Natural spalting is best, no way around it.

But years ago when I was doing a lot of wood turning a lot of us were "force" spalting by rough turning a bowl, Christmas ornament, or just about anything else, and we put the objects into a tightly sealed trash bag covered with all the green shavings.

Left it under my storage room for several months, and the molds and fungi would do their work. Got some interesting stuff! For anyone that tries it, soft woods work best. Take the molded stuff out of the trash bag and let it dry out slowly over a month or so then turn it.

Robert