Take fresh spinach or beet leaves, and pound them in a marble
mortar. If you want it for immediate use, take off the green froth
as it rises, and mix it with the article you intend to colour. If
you wish to keep it a few days, take the juice when you have
pressed out a tea-cup full, and adding to it a piece of alum the
size of a pea, give it a boil in a sauce-pan.