More appropriate would be to call them paintings or studies because drawings are not. But I digress...
Topic of the week: layering and line in black and white only. Vary the opacity of the layers. Do not stray into shape or pattern. Vary the lines.
As usual, I find it hard to work monochromatic. It is always a struggle to not drop some color somewhere ...
I tend to gravitate towards continuous lines that flow relatively smoothly. so I had to pay extra attention to make other types of lines.