I was using “varnish” as an analogy. There are products at the home
improvement centres for field stones which promise to do everything
paints and stains do for wood. Some are clear finishes, flat or
glossy. If nobody here has experience with them I may do more trial
and error.
I did try a product called “Aqua Mix” on granite. It soaked in and
left a flat finish which hardly changed the surface appearance at
all. But I wonder if I wasted my money because it soaked in like a
sponge.
PtP