How to Varnish a Painting in Oil, Water-Mixable Oil or Acrylic - Jackson's Art Blog
For oil painters: Increase the fluidity of your paint by mixing the colour with glaze medium (a mix of linseed oil, dammar varnish and solvent), and apply with a fine round or rigger brush for flowing, even, unbroken lines.
Lisa Takahashi • Ways to Sign Your Paintings
No matter what painting technique is employed, oil paints are most cooperative when applied from dark to light, wet-into-wet.