We need to select materials with varying magnetic permeability.
Here is where we will have the spheres precisely manufactured.
1. AISI 1006 Carbon Steel (high permeability)
2. Alloy Steel 52100 (not as high permeability)
3. Aluminum Bronze C95400 (low permeability)
4. Titanium (zero permeability)
5. Neodymium (high strength magnet)
6. Acrylic (PMMA): (zero permeability) containing a cluster of 13 Neodymium (high strength magnets)