As others noted, they're polished aluminum, which takes care to keep looking nice. If you've allowed sweat or sports drinks to etch the aluminum, you (or someone else) can bring most of the shine back by using emory compound and a bench grinder with a polishing wheel followed by polishing compound. They heat up during polishing so heavy leather gloves are required. You'll want to remove the timing / chain rings for the greatest flexibility in working the arms against the polishing wheel. Hit them with something like Mother's Aluminum wheel polish as a 2nd to last step and them a good wax.

After they've been returned to their nearly original luster -- excusing any pitting that the original acids left on the aluminum caused -- a 10 second wipe down after each ride with a rag, even a few hours after the ride, will prevent any more pitting. About once a month, or whenever you want to buff them up, hit them with some Mother's (it will turn your applicator cloth black) and then buff with a clean corner of your polishing cloth.

Our oldest daVinci cranks are 13 years old and have been knackered by chain drops, Debbie's habit of riding with her heels-in, etc. However, they polish-up in a few moments with Mother's every time and look amazing unless you get up close to inspect. Even then, they still look pretty good for 13-year old cranks with 30k+ miles of use. The ones on our Ventana look a little worse for wear, as I only wipe/wash them down and don't polish them. No acid etching, just not a brilliant finish.

It took me about 2 hours to bring back a pair of daVinci cranks for some friends where the captain was a toxic-avenger when it came to sweat. They were awful when I started and looked really good afterwards with just a few really heavily acid etched spots. Sadly, the didn't heed the care instructions and they eventually corroded beyond serviceability where all of the threads for the bolts, self-extractors, etc. were ruined. They're running carbon cranks these days, which is probably a better choice since they take a little less care. However, the aluminum parts will still corrode if they're not cleaned of sweat, etc.

Could be, but they're hardly out of line with other high-end carbon cranks made in
Asia that are just now becoming a bit lighter than the daVinci cranks, which is pretty amazing considering the daVinci cranks aren't all that different today than they were when we bought our first set in '98.

This is true.

White Industries used to market their own tandem cranks back in the 90's as well. However, they sunset that product line as daVinci improved on their original design for daVinci's house-branded cranks. Early-on White Ind. also made the Ti-grey anodized drive-side chain rings that matched the CNC'd timing rings, and they were beautiful. However, White Ind. backed out of that product line around 2000 and FSA or Specialites TA chainrings have been the fall back for us. I believe daVinci is also spec'ing FSA rings with their cranks.