I am a hobbyist with no education in electrical engineering. I am working on a DIY project trying to make water resistant rechargeable bicycle lights. I am doing this as a hobby for fun and learning so it doesn't need to be commercially viable or to pay off. The device will be cast in silicone and will be completely covered so it needs wireless charging. Because of the size of it I cannot use any coils or wireless charging solutions I can buy, so I am attempting to make my own. As far I have come up with etching the charging coils in layers on copper foil that seems to work for me surprisingly well(as far at least):
I understand I could improve the energy transfer by having many layers close to each other and the right AC frequency and I am trying to improve there, but as I understand having ferrite plates beneath the coils could improve things dramatically. Unfortunately the plates need to be very specific size and shape for my project and it is not practical to buy or order them. I am looking for a way to make something similar at home. My main question is: what are my options, if they exist at all? In this context it doesn't need to be perfect, it needs to be better than nothing.
Research as far and ideas
I have looked into making ferrite at home and found this: Make Your Own Ferrite to Improve Magnetic Fields, however on further reading about making ferrite I got the impression that crystals of iron oxides and a small amounts of some other metal need to be formed so I started to doubt that this really works without high pressure and temperature. Could someone confirm if this DIY method really works or is this nonsense?
I also have an idea to buy ferrite beads, crush them into powder and then cast my needed forms from that using some adhesive like silicone or PVA glue. Would that work?
Are there any other options?