Look at the trunion. Is this possible?
The rationale behind why I say this is an oil painting is twofold: The impossible effects of light as depicted on the surface of solid objects in the picture and the distorted or incorrect use of foreshortning.
I too have a passion for fine art, I may not be a modern day Rembrant like you are RC, but I am an avid amateur.
How could a light source cause that brilliant white neon bar on the chase of the barrel and then end so abruptly at the ring of the second reinforce?
There is a direct light source coming from above the rear area of the barrel, this is traceable from the shadow cast on the ground by the cascabel. Why does the distinct shadow of the pommelion of the cascabel cast on the ground seem to also show the shadow of the neck of the cascabel leading forward and narrowing to an eventual perspective point? How could this possibly be in the real world, where is the large black area that would be cast by the massive breech area of the barrel? I can tell there is a strong light source coming from the right of the picture by the harsh pool of reflected light on the stone floor, so how come the outside surface of the right cheek isn't brightly highlighted, and how could three-quarters of the rear area of the barrel be in darkness when that apparition (for lack of a better descriptive term) that is resting on the top edge of the bracket is so brilliantly lit?
Errors in foreshortning: As and7barton has already noted, the right trunnion seems to be floating; if you trace the foreshortened circle of the right trunnion face you can see that the bottom edge of the trunnion wouldn't actually be seated in the pocket of the trunnion cut out. Following the bottom outline of the barrel from the muzzle to the breech leads me to believe the barrel is mounted crookedly in the carriage; why is there such a wide gap between the barrel and the inside top edge of the right cheek?
There's also the practical matter of that thin board resting on the last step of the carriage supporting the entire weight of the breech, but then again maybe it isn't, maybe that white hand is attached to the ghostly figure of Francisco Goya and he's under the gun supporting it with his ectoplasmic backside.
I now see that two posts have been made while I've been wasting my time on this; damn you Richard!
Edited 10:51 AM