Planning for wood finishing also involves thinking about the properties of the wood being finished, as these can greatly affect the appearance and performance of finishes, and also the type of finishing system that will give the wood the desired characteristics. For example, woods that show great variation in colour between sapwood and heartwood or within heartwood may require a preliminary staining step to reduce colour variation. Alternatively, the wood can be bleached to remove the natural colour of the wood and then stained to the desired colour. Woods that are coarse textured such as oaks and other ring-porous hardwoods may need to be filled before they are finished to ensure the coating can bridge the pores and resist cracking. The pores in ring-porous woods more readily absorb pigmented stain, and advantage can be taken of this to highlight the wood's grain. Some tropical woods, such as rosewood ("Dalbergia nigra"), cocobolo ("Dalbergia retusa") and African padauk ("Pterocarpus soyauxii"), contain extractives such as quinones, which retard the curing of unsaturated polyester and UV-cured acrylate coatings, and so other finishing systems should be used with these species.