The function of the bond in moulding sand is that it should make the sandsufficiently plastic for moulding and give it sufficient strength in thegreen (moist) and dry states after compaction to retain its shape and laterto support the weight of the metal. It must do this while still leaving thesand permeable to gases, and it must further retain its strength in contactwith the hot metal for a sufficient time for it to solidify, after which itshould be sufficiently weak to be readily removable from the finishedcasting.