First the glass is protected with cutoffs of bubblewrap and cling film wrapped around the whole thing.
Then sheets of bubblewrap are applied and the edges protected with folds of cardboard to take pressure off glass front, and wrapped again with cardboard to double protect.
Then the wrapped painting is placed in the packing box, like a large cardboard envelope, with the front facing the address side.
Finally the whole package is closed and secured with stickers, ready to be addressed and sent off