Fairly good, and a wonderful abstract drawing in and of itself, but except for your darkest areas (near black) all of your tones need to be darker by a few shades, especially in the upper half and that dark shape at the bottom that goes off the lower right corner. Even the lightest value, about a quarter up from the bottom and toward the right, should be darker.
This is good so far, but there’s more value contrast in play–especially where that large curved shape in the lower half overlaps the shapes in the upper half. It also shades toward dark much more toward the right. Except for the lightest areas, all others could be darker.
Better than the ink version in terms of value but it too should be categorically darker. Also, the texture of this drawing lacks the refinement we’re after. As shown in my demo, you need to combine strokes from all angles–these are dominantly left to right–as well as a more tempered and gentle stroke, to achieve a high resolution surface.
Better than the ink version but still under-developed. All values except for the darkest ones and the lightest ones should be darker. Note that the triangular shape on the lower right is the same value as most of the lower half, but separated from those similar values by the dark patch; its the dark patch that makes it look lighter due to simultaneous contrast, but you need to see past that by making wider comparisons.
These drawings were extremely difficult. It was incredibly hard for me to determine what shade I should make each portion of the drawing, and then it was very hard to make it that shade as well. I never knew how much was enough and no matter how long I spent, I still felt unsatisfied. That being said, I think this drawing challenged me for the better. I felt myself getting better as time went on, especially on the second drawing, and it was quite enjoyable. The pen portion was especially difficult though because I felt unsatisfied with my messy lines. I think this piece was worthwhile though and I learned a lot.