Glass shelves in a carved case are not simply dropped in. They have to be carried, and how they are carried decides whether the piece looks light or looks propped.
The obvious method is a metal stud at each corner, which is quick and always visible - four bright points that catch the eye every time you look at the shelf. So our artisans do it differently: a shallow groove is worked into the timber at each side of the bay and the glass is slid into it, so the shelf is held along its whole edge and the fixing disappears into the carcass.
That also solves the strength problem. Glass supported at four points has all its stress concentrated at those points and will fail from a corner; glass supported along two full edges spreads the load and carries far more weight for the same thickness. Which in turn means the shelf can be thinner, and a thinner shelf is what makes an open unit look like air rather than like a stack of slabs.
The groove is cut before the interior is finished, and the glass is fitted last - so the shelf can always be lifted out and replaced without disturbing the carving.