Blowing my own horn
My horn shape pulled out of the plaster cylinder so smoothly so it didn't need cutting. Hooray.
It looked really mystical as it smoked steam because of the plasters exothermic setting process.
I will leave it to dry until next week and then test it. If I am happy with how it slip casts then I will make a few more so I can reproduce several horns at once as I'd really like a while collection of them glazed interestingly that I can then curate into an installation.