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Hi Bill, I addressed this issue in the video. Mel the owner of Sheffield explained to me that bronzing powders have to be dissolved in the solvent and made into a syrup before being mixed with the spray medium such as lacquer. Otherwise they stay as particles and will separate.
-chris
"Where TONE is Key, and Mammoths are not extinct."
To add from the sideline perspective of a chemist who has worked some with dispersions and coatings:
To my best knowledge, the technical issue is not "dissolving", but wetting. The metal particles cannot dissolve in organic solvents. And a good thing this is too, because if they would dissolve, they would no longer appear as a metallic lustre, but as a coloured transparent solution, e.g. bluish or greenish (the colour of dissolved copper and its alloys).
So, while they must indeed remain particles (like any metallic finish), the issue is that they must be wetted thoroughly in order to disperse properly and to remain dispersed after spraying. If the two powders have different degrees of wettability, or different affinities for the specific solvent, that might well lead to separation, agglomeration, unevenness, etc.
Wetting can be achieved through choice of solvent, through high-shear mixing, through addition of wetting agents, etc.
Autodidact interested in piano technology. 1922 49" Zimmermann, project piano. 1970 44" Ibach, daily music maker.
Just to clarify, my experience was not any test. Like you, I needed a different color than what I had. I mixed two random powders together and was surprised when they would not mix(I mix stains all the time). Maybe it was because they were two different brands. I don't know. I ended up spraying a red dye over the finish to get the color I was looking for. It actually came out very nice, but I was worried it would be impossible touch up if I ever needed to.
Professional Piano Technician serving the Tampa bay area. website: mckaigpianoservice.com