What causes butter to make risotto shiny? Why does the addition of butter make risotto shiny?  Is there a chemical explanation?  I was taught to initially saute onions and garlic in olive oil, then risotto Arborio rice with warmed broth until the dish is almost complete, when the rice is still quite al dente.  At this point, I add butter, which invariably makes the risotto beautifully shiny.  Without the addition of the butter, the risotto does not develop this sheen.  I would like to know if anyone knows why?  I am also interested in knowing if there is a specific chemical reaction associated with this process?
There is no special chemical reaction. Melted fats are glossy, look at any oil in a bottle. 

When you add the butter, it coats the rice, and this coat of fat is glossy. That's all there is to it. 

I don't know the exact explanation of why all oils are glossy, but it probably involves quantum physics. You could ask it on Physics or Chemistry SE, it is beyond our scope here.