Which of the following is classified as a natural resin?

Copal is classified as a natural resin because it is a tree-derived material that has been used for centuries in various applications, including varnishes, incense, and traditional art mediums. Natural resins like copal are produced from the sap of specific tree species and harden over time, gaining a unique aesthetic quality that enhances the materials they are combined with. This characteristic makes copal distinct from synthetic options, which are chemically engineered substances.

In contrast, polyurethane, epoxy, and acrylic are all synthetic resins created through industrial processes. These modern resins are designed for specific performance characteristics, such as durability and resistance to weathering, but they do not originate from natural plant sources. This distinction is essential in understanding the differences between natural and synthetic resins in the context of painting and coating applications.