[opencl]

Ferrofluid has been used in certain high end speakers for quite a while, it can break down or dry out eventually but generally lasts well over a decade in that application.

The glass treatment is just to prevent the ferrofluid from sticking.

[mr_sturd]

Thank you. I remember seeing someone had made a clock face using ferrofluids, and wanted to give something like that a go myself, but was put off hearing the information I was questioning.

[zamalek]

The smaller detail that really clinches it here is suspending the ferrofluid in another fluid. I have seen at least one of the clocks, and the ferrofluid doesn't behave nearly as nicely in air.