I had 0 bonecraft. Synthed this to level 1 and never got another skill up in 2 stacks of product.
I dont' have the ability to test the Vongola Clam (not the easiest to obtain); however, i got that recipe at level 1 from one of the basic support NPCs (not the advanced support). I would guess that cap is level 1 or level 2 only.
I'm level 5 bonecraft. I am now getting both Shell Powder recipes from the Mithra near the desk in the back. I'm assuming I'm within 1-2 levels of the Vongola Clam recipe, and 3-5 levels from the Seashell recipe. I will post more info (and hopefully exact recipe caps) as I continue to skill up bonecraft.
There are two ways to make this, both using Wind Crystals.
The first is via 3 Seashells, the second is by 2 Vongola Clams. Both recipes are given to me by the NPCs at the guild with a 0.0 in Boneworking.
Seashells are probably easier to get, seeing as the guild sells them.
Shell Powder is used in Seiglinde Putty, which is necessary to turn your Sunbreeze-gained Goldfish Set into a Goldfish Bowl. This does mean that people will need to perform this craft (or have it done for them) at some point, and as such it looks like SE is pushing people toward crafting with the first part of this event.