The reason that it took me so long to get around to making one wasn't because of the effort involved in physically making it, it was all down to finding the right jar. I kept looking around for square jars just the right size for a cube (without too much wiggle room), but for some reason they always eluded me. This is when I turned to my old friend: eBay.
I found a square jar on eBay, checked the size was okay and placed the order, within two days it had arrived. Immediately I knew something looked wrong. It turns out (being the genius that I am) I didn't realise that most (sane) people when looking at jars aren't looking for measurements of the inner dimensions. The jar turned out to be way too small for a standard size Rubik's brand 3x3 cube.
While being a bit annoyed at myself I decided that I didn't want to waste a perfectly good jar, so I began to dig through my boxes of puzzles, and I found a cheap knock-off cube with what I can only describe as the most perfect dimensions to fit into the little jar. Lucky or what? And 30 minutes or so later I had a fully functional puzzle well and truly stuck in a glass jar.
The process is actually not very difficult, but like with many impossible objects it does require a decent bit of patience to achieve.
A great bit of fun that I'd recommend anyone with too much spare time (and a jar) on their hands to try for themselves.