Dark Brown sludge forming on nozzle

Hi all;

I’m printing in polycarbonate and I’m seeing some dark brown material forming on the nozzle (picture attached). What is it? Is it burnt polycarbonate?

Please advise, thank you.

It’s most likely old filament that has been burnt. You can just heat up the nozzle and use something to clean it. BE CAREFUL ITS HOTTTT

I have cleaned that off also by soaking just the end in acetone.

I heat mine up and use a small brass brush (from welding supply) http://www.northerntool.com/images/product/2000x2000/222/222035_2000x2000.jpg to clean it.