My old salt pan keeps scorching matte acetates, while a hot-air unit at 180 C gives me cleaner temple bends and holds pantoscopic tilt without stress whitening — what temp and distance are you using to avoid waving thin fronts? Also seeing different behavior with bio-acetate and crystal frames on cold mornings in the shop.
At 180 C I hold 8–10 cm back and sweep for 6–8 seconds, then finish closer only at the hinge — stops ‘waving’ thin fronts; for matte or bio-acetate I drop to 165–170 and pre-warm in a towel warmer on cold mornings. Crystal shocks easier, so heat from the inside face and use a cardstock shield. That combo keeps pantoscopic tweaks clean without stress whitening.
Agree with @dkingston58; angle about 30° and support thin fronts with cork; 2‑minute 40°C towel pre‑warm helps bio-acetate.
I’ve had better luck targeting surface temp: at 175°C with a 20 mm diffuser 12–14 cm away, I pulse 1–2 s from the inside while a 1 mm silicone sheet shields the face, stopping when the shield reads about 60°C — no ripples and matte stays matte. On cold mornings I stage frames on a 30°C heat mat for 5 minutes; @dkingston58, are you using a reducer or wide nozzle? Think marshmallows — pulse, don’t torch.
I stick 2 mil Kapton on the outer surface and clip a small aluminum heat sink on the bridge; at 172°C I work 9–10 cm back with a slow figure‑8 sweep, then a 1–2 s burst closer only at the hinge — keeps matte from glazing and stops the front from rippling. @dkingston58 your cork trick pairs well with the heat sink when pushing panto. On clear I drop 3–5°C.
On thin fronts, I stop the waving by bracing a soft leather pad along the brow while I pulse 170–172°C from the lens side about 7–8 inches out — @dkingston58 do you tweak fan speed or keep it fixed with that 30°?
On ‘cold mornings’, I prewarm 5–7 min at 45°C, then 180°C from 12 cm; cuts waving. @dkingston58 pre‑temp bio‑acetate?
I get steadier fronts using a wide diffuser; 165–168°C for “bio‑acetate” at about 14 cm, crystal nearer 175°C.
Try angling the nozzle about 15° and pulsing 168–170°C from 16–18 cm while rotating the frame; I brace the brow with a silicone pad to keep fronts flat. I start plant‑based acetates lower (165°C) and finish with a brief 172°C pass, while crystal takes a steady 175°C — think toasting, not broiling. @julian_moore92 what nozzle width are you on, and have you tried a paper card baffle to tame bridge “waving”?