Just riffing off the top of my head here: I think your reflections will be very important, very subtle, but definitely needs to be a factor. A hard specular area. A hint of Sub-surface scattering so the very edges have some transmission through the material. I also wonder if it doesn’t pay to do it as 2 pieces of geometry.
Like you’ll find in the better ‘eye’ tutorials. Where there is a sphere for the iris and such, then a seperate larger sphere to have a glassy outer coat. I would think the iBooks would be similar. Where there is a simpler white layer, then a more reflective outer layer with very subtle abrasions added in. I’ve never seen an iBook (even a new one) with a pefectly flawless outer coat. It always has some small variation like finger prints or subtle scratchces here and there.
Just some thoughts.
Chris Smith
https://www.sugarfilmproduction.com