On my next to last batch of bowls roughed out, there were 12 cracked ones for reasons unknown. As an experiment, I soaked each one in a
50:50 mixture of white glue and water. I soaked each one in a plastic tub, with a brick on it to keep it submerged, for 2 days. Then I put two strips of wood across the container and turned the bowl down on them to drain for a few hours, wiped the remainder off and set it back to dry.
Most of the cracks were initially about 1/16 inch wide some were 1/8 or a little larger. One showed no improvement. One was completely healed. Even after completely drying, finish turning and sanding I never found the original crack. Most of the others when finished have what looks like a black hair where the crack was. This decreases their value but tells me the procedure is not totally worthless.
I probably will not use this again but it is an option for a irreplaceable piece that cracked. Note: All these bowls were Sweetgum.