I had that copper nails for... wow... years! I remember when Karen sent me those that were part of her dad's work space with some old pliers and tools that I still use and are my favorite ones. -Yep, nothing like older tools my friends, they are almost eternal while modern ones break easily. 
I had the Shibuichi Jesus cast for a while in my Shibuichi castings bin and it just... "happened" like lots or most of the things happen at the studio. Nails, Jesus... 
The natural Large turquoise Kurt sent me from that closing store was Perfect for it... then just copper and more copper, fire, brazing, fusing, sanding, polishing -polishing is like painting in negative, one does not add color but removes the fire patinas here and there where light will explode with copper shine... like the kids art projects where one paints with crayons on a blank page, then covers it with China ink and then... scratches the drawing on the surface revealing the colors underneath... -
The focal element is not just the Shibuichi Jesus but also the nails, the spiral, the explosion of energy and life even in death in a Christian way while the neck piece resembles the thorns crown humanity carries.
(The focal and neck piece have the copper nails, the tips removed, sanded to death)
VERY solid, ends in a hand crafted clasp and to open it to put it on if your neck is wide, instead of opening laterally making bigger the opening, would be better to open it as a torque, grabbing one extreme with each side and pushing one hand up and the other down repeating the motion to close it back once around the neck. I can make a video if you need. 
It measures around the neck approx. -following the curve with a metric tape- 16 inches. It can't be extended -due to the double row of thick copper- but could be reduced a bit-