Wow, these look wonderful!
Regarding your questions about the dark matrix in turquoise. I really am not the go to guy for good answers Martine. Most of my beads I collected in Tibet during better times and I believe the matrix is natural in them. However during that time floods of treated turquoise began to show up. I was interested in the best quality I could find and avoided it but now it is everywhere and old authentic stones are now very scarce. As evidenced on this forum it is widely misunderstood that much is clear. Evaluating beads from photos on the internet is not easy so a definitive answer will not satisfy all questions. I am primarily a collector and am out of the game now as the game has changed so I am sure Jamey or Danny could elaborate what this means currently & better than I ever could so I would go to the mountain. I will try to offer authentic material when I post so go with that and if someone can elaborate on your questions this thread could break the speed limit!
Peace & Beads 💜