Losket marks your craft with the flights it has been through. Re-entry scorches the surfaces that took the heat, and engines and rotors coat the hull in dust the colour of whatever you landed on. Both accumulate over a vessel's lifetime and are saved with it.

Losket adds a toolbar button in the space centre, the editor and in flight. It opens a small window with the global defaults. The same options also live in Settings > Difficulty > Losket.
Everything else is per part, in the editor. Right-click a part and look for the Losket group:
In flight the same group reports how much scorching and dust the part has accumulated, as a percentage.
Defaults apply to newly placed parts only. Changing them does not touch parts that are already on the craft.
English, French and Simplified Chinese. Adding a language means duplicating a
block in GameData/Losket/Localization/losket.cfg and translating it.
Raw stats are from the beginning of time until now. Each follower and download entry represents one hour of data. Uneventful hours are omitted.