default brushes:
https://www.youtube.com/watch?v=uyHMXmxQdp4
how to create custom brushes:
https://www.youtube.com/watch?v=yfMDLebMwug
drawing done using the "brushed_metal" brush:
https://www.youtube.com/watch?v=HNkBXhzYGrg
drawing done using the "frog_skin" brush:
https://www.youtube.com/watch?v=Urr_UvjIdNQ