This guide will tell you how we (It's a Burl) work with the cracks, voids and inclusions found in burl and highly figured wood. 

When I first started I would either trim off or fill any cracks and voids. I ended up with a much smaller piece that did not look as good as when I started. It didn't take me long to figure out that I was going about things the wrong way.

Most burls will have cracks, voids and inclusions. That is a normal characteristic and if dealt with correctly can enhance the unique beauty of the piece.  Don't look at them as a flaw, but see them as part of what makes that piece unique. Instead of trying to hide them, enhance them.

A lot of the time when a burl slab is cut cross grain, it will develop radial checking. Cracks spreading from the center outward toward the edges. We like to draw attention to these. If you take a propane torch and burn into the cracks lightly it will widen the crack a little, get rid of any loose fiber and make it dark inside.  After burning take a stiff scrub brush and brush out any loose charred material.  Then sand the face of the slab as you would normally. When you apply a finish it gives the slab a rustic antiqued look. You can do the same thing on rough outer edges too.

Most burl will form scattered bark pockets or inclusions. Some larger voids. If the bark pockets are intact you can strengthen them with a little CA glue (or crazy glue). If you pack in some sanding dust or finely crumbled bark and then saturate with CA glue you can make that area finish flat and smooth after sanding. Some people like to use crushed turquoise. Depending on the size of the void you want to fill, crush the stone till it is almost powder. Larger voids will allow larger pieces. Pack the dust and pieces into the void and saturate with CA glue. It is better to have it filled to just above the surface of the wood. After it dries, sand and finish as you normally would. Don't be surprised if after you try this once, you start looking for pieces of wood with interesting voids. Plus you can experiment with different materials like other stone, crushed shell, contrasting color sanding dust or who knows what.
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