I shall go with Damar Varnish with Linseed/Walnut ( Why Walnut? IDK, just wanted to mimic the European Renaissance Artists – lets see what happens) binder and Turpentine as solvent.
The ‘glossiness’ and ability to retain color is not much to my concerns; But just a means to protect the yellowed and dulled layer of paint from dust and scratches.
I do love how a painting painted with Linseed Oils only, darkens and dulls over the decades ( though can be re-lightened in sunlight). It seems to give the painting more grace and ‘importance’ in my opinion.
I have been ignoring the ‘Fat over Lean’ Oil:Pigment ratio rule for some time now, I shall try to correct myself in the very next painting.