The Risograph at the VRC, a model MH945OU, is a two-drum machine, meaning you can either print two ink colors at a time or create two masters and print colors separately.
There are two methods of printing artwork from the Risograph:
1) using digital files with special layer settings for each color to be printed
2) using the scanner bed to scan original artwork and manually combine color layers
When you're ready to duplicate an artwork, the machine will create two stencils called "masters" to produce the prints. Once the masters are set, they are applied around the drums, which hold the ink tubes. Paper is then placed in the paper tray and the machine feeds the paper, adjusting the pressure automatically depending on the weight of the paper. As the paper is passed through one or both of the ink drums it is pressed by the master proof before it comes out to the delivery tray.