just trying to post some more pictures - the box is very thin and light - very light. The lid is a little heavier by comparison.
By comparison the Pāte de Verre head I own is a solid 3d piece and is very heavy.
I've still no idea what technique was used to make the box but in trying to find out I came across this fascinating link to the making of thin Pāte de Verre.
This is an absolutely amazing film covering the design, mold making and then finally the making of the bowls by Shin-ichi Higuchi:
Eggshell Thin Pāte de verre with Shin-ichi Higuchi | Master Class Series, Volume X
https://www.youtube.com/watch?v=PCYu7m1qM9k