You can try "sanding" the wood with the back side of sandpaper or extremely fine micro-mesh. This will seal the top layer of the wood and make it very smooth and shiny. I'm not sure how well it will work, I've never tried this for the chins, but it is a common procedure I use when making clarinet reeds. Although reeds are made out of cane which is a lot more porous then pine or other woods, so again I'm not sure if the results will be the same.