This is a view of the sides of four stacked paintings, revealing the rounded edge and finished hardwood sides, typically of fine tropicals such as bubinga (curly rosewood), purpleheart (the color of grapejuice), ebony, bloodwood, jatoba, goncalgo alves, paduak, zebrawood, and lacewood, as well as domestics such as birds-eye and curly maple, cherry, mahogany, walnut, ash, and beech.
The painted surface of 3/8" furniture-grade birch plywood is first primed with red-tinted gesso, then lightly sealed with oil to keep it from starving the paint, as well as provide a smooth feel against the brush. The sides are finished with paste wax and danish oil, and may be refreshed with a bit of lemon oil from time time to time. A cleat is glued to the back for easy and secure hanging. The corners are bonded with an internal spline or a metal corner bracket. All works signed on the rear.
below shows details of some older ones, with contrasting corner splines.
I don't usually do that anymore but it could be available on commissions.
if no wood is specified for the sides, then construction is 3/4" birch plywood,
with a dovetail groove routed into the back so it can hang flush on the wall.