Proudly American
Read the film alongside the fuel history
Regency explains that moisture in fuel and firing conditions can contribute to dark glass, and that some units can show darkening during lower burns. Note the wood source, whether moisture was measured on a freshly split face, how far into the burn the film became visible and whether the pattern changed after a new load. Dark glass alone does not tell you how much deposit is in the flue.
Record shape without diagnosing the stove
Draw a quick outline of the cold pane and shade the area where film returns first. If one corner consistently blackens, mention that along with any change in the latch, visible door seal or appliance controls. One-sided film is an observation; it does not identify a failed gasket by itself. A model manual can tell the provider how that appliance directs air across the glass.
Clean only within the appliance instructions
Identify the glass material and any special coating before choosing a cleaner. Work only on a completely cool, intact pane as directed by its maker. Avoid scraping or using a household oven product simply because it removed grease elsewhere. If a crack, loose pane, damaged seal, or smoke entering the home is also present, put off further use and arrange an assessment. Cleaning makes viewing possible; it does not repair those conditions.