You can use any type of clasp that you prefer.
However, pearl knotted jewelry is very strongly associated with what are called pearl clasps or safety clasps. These are often marquis-shaped clasps, with a hook like tongue that pushes inside them. If the tongue should somehow come undone and slip out, it would catch on a bar in the clasp, saving you from losing your string of pearls.
In terms of that vintage-type look, other widely used clasps are filigree or other box clasps. These are pretty, but not as secure as safety clasps.
Usually, you will want your clasp to compliment and not compete visually with your pearl knotted piece. If you decide to use a very show’y clasp, it should blend organically with the rest of your piece.
You will be attaching your bead cord, either to the loop(s) on the clasp itself, or to soldered rings attached to these loops. You want both these loops, as well as any rings attached to them, to be closed, that is soldered — thus have no gaps in them. If there are attached rings, and they are open, you will want to remove these, and attach the cord to the closed loops on the clasp.
Whatever Your Preference,
You Would Be Hard Pressed Not To Use A Pearl Clasp
If you are making pearl knotted pieces for re-sale, you would be hard pressed Not to use a pearl or safety clasp, or some similar looking clasp.
The woman who originally owned the American Pearl Company in Tennessee was always looking for a clasp that would be durable, but attractive to her customers. The American Pearl Company made a lot of its money by selling finished jewelry.
Pearl and Safety clasps, particularly those made of 14KT gold, break easily. The tongue bends and breaks, and no longer can wedge into its…