In 2016 I started to paint these simple looking paintings. They were the result of a two year long search for a way to combine crayon drawing with painting. The resulting method has many specifics and to give you some insight I will broadly outline those in this text.
I will assume a suited surface is already present. Because we will be dealing with both the pressure of the crayon, as well as the absorption of water soluble paint, the expected supports of canvas or paper are unsuited for our needs.
A wooden panel works well. After sanding it is primed, sanded and cleaned to a smooth surface in a normal fashion and then covered with several layers of gesso to create an even, white and somewhat rough surface. If the surface is too smooth the crayon will not stick, if it is too rough it will be difficult to get an even coat of paint.
The painting process really begins with a crayon line.
The crayon itself must not be too soft, for it will completely be absorbed by the paint layers, nor too hard, for it will resist all application of paint. Conté bars are the only material I have thus far found that is suitable.
Then the drawing of the line. Again, it can not be pushed too hard, for the line becomes smudgy and inelegant, nor too soft, for risk of disappearing completely once the paint comes into play.
Over long lines the consistency of the lines breadth is likewise a problem, as the crayon degenerates from a sharp point into its original square form, requiring constant turning of the crayon to maintain a straight line of a constant width.
Next is the application of paint. The most effective is an acrylic dispersion, presumably with a long, cross-linked molecular structure. It cannot be too strong, however, for it will literally break up the crayon line. So it is first mixed with roughly 25 percent water and then a bit of washing up liquid is added, to overcome the natural resistance of the crayon and ensure it is coated by the paint.
After it is mixed, the actual application of the paint still requires quite a bit of care. The brush is one that is straight, long and as flat as possible. The only perceivable store-bought solutions are high-end watercolour brushes, if their width to length ratio permits. The brush should also be damp, but not wet, before being dipped into the paint mixture, repeatedly adding and taking away paint in order to get a homogeneous spread over the entire brush.
You hold the brush perpendicular to the painting and move it down slowly till its tip barely touches the painting's surface. Then push it down an slightly forward, curving the bristles, and move the brush slowly and evenly along the line, still holding the handle perpendicular to the surface. This is very important as you want to have a brush saturated with paint mixture, yet at the same time this mixture should be distributed evenly along the line segment. Holding the brush under a normal angle of thirty to fifty degrees will cause the paint to spread unevenly, with large amounts being deposited in the beginning and little left at the end.
If done correctly, it's possible to cover about ten to twenty centimeters of crayon line per brushstroke.
Both the downward and the forward movement of the brush need to generate the bare minimum amount of friction necessary, so the handle of the brush needs moved with the arm and only be balanced with the fingers.
After a line is traced it is checked for coverage, often requiring a second, third or fourth layer. This can be done while the paint is still wet or done in several stages with the paint allowed to dry in between layers. Longer lines usually require the line to be segmented and painted over in two or more sections.
After every stroke that is made the brush is cleaned, rinsed and dried till it is damp, before the process can be repeated. Painting a single line can thus take up to fifteen minutes and finishing the final stage of a painting often demands a full day of work or more.