I am setting up a shop to refinish aluminum wheels. I did a test where I removed the old clear coat on a wheel, machined the finish to bright aluminum, and then clearcoated using a Protech powder. I had a thermocouple on the wheel. The wheel was preheated to 250 before coating. In curing, the wheel was brought to 375 nominal, and held there for 15 minutes. (The wheel temp actually went as high as 390.)
When finished curing, it was obvious that I had put on too much powder. There were ‘waves’ and orange peel. However, what was more disconcerting was the appearance. The wheel looked like nickel or perhaps burnished aluminum, rather than bright aluminum. I thought it was just the coating being too thick, but as I am stripping it, it appears that aluminum itself darkened.
Any idea what went wrong, and how I can prevent it?