a box that is lined with moist material for keeping clay in a plastic state.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for damp box
Various other expedients for drying cupboards, damp-box, etc., will suggest themselves as the course develops.
All work to be stuck up or modelled on should be kept in the damp-box until quite finished and then dried very gradually.