Yup! Silk is harder to work with in my experience. Serafil is a breeze by comparison. I also use an awl also to guide the knot to the place I want it, then pull the two threads apart to tighten them. I actually do 5 or 6 small tugs in a row to tighten the knot rather than one hard tug.
If you have a jeweler's loupe (a 10x magnifier), look at the surface of your pearls. Real pearls are very smooth looking while imitation look a bit more rough at that magnification.
See this photo of Renee Newman's: the fake pearls are on top:
Another thing is blemishes. Real pearl strands...
See, this gives me pause.
Real pearls in a necklace are never all the same size. The fact that they are all completely round and all the same size (and that their color and luster are the same, and no overtones) makes me think they may be imitation.
I don't think they are akoyas. 9.5-10.0mm is...
1. Are they all completely round? Some look a bit oval in the photos.
2. Rub two of them together gently. Do they feel gritty or smooth?
3. You said 9.5-10mm. Are they all the same size in fact, or are some just a little smaller than others?