Some techniques. Paper clay making.

Tear toilet tissue into pieces and leave soaking over night.
Once they have turned into sour milk kind of mix blend well to separate even more.

Use thin fabric to siv out fistfuls of paper porridge.

To prepare the clay you have to break tiny thumb size pieces of dry clay into water and let soak over night again. Use blender to mix well.
Crumble small pieces of paper into the clay mix and blend in from time to time.
Do not mix clay slip and paper together if you want to start using it further in the future as it may start stinking.

Use soft kidney tool to apply the mix to the plaster cast in lairs. It dries fast so do not wait too long getting it off.

Use the edge of soft kidney tool to flick up the edge of the lair of paper clay and then you can just pull it off.

Once you have the paper clay sheets ready you can keep them covered with plastic and use to make forms that after firing are lighter. The paper would of burned away.