When Does Backside Set-Off Become a Customer Complaint?
If a mirror image of the previous sheet is visible on the back, and the mirror image falls on a white background, text, or the next color, that is already a customer complaint—do not wait for the customer to unpack. If only the back of large solid areas has a layer of ink that can be felt while the white background is clean, it can be handled as a drying issue in the factory. Judge only by the back, not by how dark the front is.
A set-off from the previous sheet is visible on the back, and that set-off falls on a white background, text, or the next color—this is already a customer complaint; don’t wait for the customer to unbox it. If only a layer of ink that can be felt is on the back of a large solid area, while the white background is clean, it can be handled in-house as a drying issue. Judge only by the back, not by how dark the front is.
Why does it get on the back?
The ink hasn’t dried before the next sheet is laid on top, so ink from the front transfers to the back of the next sheet. Large solid areas, slow drying, high delivery piles, and insufficient spray powder all shorten this time. On sheetfed presses, watch the delivery pile; on web presses, watch the rewinder or the next impression, where wet ink is pressed onto the back.
A customer complaint doesn’t depend on whether you think the ink color is good; it depends on whether that set-off on the back will be seen. A faint set-off on a white background is more likely to be rejected than a thin layer of ink on the back of a dark solid.
When you must stop
| Back | Will the customer see it? | Action |
|---|---|---|
| Set-off on a white background, barcode, or text | Yes | Stop; this pile cannot go out |
| Only a thin layer of ink on the back of a solid area, with clean white edges | Usually not | Adjust spray powder, pile height, and drying; spot-check before releasing |
| Set-off has landed on the halftone dots of the next color | Yes, and it will change the color | Treat as waste; don’t just add more spray powder |
Do this first this round
- Flip through a few sheets in each pile and look specifically at the white edges on the back; don’t just look at the approved sheet on the front.
- If there is set-off on the white edges, stop. First lower the pile height and check drying, then discuss whether it can be released.
- Record the spray powder and delivery pile height at the time; next time, for the same solid coverage, use these numbers directly.
