbase is a layer of ink (generally white or other light color) that is printed as a "base" on a dark shirt for other colors to sit on. This gives the top colors more brilliance. Since the underbase is generally a high opacity ink, it is flash-cured before the top colors are printed over it. Not only does underbasing slow production, but it is often an extra color (which costs more money). Underbases are also called an underlay (very common) or a mask (not as common).
Tips of screen printing on dark colored fabrics:
1. light color inks on dark goods generally require a base white screen and a flash.
2. Designs that have white in the image will only need a flash.
3. Any fluorescent inks need a white underbase+flash
Here are the reasons:
Shirts are fabric, and when ink is layered on it soaks into the fabric resulting in a muted look. Flash curing dries the ink enough to lay a second coat on top of the first coat (instead
of the fabric) resulting in a brighter color. Note that the ink also will feel thicker, because it is. Another reason for flashing is dye migration. This is most often seen on red shirts as the dyed
color of the shirt (especially with white ink) tends to “migrate” through the ink and turn it pink. Flashing reduces this dramatically.
There is no underbasing without a flash-cure unit (or some other method to flash dry the fabric). If you plan to do a lot of flashing make sure the unit is large enough to meet your production capacity.
You should position the flash unit so that you can get a cure in a matter of seconds. Plastisol will cure to the touch at around 120 degrees C (consult with your flash unit manufacturer for proper temperature suggestions based on their machine). If you fully cure the fabric, the top colors may not adhere properly and can flake off when washing the shirt. The length of time for the curing process is critical.
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You may also want to learn about direct to garment printing machinery and processes.
It is important to know proper Underbase & Flash
The underbase is a screen of its own, so it belongs in the job plan from the start: one extra screen to make, register and clean, one flash step between the base and every color that follows, and a slightly heavier hand to the finished print. Designs that already contain white need only the flash, because the white in the image does the underbase's work. Fluorescent inks always need a white underbase plus flash, since fluorescent pigments are translucent by nature and cannot cover a dark ground on their own. Light inks on dark goods follow the same rule as the general case: base white screen first, flash, then color.
There is no underbasing without a flash-cure unit or another method of flash-drying the fabric, so shops that print dark garments regularly should size the unit to production capacity and position it so a cure takes a matter of seconds. A flash that is too slow becomes the bottleneck of the whole press run; a flash that runs too hot or too long fully cures the base and invites the adhesion failure the temperature guidance warns about. The working window is narrow by design — dry to the touch, not cured through — and experienced printers test it on a scrap garment whenever the garment color, ink or room conditions change.
Shirts are fabric, and ink layered directly on fabric soaks in and looks muted. A flash-cured underbase gives the top colors a smooth ink surface to sit on instead of the fabric, so the printed colors come out brighter — at the cost of a thicker-feeling print.
The tendency of a shirt's dye — most often seen on red shirts — to migrate up through the ink and tint it, turning white ink pink. Flashing the underbase reduces dye migration dramatically.
Plastisol cures to the touch at around 120 degrees C, but the flash should only dry the ink enough for the next coat — if the underbase is fully cured, the top colors may not adhere properly and can flake off in the wash. Consult the flash unit manufacturer for the right settings for the machine.