This came about whilst switching from herbal to black PETG:
A more in-depth glance:
The ones pix came about after looking to extract whatever-it-is with tweezers, so it’s indubitably one thing with the next melting level than PETG.
Taking away the (heat) nozzle with the block held in a vise unearths a tuft of one thing:
The tuft accrued a number of turns whilst unthreading the nozzle from the new finish.
Heating the nozzle a little bit extra launched the tuft:
The black-to-clear transition tailing off on the backside got here from the PETG across the tuft within the cone-shaped finish of the nozzle above the aperture. The 100 mil squares recommend the tuft used to be a definite entity, fairly than a number of threads, and may were over 5 mm lengthy.
In all probability a fraction of PTFE or every other high-melting-point plastic?
Reassemble in opposite order, reset the nozzle to Z=0 at the platform, and it’s all just right.