I use the mirror method too, very fast and easy to use. One thing I found when I made the hole in the mirror is the aluminizing wouldn't scrape completely clear. I tried putting some acetic acid on it to etch it off but to no avail. Then I tried mixing a little sodium sulfite into the acid, creating some sulfurous acid I think. Cleaned up perfectly clear. A drop of battery acid or hydrochloric (mix salt and acetic) should do as well. Wash well and keep the stuff off your body.