Sorry I said pinned m & t, but what I meant was more specifically a drawbore m & t which is a type of pinned tenon. The pin is slightly tapered and offset from the hole drilled in the tenon and will actually pull the tenon tightly into the mortise. Think of it as a more visually streamlined tusk tenon (which is also pretty common in this style). They are a very easy way to make a nice tight joint without needing extreme accuracy or glue.
Don’t know what your living situation is, but if you think the legs or stretchers on your furniture are likely to get damaged at some point and need replacement or you want the option of partial disassembly, strategically used drawbore or tusked unglued joints can make these tasks much simpler.
That is just the aluminum oxidizing. Essentially rust for aluminum. It will happen no mater what with aluminum cookware unless it is anodized or coated in something. Even then it will still happen eventually. To be fair, the dishwasher is going to affect the appearance of even the most expensive pots and pans over time. It’s one of those things where you either accept it or put in the work (and waste the water) to keep it looking nice. The solution for me was buying stainless steel, throwing it in the dishwasher most of the time then hitting it with barkeeper’s friend every once in a while.