These are compositions of various materials and objects made to be seen by transmitted light (perhaps suspended in a window). As such, they were mainly photographed on a light box, or occasionally against a white background, or even a black background, to show how their appearance changes. They are mostly monochromatic, being made with a resin tinted a pale gray, or untinted. (One, tinted a bright azure, pops out amidst all the gray.)
I've used a variety of molds, made out of small cardboard boxes or trays, plastic, or a mixture of silicone and flower. Usually the surface and the perimeter of the mold are coated with a thin layer of clear silicone so that the resin piece will detach itself easily when done. An initial layer of resin is applied and allowed to harden. Then another layer is poured in, and the pieces are arranged in the wet resin. (This arrangement is carefully worked out in advance, as working with wet resin is no time for those decisions.) This layer may include colorant to make the form of the objects within stand out. When that has also hardened, another layer or two may be applied tp completely cover the materials inside.
if the piece is to be hung in a window, I drill two little holes at the upper corners and string a wire from one to the other.