One time use alginate mould. You tear the alginate mould apart to get to your object. Also, as the water evaporates over time the mould shrinks if you succeed in keeping it intact.
Success in the learning and not the result. 😉 Here I forgot to pour in just a little plaster at first, twist and turn the mould to get the air out and the plaster into all the nooks and crannies of the mould before I poured in so much plaster that the mould was brimming.