Created this triangle of art for evocation, it’s made out of paper, and added layers of the 7 colors of the rainbow with colored paper to symbolize the triangle as a platform for materializing light, metaphysical energy etc, into solidified matter, like a personal rainbow bridge 
however since it is made out of paper, it might be best to place something heat resistant where you place your censer but obviously no necessary if you’re using a black mirror or crystal ball, I personally don’t think a circle is necessary, in my opinion the triangle isn’t necessary either but it is a cool modification especially since it symbolizes the materialization process of the spiritual influences through the descending rays
It’s feels like a universal remote