Drawn with a Sailor/Wancher Turquoise 1911L. The M nib on this pen comes to a sharp point which allows for some line variation not from flex but based on how deep the firm nib digs into the watercolor paper. The Noodlers Black ink is a little dry and that contributes to this effect.
An illustration copied from Dana Fox’s Watercolor with me book. I will probably be posting more of these in the future as I purchased a few of her books and they have nice sketches to copy from for practice. Done in pencil and watercolor.