Should plastic mold recipe be in more books?

Unfortunately I cannot locate the reference I used when making the original PR, but the links given by @AssumeCroons are all very similar to what I had in mind. The mold was supposed to be a clamshell mold. AFAIR we didn’t have clay back when I made the original PR (back in 2013), and neither do we have a silicon/plastic distinction. So either changing the outer material to silicone explicitly as in e.g. (which certainly wasn’t my original ref, as it wasn’t around in 2013), or changing it to clay are fine.
The use of the mold was supposed to be limited to very simple, generic things like bottles, bowls and bags. Electronics are certainly too complex for the simple clamshell to do and would need completely separate tools.
(This old PR really makes me wish we had “programmer notes” similar to “translator notes” so that we could put references in - I remember explaining several times in the intervening years just why the chemistry set has copper wire in it, for instance)