Have a large bowl at hand, containing cold water and the juice of two lemon with the four halves of the rind. Keep the artichokes in another bowl of cold water while you are working on them. Take one artichoke at a time, drain it, and pull off and discard the smallest outer leaves. Holding the artichoke with its bottom toward the little finger of your hand, tilt the top away from you, and holding a small sharp knife tightly with your right hand, insert its tip, one leaf deep, into the tender, lighter part of the leaves. Keeping your right hand steady, slowly rotate the artichoke with your left hand so the bottom moves in a clockwise direction, and cut upward in a spiral. The tough part of each leaf will fall off, while the tender edible part remains attached. Peel the green layer off the bottom and stem, and then drop the trimmed artichoke into the lemon juice until you are ready to cook. This operation requires some practice; you will know if you have mastered this technique when the artichoke thus cleaned looks more or less like the one you started with, only smaller and whiter.
If you are not ready to use the artichokes immediately after you have cleaned them, try to keep them completely submerged in lemon water. This is not easy. Artichokes are very buoyant and float to the surface making it difficult to keep them covered. An inverted plate, just a bit smaller in diameter than the bowl, place over the artichokes, will keep them below the surface. Another way is to crowd them inside a glass jar and cover them with the lemon water. If you plan to leave them at this stage for more than a hour or so, you must refrigerate them, but it is not advisable to keep artichokes this way for more than a few hours. Lemon is used to prevent discoloration; on the other hand, the lemon will cause the artichokes to spoil very quickly."