wrapping vines around coffee mug handles and so on--would a ceramic coffee mug not bake well, or is it the microwaving issue? I read the Covering articles at Glass Attic, but didn't see the answer I was looking for exactly....or if there's some dangerous thing about it so it isn't done.
First, when you ask about "not baking well" or "the microwaving issue," I'm not sure if you're thinking of initially curing the clay, or of reheating a drink in the microwave perhaps repeatedly.
There would be several issues with putting clay onlays around coffee mugs or even on coffee mug handles, but putting onlays onto glass or ceramic then curing them in a regular oven alone wouldn't be the problem. The same potential issues and ideas would be discussed under the Glass and Ceramic
category on my Covering
page where there are glass goblets covered with onlays, as well as all kinds of cups and glasses covered with clay but used then as pencil holders or far enough away from real heat that it wouldn't be a problem (around candle flames or nightlight bulbs for example, or on the back of glass plates or bowls which might contain hot food) --glass is a pretty good insulator too.
The possible problems/dangers would come also from any clay that would be touched by the lips/etc (which we just don't do to be uber-safe), or from making the cup really hot by putting a hot drink into it (if hot enough, there could be a noticeable clay-curing smell, or the clay or any adhesive you used may soften), or perhaps from microwaving the cured clay on the cup, especially repeatedly (which could cause the clay to darken or burn??--don't know about that).
You may also want to check out my page on Onlays
... may be other info or ideas you'd be interested in?http://www.glassattic.com/polymer/onlay.htm
And here is the page on Safety
(there you might want to click on Food & Drink
and/or Fumes & Burning
P.S. One thing about ceramic
materials to keep in mind is that they tend to heat up hotter than the ambient air temp in an oven, so they could more easily heat up enough to darken the clay you use on them (especially because the clay could also be thin). To keep that from happening, you'd probably want to use an enclosed or partly enclosed baking method, or use Kato Polyclay which doesn't darken easily, or to use a lower baking temp and bake for longer. (When baking regular clay items on a ceramic tile, or a metal surface too, the same thing can
happen and the bottom of the item may get darker, so it's a good idea to put some kind of insulation between the ceramic tile and the clay even if it's just a few pieces of paper or a layer of cornstarch.)
Ask again with more specifics if those things don't answer what you were really asking!