An isolation coat is a clear, non-removable coating that serves to physically separate the paint surface from the removable varnish.
The isolation coat protects the painting if/or when the varnish is removed by separating the pigmented area of the painting from the solvents used in removal. It also helps to seal any absorbent areas in order to create an even surface on which to apply the varnish.
Sealing absorbent surfaces of the painting with an isolation coat will assist in the varnish application. This will prevent the varnish from being absorbed within the surface and allow the varnish to function as an easily removable topcoat. This is especially important when using a Satin or Matte varnish because the liquid of the varnish can be absorbed into non-sealed areas leaving the matting solids exposed at the surface and creating a dusty or cloudy appearance.
