I don’t hanker after the days of trying to cast conversions in cuttlefish (I never believed this was a real thing, but thanks to the internet, apparently…) but I have an inveterate nosiness
Well I never expected that. Stimulated by invertebrate nosiness, I had a quick google, which fished up this piece https://www.ganoksin.com/article/cuttlefish-casting-method/ on the use of cuttlebones in moulding, so I am logically compelled to admit that it is A Thing. Why exactly one would wish to use such a thing in preference to conventional casting materials escapes me, so without casting any doubt on its basic thingitude I beg leave to doubt whether it is a sensible thing.
One of the handy hints in the linked article is easily the daftest thing I’ve read so far today:
“The model is given shape with hammers, files and any other tool necessary.”
I suppose that’s the logical follow-on to the advice that you can make a sculpture of an elephant by taking a piece of marble, and cutting away all the bits that don’t look like an elephant.
All the best,