Burnt blobs and black specks in the print
Plastic builds up around the nozzle, then drops brown or black lumps and specks onto the print.
Also described as burned blobs, black specks, brown spots, plastic stuck to nozzle, blob on nozzle, burnt bits, dark specks, nozzle covered in filament
Try these in order
Most likely and quickest to check first. Change one thing at a time so you know what fixed it.
Plastic collecting on the outside of the nozzle
PETG is the worst for this. Plastic sticks to the nozzle, cooks, then falls off onto the print.
- Fit a silicone sock over the heater block.
- Wipe the hot nozzle with a brass brush before each print.
- Make sure the first layer isn't so close that plastic is pushed up around the nozzle.
Burnt plastic inside the hot end
Filament left sitting hot in the nozzle for a long time breaks down and flakes off.
- Don't leave the hot end hot while idle.
- Do a few cold pulls, or replace the nozzle.
Printing too hot
- Lower the temperature by 5 to 10 °C.
Hot end blob from a failed print
A big lump of plastic round the heater block (a 'blob of death') needs cleaning off before the next print.
- Heat the nozzle to soften the lump and pick it off carefully with pliers; check the heater and thermistor wires aren't damaged.