Is it poison for useing a clay pen holder as a mug?

If it works, and doesn't crack and break apart, it should be fine! Only, it may be difficult to wash and dry efficiently, and more delicate in handling in the kitchen sink etc... Using it as a coffee cup will shorten its existence as it is.

there's special glazes for things supposed to be used for food. If they were making pen holders then the teacher wouldn't have used the more expensive food-safe glaze because it was unnecessary. I also doubt that a 4 year old would have completely covered the thing with glaze anyways. Don't drink out of it.

If there's a glaze on the inside it's more than likely safe.

if it is completely selaed, then you can probably drink out of it safely. but if its just the straight clay, then over time the liquid would probably soften the clay and god only knows what that clay is made from. i wouldnt drink from it.

I'd tell dad to use it as a pen holder only -- better safe than sorry!

Hell no you don't know what kind of stuff that 4 year old put into the clay!

eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee