Glass for beginners

Go at least a quarter inch smaller in diameter than the largest thing you've taken comfortably. Glass is hard, and if you can take 1.5" in diameter of silicone or some soft material, then 1.25" in diameter or less will likely be okay for glass or other hard material.

Of course, make sure that the dildo has a suitable base or a suitable length (at least 8", I think, is the recommended... someone can correct me on this) before putting it in your butt, so that it doesn't slide all the way in you.

While glass is seamless, it is unforgiving, unbending, and unyielding. There's no squish. At all. I suggest that starting with silicone is the way to go. Most silicones have only visible seams (if any seam at all) and won't be felt in use.

I would definitely suggest silicone for anal before using glass. Like Annemarie said, if you do go with glass, get something smaller than you are used to in a soft material. Remember to get something with a wide base when using anal, I wouldn't count on length.

I got a glass plug for my first anal toy, but it was much smaller than the Moon Plug. I got the Pleasure Pearls link It is about the diameter of the average middle finger. With some thrusting (once you're used to it) the little round balls can give a really nice sensation.

I am also looking into glass. Nice post.