Hatch fills or pixel art plotting requires a rather precise estimate of your particular pen/paper combo’s stroke width.

For example, this test pixel art plot would benefit from a slightly thinner pitch to avoid the visible overlap between neighbouring lines:

plotted obama pixelart with visibly overlap between neighbouring lines

There is no way around experience to find the optimal pitch. I’ve created the fill_test sketch to create custom charts with test patterns precisely tuned to the pen of interest. There is indeed no point to testing a rotring isograph .35mm pen with a generic 0.1mm to 1.0mm chart.

Here is how the UI looks:

UI of a fill test pattern generator sketch made with vsketch

Beyond the general layout options (page size, grid size, etc.), the Smallest Width and Width Increment parameters enable a fine-grained exploration of pitches around the nominal pen size.

Here is an example with a rotring isograph .35mm in my notebook, which has a slight propensity for ink soaking. For this combo, fills with .4mm pitch yield the best results:

example of plotted fill test patterns

To use the sketch, download or clone my sketches repository and execute the sketch using your existing vsketch installation:

$ vsk run path/to/sketchs/fill_test