Many of my customers send me gemstone beads to be knotted.Generally these are always a problem!
Why? Well mostly the hole size is either far to small for the weight of the necklace or in a necklace with a mix of beads there are different size holes.If the hole size is very small then the thread will have to be thin and knots will slip into the bead holes.
So if you are buying beads and they are stone or heavy glass ones and you want to knot them check the hole size is between 1 and 2 mm or even 3 mm for very heavy beads.
And if you do have a necklace of mixed stones some with very small holes do not try to knot them but use a multi - strand softflex thread (49 strands is best)
I did not create the necklace below but am including a picture to show a necklace with lots of different types of beads which is knotted. Lucky for the creator the knots look nice and strong so they managed to use a good thick thread!