Inlay Techniques to Salvage a Split Bowl
I turn mostly green wood. The process I use is to:
Rough out a bowl so that the wall thickness is approximately 10% of the largest diameter
Slow dry the roughed out bowl for at least 6 months
Re-turn the bowl to final shape and symmetry
Sand and finish
Green wood turnings always warp as they dry, and may reveal splits and cracks that were not apparent when the bowl was roughed out. These split bowls can usually be salvaged by inlaying the cracks with colorful minerals or metallic powders.
To do so:
Sand the bowl starting with 100 grit and progressing to 150 grit.
Apply a hardening oil (e.g., tung oil) to the bowl and let dry. Make sure the oil fully soaks into the wood around the split. This may require several applications of oil.
Clean out the split using a rotary tool (e.g., Foredom, Dremel)
Apply a dark dye to the edge of the split, if you wish to accentuate the inlay. Do so with a light hand, and apply it inside the split rather than on the outside of the bowl.
If the crack is deep, pack it with sawdust to within 1/8" of the surface of the bowl, and apply thin CA glue to the sawdust to lock it in place. Wipe off any excess CA glue that gets on the surface of the bowl. The oil applied earlier will prevent the CA glue from seeping into the wood and discoloring the surface.
Place inlay material into the split. You want to have the inlay material mound up very slightly above the surface of the bowl, and extend to cover slightly more than the edges of the split. Carefully flow thin CA glue into the inlay material. Make sure the inlay material is fully wetted out, and carefully wipe off any excess that may have gotten on the surface of the bowl.
After the CA glue sets up, inspect the area to see if there are any pits or hollows in the inlay. If there are, add inlay material to those areas and add a drop of CA glue to lock the inlay material into place.
Once all the splits have been filled, carefully sand down the inlay using 120 grit sandpaper until it is smooth and flush with the surface of the bowl. Try not to oversand and create a groove.
Re-mount the bowl on the lathe and resand, starting with 100 grit and going through your typical progression of grits. I usually stop at 280 grit.
Apply final coats of finish. If you are going to put a lacquer coat on the bowl, you will need to put a barrier coat of shellac on before you spray lacquer. The oil you applied earlier in the process will prevent the lacquer form adhering well unless there is a barrier coat between the oil and the lacquer.