The difference a varnish can make... (or a case for resaturation)

Aside from becoming yellowed and dark, a varnish can also become desaturated, imparting a very matte and generally obscured painted surface.  In many cases, where the original varnish cannot be removed, the varnish can be resaturated with the addition of a fresh coat.   This portrait of a Native American by Dunlap, 1914, is one such example.   The surface was obscured by a heavy layer of dirt and the varnish was uneven and matte. 

The new layer of varnish restored clarity and depth to the image without requiring old layers to be removed.  Other treatment steps undertaken include humidifying and flattening planar distortions, removing two lodged keys in the lower right corner, retouching wide aperture cracks, and mending a compound tear in the upper right corner.