I wash all my glasses, including Riedel Sommeliers, in an old GE dishwasher with only a sprinkling of something called Finish, which used to be called Glass Magic (it now says “Finish Glass Magic” on the box). Available from Amazon and some stores.
Some of my glasses I’ve had for 25 years, and there’s no discoloration. Over time they get scratched somewhat, mostly from bumping into each other when carried by hand or on a tray. That’s pretty much impossible to avoid, but you can minimize the scratching by taking care that the sides of the glasses don’t come in contact with each other.
I find decanters to be more difficult, and have pursued many of the same techniques already described. Sometimes they get an etched pattern that I’ve been unable to remove.
It also depends on the water where you live. We have a half-a-house in Santa Barbara, where the water is so hard it has to be heavily softened, and I can’t use the dishwasher there. Glasses get cloudy fairly quickly, so I wash them all by hand, rinsing with RO water. That seems to work, but takes a lot longer!
In a similar vein, although cheaper, coarse ground salt or crushed ice scrape out a lot of gunk from decanters. Might not work for cooked on stuff as seen in the coffee pot, though.
Over time they take on a purple hue that I’m convinced is not a stain but wine that has absorbed into the glass.
Depends on what you mean by “absorb”.
Glass seem incredibly smooth to us but down at the microscopic level it is actually a rougher surface than it seems. There are tiny little hills and valleys and little bits and pieces of various things can get stuck in those. Over time, you get enough of those and the color in your wine, tea, coffee, tomatoes, and other things can end up coloring the glass. But it’s only surface color and all of those are organic compounds that come out with a little vigorous washing, which is what the brushes, beads, BBs, and beans help accomplish. And it’s why bleach works.
In other words, the color doesn’t get “into” the glass. It clings only at the superficial level and it’s easily removed.
Fill the decanter with hot water, drop 2 Polident tablets in and let stand overnight…next day, pour out Polident solution, rinse with clean hot water and brush, if necessary…works everytime…