Adding structures to paintings

Since I had these two tests on my wall I thought it was worthwhile adding structures to them.

The first one I did on the left, I used white charcoal to map out the shape using three point perspective and then went over the white with black ink.
It was the first time I decided to make it look as if the structure was appearing and disappearing behind paint strokes, with the intention of giving the paint strokes depth.
The ink doesn’t sit well at all on top of the oil paint but for an experiment that doesn’t matter to me, plus the cracking of the ink gives the structure an interesting texture.
I actually liked the shape better before I added the black ink.
The clean white lines of the charcoal works well against the dark background in contrast to the loose painterly marks.

So for the second experiment I decided to just use the white charcoal to define the shape. This works better than the ink I think.
Using ink meant I kept the white perspective lines, but when the structure itself is white, it looks better to rub out the perspective lines which is very easy to do with this white charcoal.
The structure disappears very nicely behind some of the brush-strokes and really creates a sense of depth and height!

The shape of the second experiment also works much better than the first. It mimics a gap in the tree canopy and looks grander – filling more of the space.
Reasons the second structure works better:
-The top of the structure matches a gap in the paint marks in the painting. —Having a corner of the structure facing the viewer closes the shape off to the viewer and decreases the feeling of being under the shape I think.

I’m not sure whether I’ll use the white charcoal to define the shapes more. It works here for a small painting but on a bigger scale I can imagine the thin charcoal lines are far too thin and faint to make an impact. Using tape with a white background may do the trick – keeping this straightness and structural feel whilst creating impact.