Egg crock

We are clearing out my mother in law's house as she has downsized. Apart from hundreds of books and small items, along with the furniture we came across this old style egg crock.

Google egg crock nowadays and you get a modern kitchen device. This is the old style crock where eggs were coated in isinglass or some other substance that allowed eggs to be preserved for many months.

I understand that they were better for baking than hard boiling but at least they allowed a glut of eggs to be kept.