I mentioned recent fun with metal a couple of days ago; I was not entirely thrilled with the finish that the aluminum parts had. I had sanded starting with #80 sandpaper, then #220, #320, #400, #1500, finally #3000. While this began to give the aluminum something of a mirror finish, it was still not a genuine mirror finish. So I used a product called Mr. Metal Polish, and it certainly got me close to what I wanted.
It is certainly good enough for what I'm shipping the customer, but I found myself wondering how much work would be required to achieve a true mirror finish. So I went to Harbor Freight today and bought a buffer. The results were quite interesting. I started with a piece of aluminum scrap that had not been sanded at all, I was surprised to see that the buffer, in conjunction with Mr. Metal Polish produced a pretty impressive reflective surface. On the other hand, a piece of scrap that it been sanded on the lathe to at least #400 did not improve at all.
My next step, based on previous experiments a year or two ago, was to pull out some Mother's Mag Polish and try that. The unsanded scrap now achieved a really impressive mirror finish, once I had washed it and wiped it with a paper towel. The scrap that a been sanded on the lathe did not improve at all. I then sanded the scrap with #1500 sandpaper, and buffed it again with Mother's Mag Polish. Now it was a pretty respectable mirror finish, although no better than the unsanded scrap, and perhaps even a little worse; it was hard to tell.
My guess is that the unsanded aluminum, while it is a unattractive and dull finish, is actually pretty smooth, and buffing with the Mother's Mag Polish takes it to a very nice shine. By comparison, even the scrap sanded with #1500 sandpaper is probably much rougher of a surface then the mill surface of aluminum. This suggests that it is a waste of time to sand aluminum to make it shiny (which it does certainly do), and it makes more sense to invest less time into buffing the mill surface with Mother's Mag Polish.
Amazingly enough, the current container of Mother's Mag Polish appears to be one that I bought in the late 1970s when I first owned a car with mag wheels. And yes, this says something about how much I care about beautifully polished mag wheels on my cars. Or perhaps it says something about how long a jar of Mother's Mag Polish lasts.