Screen printing with Riso stencils

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1. Screen printing with RISO masters

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Screen printing with Riso stencils
Difficulty	Intermediate
Duration	20 min.
Tools	Scissors Masking tape Medium mesh (~200 LPI) silkscreen (stretched on frame) Ink retardant Other screenprinting materials

The stencils created by the Risograph can be used with a screenprinting setup to manually press ink through the stencil. This is an alternative way of making an image for silkscreening—rather than using an emulsion-based process or another form of stencil. It also allows non-Riso inks (such as opaque whites, metallics, and other additives) to be printed, as well as printing on fabrics or other strange stocks.

Principles

This technique is dependent on three manipulations of the Risograph and the material properties of the stencil it creates:

• How stencils are normally burned and inked when printing.
• How the risograph detects whether or not there is a stencil on the drum.
• The purpose of the rice paper mesh of the stencil material.

Normal stencil making & inking procedure

The stencils created on the Risograph are usually inked immediately after the image on them is burned. The first print (the "proof print") is used to press them into the surface of the drum, which saturates them with ink. For this process though, we need to generate clean/dry stencils—so the Riso has to be manipulated into making but not inking a stencil. Since the inking happens automatically, you will need to either "block" ink from inside the drum from contacting the stencil, or try to prevent the burned stencil from ever reaching the drum.

Another basic thing to understand is the timing of the operations when making a stencil. Since duplicators were originally marketed as office equipment, one of their basic metrics was "first-print-out" time, AKA how long it takes from hitting a print button to actually having a print in hand. Both the stencil making and stencil removal process on the Risograph are quite slow, to save time, they happen simultaneously. Here's the order of operations:

1. As soon as a new stencil is sent or scanned, the Risograph will immediately attempt to remove the existing stencil, and at the same time begin burning the new one.
2. The drum spins once while the clamp is flipped open, and the old stencil peeled off the spinning drum and fed into the disposal unit (it will later be crushed into the stack of disposed stencils).
3. Meanwhile, the MMUMaster Making Unit immediately starts feeding in stencil from the roll and burning the image, from the lead edge to the trailing edge.
4. The drum cannot "receive" the stencil until the old stencil is completely removed, so the Risograph checks if it can still detect a stencil on the drum, or if anything went wrong in the stencil-removal process.
5. If the removal process was successful, the drum waits with the clamp open until the lead edge of the stencil is fed in from the MMU, then closes to grab it.
6. At this point, the image is likely still being burned, so the whole system waits for it to complete. There is a storage compartment in the MMU that the stencil fills up as it is fed and burned.
7. Once the image is complete, the drum spins once more, while a sheet of paper is fed—this prints the "proof" sheet and presses the stencil onto the drum (the proof actually prints with slightly different settings than all other prints—it prints with greater pressure, and more slowly, to try and evenly press the stencil onto the drum mesh).
8. At the end of its spin, the stencil is cut off the roll, and the machine returns to its idle state, waiting for the printing operation.

How the Riso "sees" a stencil

In order for the machine to properly place stencils on drums (and detect when something has gone wrong) it has to be able to "see" if there is a stencil on the drum or not (step 4 above). This is facilitated through a reflective sensor above the drum and the strip of black rubber tape which runs along the length of the drum, just to the right of the clamp.

At a specific angle of rotation (right when the reflective sensor is pointing at that strip), the sensor shines a light onto the surface of the drum and looks for the reflection.

1. If there is a stencil on the drum, the light will hit the shiny white surface of the stencil, and the sensor will detect the reflection.
2. If there is no stencil on the drum, the light will instead hit that black rubber strip, and no reflection will be seen.