The Difference and Benefits of White Underprinting and Overprinting for iColor Machines

Underprinting:

White underprinting is a technique in transfer printing where a white underbase is printed underneath the colors of a print. When printing with this method, the print is considered finished as soon as it comes out of the printer.

This is essential when printing color on dark media. If you were to print without the white underbase, the final image would look washed out. Examples for use would be clear labels, invitations on dark media, clear window cling, decals with Aqua Clear media, and much more.

The two images below showcase the difference in printing with and without the white underbase.

In the first image, a color image is printed on black paper with a white underbase. As you can see, the colors are vibrant and spot white was used as a color for the text and small white areas.

In the second image, the same colored image was printed without the white underbase. The colors are muted and appear washed out.

Overprinting:

White overprinting is primarily used when printing on transfer paper where the image is mirrored and will be pressed onto textiles or hard surfaces. In this case, the colors are printed first, and then the white layer is printed over the color image.

White overprinting can be used in a multitude of ways. When using a two step transfer paper for textiles, the adhesive is opaque white so the white toner acts as a means for a good base for the adhesive to stick to. Adhesive requires a certain density of toner for it to marry properly. Solid, dark colors are usually fine and seldomly need white, but most gradients (light colors) are often less dense, so the white is necessary to fill in the light colors and halftones. 

In this image, there is a magnification of a light green letter outlined in a yellow band. As you can see, the toner dots or pixels are used to generate the colors not on top of each other, but rather next to each other. There are gaps where very little toner is placed and require the white overprint to fill them in so the image adheres well. 

Here is the same image at a normal magnification. You can see the light green letter with a yellow outline.