What is underbase and why is it required for screen printing?

What is an underbase?

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. It’s a similar concept to painting a base coat of primer under your main paint color. 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 that the customer did not plan on - or one that sales did not get enough money for. However, it is essential to providing vibrant colors on a dark substrate.

Why use an underbase?

The first reason for an underbase is for color vibrancy. Although you could print each color as a high opacity ink and flash after each color, an underbase allows the print to have a bright look yet be soft to the touch because the underbase is printed through lower mesh counts and the top colors through very high mesh counts.  The second reason is color accuracy.  Printing on top of a white base will mostly eliminate the possibility of the shirt color affecting the top colors

Is underbasing required?

It depends on the design aesthetic and color of the shirt.  If the t-shirt is white or light-colored you probably can get away without an underbase and the colors will stay true.  But on darker garments, the top colors will be muted without an underbase. 

Some designers call for a “vintage” look or a “soft hand”.  In that case, an underbase may be skipped even with a dark shirt. Just keep in mind the trade-off: a softer, more lightweight print in exchange for less vibrancy and reduced color accuracy.