I use an old electric coffee grinder,throw in small stones and pulse until ground to your liking. Then its just a simple matter of cleaning out loose material from knot hole and put a bit of super glue in the hole and sprinkle with rock dust let dry and repeat until turquoise is above wood level,I then use a file to take the stone down to almost flush with wood and then sand the whole surface as if the stone wasnt there. I'm sure there are other ways, this is the way I learned from a wood turner who makes amazing bowls and such. Hope it helps
