Vapor smoothing is a post-processing method used in 3D printing to create a shiny surface finish on a part. To use vapor smoothing, warm up acetone on a heated surface. Place parts in a container above the burner where the vapor will rise up and partially melt the parts to create a fine surface finish. You can also buy commercial vapor smoothing stations. Please note that acetone is slightly toxic and the area should be well ventilated. However vapor smoothing can diminish the strength of the part. It may be best to polish parts with a rag dipped in acetone.