(Watercolour paint on an A4 Sketchbook page, carelessly left unattended and scribbled on by the kid)
I started trying out brush calligraphy last summer, mostly with felt-tip brush pens. The basic idea is that you go thin on the upstroke and thick on the downstroke. Once you start looking out for it, this type of writing is everywhere.
Recently I went to a 2 hour lesson by Brahmin Lettering, and that encouraged me to try brush calligraphy with watercolour paint.