> Because titanium is opaque, solid titanium looks the same as a thin shell of titanium on top of another material.
I obviously haven’t done the math and don’t have access to the data that would allow me to, but I suspect that for this application, you’d have to have an extremely compelling reason to complicate design and manufacturing with such an approach.
Most people would consider not burning their eye socket and possibly brain an extremely compelling reason. Heating an entire 7-cc titanium ball from 37° to the 44° necessary to start causing burn damage would take about 30 joules: 500 mW for a minute, for example. If the heat source is close to the surface of the eyeball (on the inside) you would need less energy because only a part of the eyeball is reaching burning temperatures, maybe as little as a joule. If the ball is almost entirely full of water and properly insulated, you could probably handle hundreds of joules before it started to burn you through the teflon or whatever. A hundred joules is a 3.7 volt Li-ion battery with 7.5 milliamp hours of capacity, so this is a practical amount of energy to put inside your eye socket.
I obviously haven’t done the math and don’t have access to the data that would allow me to, but I suspect that for this application, you’d have to have an extremely compelling reason to complicate design and manufacturing with such an approach.