I was out for strings and I stumbled upon a slide on display which the store guy said was a hot item. Initially I was like ok yeah but despite my past experience with unplanned purchases I got it and played around with it a little. Here's what the porcelain slide looks like:
It's worn on the pinky. I would categorize it under bottlenecks, it feels more like a glass slide than a metal one, however, not quite the same. At first it felt a little awkward, a little heavier, a little rougher, but like with most things after some getting used to it's starting to deliver.
Here's what it sounds like on my Strat wearing a set of .11 Ernie Balls. Tuning is open E capoed at the 5th fret (key is A).