A resin is a solid or highly viscous substance made from plants or synthetic materials that is usually able to be converted into polymers. Resins are typically organic compound blends. This article focuses on resins that grow naturally. Resins are made from sap that generates "wounds" on trees. It is commonly used in commercial harvesting to score the bark of resin-producing trees to allow the drops or "tears" to generate and collect once dried. Ancient cultures may have made the connection between the fragrant nature of some types of burning wood and the sap in those trees. It was not long after that that the decision was made to harvest this material from living trees. Resins are best effective when placed on burning charcoal.