RPF PREMIUM MEMBER
Ah. It's in the technique. I actually searched my bathroom quickly and found a spray bottle with "Febreze Air - with GAIN".
I set my idol outside and sprayed a heavy coat of Febreze on the surface, and then while it was still wet, I threw the dirt on it. The dirt stuck to the wet Febreze. I noticed that more stuck than I wanted, so I got an air duster can (canned air) and sprayed off the larger clumps of dirt, which left a thin layer of dirt, as if it had accumulated over time. The dirt is especially visible in the bright light, and at that angle of camera shot. It is actually not as visible under normal conditions. It looks muted, but not decades worth of dirty, accept under those exact conditions. The lighting and angle and close up shot, all combine to get that particular look. They thought that all out in advance, and I simply tried to duplicate what they did.