I’m coating some 17″ aluminum wheels with mirror red. The oven door doesn’t close all the way because the wheel is too big. I cover the opening with foil and set the temp to 450 instead of 400. I have a few flakes of black ash like deposits here and there. Is this due to the higher heat? Also the wheel is close to the elements due to its’ size and the inside which was on the bottom got a little burnt. Can anyone help me with this. I’ve done smaller jobs with good results but mostly I am new to this. Thanks in advance.