I'm assuming you mixed up the Gamvar solvent with the crystals first. Personally, I use glass to mix my mediums and varnishes, not metal. Seems cleaner. After everything is mixed up I shake for one hour all day and let it all sit for a day or two.
When you mix up the slurry you need to introduce the beeswax gradually. Otherwise it may not be properly emulsified. In the final concoction there will always be tiny bits of undissolved wax in the final mix, which I would call more opalescent than opaque. White gesso is opaque.
Definitely test it out on an old unimportant painting that's sufficiently dried (6 mos to 1 yr). If you don't like what you see after it dries (couple of hours), you can always remove the varnish with Gamsol (mineral spirits). Then if you feel it's too mattte, add more Gamvar.
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