The RISO printer may look like a photocopier or laser printer but it is quite different. It prints one color at a time using a disposable screen created internally when a print is sent to it. This is more like a silk screen process than other types of printing like laser printing which melts plastic toner onto the page or inkjet printing which sprays dots of liquid ink onto the page. The RISO printer squeezes ink through the mesh of the generated screen onto the page.
This is a drum for red ink and one of the screens that wraps around the drum. The ink from the inside of the drum gets squeezed through the screen onto the paper as it moves through the printer
Screen with image clogging the holes in the screen that block the ink: light areas are the open screen holes the ink can pass through to the paper
To print in any color you have to both purchase a drum that is used for that color and the ink that you put in the drum. You also have a roll of screen paper that gets pulled onto the drum with the image applied. When you go to print the next image, the previous screen gets trashed and put in a waste container for disposal.
As well as the standard black drum and ink, we have blue, yellow and red drums and inks.
We can only print these colors and any combinations made with them.
Note: not CMYK typically used by printers to create a wide range of colors – so we cannot make some colors. Also blending colors is very difficult: see the other page about what is appropriate to print on the RISO and what doesn’t work well.