Thank you Lilliefuzzysocks.
Each kind of pearl looks better using a specific pattern. If I carve a white pearl (this one is smooth pale yellow coloured) as the tahitian, light will not play as it would have to do, and by reverse, matter of material is the best way to carve tahitian pearls (which have also the right thickness of nacre to allow that). Lavender and purple pearls must be worked, carefully, between the two, and, at last, baroque pieces ask a design according to their shapes, of course.