In the 3rd part of the the lipstick tutorial dealing with modeling, the clear plastic cap is examined for its potential to greatly impact render times. The lathe object is a spline based object and this can be slow to render when a refractive material is used. This tutorial shows how to render it as a polygon based object to get the best render time.
A follow-up tutorial going into some further details regarding Render Splines as Polygons on objects with refractive materials can be found here.
