Let's start with stupidity. black mirror and scrying through the mirror. The techique is Poke Runyon's in that you're supposed to see the entity in the mirror through you're own distorted face. My vision has never been that good. I did get a perfect pentagram once and some maybes in the mirror.
I then developed a plan to have all the sigils I needed on paper and hole punching the junction points. This would allow me to mark the junction points on the mirror quite easily. From there, all I had to do was connect the dots.
I made a few of them before I realized I was making sigils of their names using the rose cross. Problem? I was doing planetary spirits whose sigils are derived from Kameas! This is equivalent to mispelling an entities name. This is a serious error for a magician. Serious fricken error. Fortunately, I didn't call up anything using this flawed method.