Which of the following preservatives is categorized as permanent?

In the context of preservation methods, the classification of preservatives as "permanent" typically refers to their ability to provide long-lasting protection and stability over a significant period of time without degrading or losing their effectiveness.

Paint is often considered a permanent preservative because it creates a durable barrier on surfaces that protects materials from damage due to environmental factors such as moisture, UV light, and oxidation. Once applied, paint can adhere firmly and withstand external stresses over time, thus providing ongoing preservation.

In contrast, other options like oil, wax, and grease, while they do provide protection and have their own merits, may not be classified as permanent. These substances typically require reapplication or maintenance to maintain their protective qualities, as they can deteriorate or wear off due to environmental exposure or physical contact. Therefore, paint stands out as the correct choice for a permanent preservative due to its lasting protective qualities once cured on a surface.