Woods rich in resin such as pine, Swiss pine, etc. must have the resin removed before staining or coating. This can be achieved in two ways:
By saponification: to do this a lye is applied to the wood that saponifies the resin, making it water soluble. Subsequent washing and neutralising is often required.
Dissolving the resin with a solvent, e.g. acetone or a cellulose thinner. The resin sludge needs to be removed immediately with absorbent cloths or sawdust