I have seen on Instagram that artists are able to draw curved lines which appear as if drawn by machines.
I have also observed artists holding their pen in different ways than what is taught in schools.

[Here](https://www.instagram.com/tv/B_PM7xmn4hG/?igshid=18m2vcvx8q0xm) the artist has covered the pen by their thumb in some way.

I want to know what are the ways of holding pencils/pens for drawing are, and also what kind of grip will result in what kind of drawing.

Please add pictures too for a better understanding.