The cut is evened out along the surface so as to leave it ready for sanding.
Advanced Woodturning Project
Black Cherry Vase - Page 4
Using an interior light as a thickness gauge for the vessel walls
While the light shows well with just the natural wood...
it can be enhanced with a finish, here a thinned varnish, being applied to the inside of the vessel. The wood is so thin that the finish quickly bleeds through and is seen on the outside of the thin section.
The finish is wiped as dry as possible and the light is reinserted, being careful to keep it away from the wet surface.
The cut is continued and the wood thinned...
until the light is constant. Remember that lines in the natural coloration of the wood may appear as thick wood but is just a dark line.