Here is how to perform that surgery using the (no, not the potato). Step 1: The Autopsy Remove the vinyl sash from the frame. Look at the spacer (the silver or black strip between the two panes of glass). If it’s bent or corroded, stop—you need a new IGU (Insulated Glass Unit). If it’s intact, proceed.

If you live in a humid climate (Florida, Louisiana), don't bother. The fog will return in six months. Just buy a new sash. But for the rest of you? Grab the drill. Let’s get weird.

You have a “failed seal.” That fog isn't a ghost; it’s humidity. The desiccant inside the spacer is full, and argon gas has escaped. You have three options: Live with the blur (maddening), replace the whole window (expensive), or perform surgery (cheap & satisfying).