A pencil lead is a type of ceramic.
It is made with mixing clay with graphite and baking it at high temperature.
These vessels are made with the same recipe as a pencil lead. So they are not only ceramic vessels but also tools for drawing.

The special way of baking makes the white part normal ceramic and makes the black part a pencil lead. So the user can grab the white part and can use the pencil without making a hand dirty.