I'm using Spectrum 96 glass, two layers or 1/4" plus small detail in an overall 14" diameter round. I understand to avoid bubbles, it helps to do a "ramp freeze" so I went 60 dpr to 1300 then 4000 dph to 1480, then 1200 dph to 1000, 300 to 955555 and finally 200 to 800 and off. I STILL had one large
bubble that opened.