early electric vintage brass factory light, industrial ceiling fixture w/ original glass shade

Early electric brass ceiling light fixture with ususual steel slip shade mounting, and the original pressed glass bullseye fresnel rings shade. Measures 7 1/2" deep overall with the shade in place, and holds a shade with a 4" fitter. We didn't see a maker's mark on the shade or the fixture.

The glass shade has no chips or cracks, but quite a bit of mottled brown discoloration from age, heat or soil? We couldn't clean it up with a mild dishwashing liquid, but we haven't tried anything stronger!