Some artists and art teachers use the words ‘willow’ and ‘vine’ interchangeably to mean ‘natural stick charcoal’, some make a point to differentiate. So I usually check when talking about it if they are being specific or using a general term.
From the Nitram Charcoal people:
“Charcoal 101: Nitram vs. Willow vs. Vine Charcoal
Not all charcoal is alike and understanding the differences can make a big impact in the outcome of a drawing.”
…read the rest of their article on the Nitram Blog.
Go to the Nitram Charcoal on the Jackson’s Art Supplies website.