Quick trivia: on float glass, the tin side will fluoresce under a 365 nm UV flashlight due to residual Sn — do you ever check it in the field before IGU assembly? I’m curious if confirming tin-out on low-E lites has reduced your edge-seal callbacks; we saw a 0.8% improvement last quarter when the line started enforcing it.
I carry a $20 365 nm penlight and mark tin‑out with a grease pencil before IGU build; PIB smear from tin‑in on soft coats drives me nuts, and doing this cut our sealant touch‑ups a hair too (not as much as your “0.8%”, but noticeable). Caveat: on dark tints/laminates the fluorescence is weak, so I keep a cheap tin‑side detector as backup and only trust the lamp in a dim corner. Are you checking both lites or just the coated one?
I mark “tin-out” at receipt with a tiny paint‑pen dot on the spacer side and mirror it on the cut sheet so assembly doesn’t have to guess. Caveat: lots of penlights are really 395 nm; true 365 nm shows a sharper bloom, and on tempered/laminated low‑E I’ll double-check with a tin detector wand if the UV’s muddy. Have you seen more misses on laminated lately?
I’ve found using a UV flashlight really helps identify the tin side quickly, especially since you mentioned it fluorescing under 365 nm. It might be worth double-checking the flashlight specs, though — some go up to 395, and I’ve had issues with those not being effective. Have you noticed any difference in callback rates since enforcing this procedure?