A very quick video that demonstrates how to prime a miniature using the ‘Zenithal, or Sketch Method’. This will establish your highlights and shades using different shades of primer.
Alternately, this can also be done with dry brushing grey and white over black primer.
This will allow one to paint thinly over top with very little effort required to establish smooth shade and highlight transitions. Alternately, it can also assist in figuring out your light sourcing.
Army Painter Primer