OK, Bone Helmet Material...

It's one of those things that looks like it might go somewhere, but so far I've just managed to destroy a lot of materials. So here's the list of items I've combined with Bone Helmet Material. Most of them return Leather Lv1, which seems to indicate that the combinations I've tried so far are all invalid.

Bone Lv1
Claw Lv1
Clay Lv1 & Lv2
Fang Lv1
Flower Lv1
Grass Lv1
Horn Lv1
Leaf Lv1
Leather Lv1
Leather Lv2
Scale Lv1
Sea Shell Lv1
Shell Lv1
Stone Lv1
String Lv1
Wing Lv1
Wood Lv1 & Lv 2
Crystal Lv1
Burning Charcoal
sturdy hat