Add pickled artichokes to salads or an antipasto platter.
In a large bowl, combine lemon juice and 2 cups of water. Remove tough outer leaves from artichokes and cut across tops about 1 inch from heart. Trim stems to remove dark tough skin. Cut away any bruises or bad spots. Place artichokes in lemon water.
Wash 4 one-pint canning jars, lids, and screw bands in hot, soapy water and rinse well. Place jars upright on a wire rack in the bottom of a large pot. Fill pot with hot water until jars are submerged by 1 to 2 inches, and bring to a boil. Boil for 15 minutes. Turn off heat; leave jars in water. Sterilize lids according to manufacturer's instructions.
Combine vinegar, 1 1/2 cups water, salt, garlic, and sliced lemon in a large pot and bring to a boil. Drain artichokes, add to pot, and simmer for 1 minute.
Using stainless-steel tongs, remove jars from water and place on a layer of clean towels. Divide peppercorns evenly among jars. Add 5 sprigs thyme to each jar. Using a clean slotted spoon, remove artichokes, garlic, and lemon slices from pot and pack tightly into jars, pressing them down with the back of a clean spoon. Leave 3/4 inch of space beneath the rim of the jar. Pour hot liquid over artichokes, covering them by 1/4 inch and leaving 1/2 inch of space at the top of each jar. Slide a clean plastic chopstick or wooden skewer along the side of the jar to release any air bubbles. Wipe mouth of jar with a clean, damp cloth. Place hot lid on jar; screw on band firmly without forcing.
Place a wire rack in the bottom of a large pot and fill partway with hot water. Using a jar lifter, place the jars on the rack. Add enough hot water to cover by 2 inches, and bring to a boil. Boil for 10 minutes. Remove jars from water bath with jar lifter; let stand on clean dish towels for 24 hours. Check cool jars for the slight indentation in the lids that indicates a vacuum seal. Jars that do not seal properly or that leak during processing should be stored in the refrigerator and pickles consumed within a week. Allow sealed pickles to mellow in a cool, dry place for a few days before serving. Store opened jars in the refrigerator.