What is it and is it safe?

Like glazed doughnuts? That's usually powdered sugar, water and flavoring like lemon or vanilla. Or, a glaze can be thinned out jelly.

What is it on?

Vitamins

Food glazes are additives that provide a protective coating and/or shiny appearance to foods. Generally they are based on a wax like beeswax or some other crystaline wax. Your best bet is to contact the vitamin manufacturer to determine if the product is safe to consume.

Usually vitamins that are coated don't really break down as well. So they don't absorb into your body very well and you don't get as much benefit from them compared to vitamins that are not coated.

Hmmm, I wonder if this is what irritates my gut.

I am not sure but I think some food glaze has gluten. I had a very definite reaction to some Trader Joe's chocolates and the only ingredient it could have been was the food glaze. I don't react to the non-shiny chocolates. I called their 1-800 number and they said the chocolates did have gluten. There was no other place for it to come from.