I can't answer that in the absolute, and I suspect that it is a question that will remain unanswered for many years to come. But sometimes it is possible to pinpoint the germ of an idea, and even to track its development.
My recent (and ongoing) series of colourful trees is a nice example.
The original inspiration was the sight of exposed tree roots on the top of an Avebury rampart. I was in company and didn't have time to sketch such an intricate subject, so I took a photograph.
That one photograph was the source for several sketches, in various media:
Media, left to right:
Acrylic ink, Line and wash, Acrylic paint markers
... and one small painting on canvas (which will be for sale on the Princes Trust stand at the Reading Contemporary Art Fair):
The colours in the negative spaces were quite exciting and led to further developments of the idea.
|Acrylic, applied with a brush.
Highly stylised approach emphasising colour
|Acrylic (brush) and acrylic paint markers
More naturalistic, and pleasingly delicate, while retaining the colour variation within the negative spaces
|Acrylic applied with a knife (over brushwork)
Stylised and angular
Acrylic's quick-dry nature also allowed me to flatten the colours in a nicely "Modern" way. The paint marker pens allowed me to indulge in linearity and add twiggy detail; they also permitted me extra working flexibility.The knife, on the other hand, allowed me to reject the detail and precision of the pens and to maximise the glowing potential of neat acrylic colour.
Each of these final approaches has their merits. It depends on the effect I am trying to put across and the nature of the subject (trees have characters, and the composition will also inform the approach).