Wash and scrub cucumbers clean. Cut the ends off, then cut into 1/4-inch slices.
Layer cucumber slices, shallots, and ice cubes in a large deep glass or stainless-steel container or bowl.
Dissolve the pickling salt in the 12 cups of water, then pour over the cucumber mixture. Add more water if necessary to cover. Place a plate on top, and add heavy objects on top to weigh it down and keep cucumbers submerged. Let stand for 30 minutes or for up to 1 hour.
Drain and rinse well. Drain again, gently pressing down on the cucumbers to squeeze out as much liquid as possible.
Sterilize the jars: First, wash your jars and lids in hot water with detergent and rinse thoroughly. For this recipe, you'll need at least 6 2-cup (500 ml) canning jars. After washing, place empty jars (right side up) in a boiling-water canner* with the rack in the bottom. Fill the canner with water until it is 1-inch above the tops of the jars. Bring to a boil and boil for 10 minutes. Reduce heat to low and keep the jars in hot water until ready to fill. Note: If at an altitude higher than 1,000ft, add 1 minute of boiling for each additional 1,000 ft.
*If you don't have a boiling-water canner, you can use a large flat-bottomed pot instead.
In a saucepan, bring vinegar, water, sugar, mustard seeds, salt, celery seeds, coriander, turmeric, and cloves to boil, stirring until sugar is dissolved.
Use tongs to carefully remove the jars from the hot water. Use oven mitts or a towel while handling the jars to protect against burns. Tightly pack cucumber mixture into still-hot jars to within 1 inch of rim, then cover with liquid, leaving 1/2 inch headspace. Use a wooden spoon or chopstick to remove any air bubbles from the jars. Simply insert and gently wiggle around to release any air bubbles trapped inside.
Note: It's best to use wooden or plastic utensils for this step, as anything metal could scratch your jars, shortening the lifespan of your jars. Cover jars with lids cleaned in boiling water. If using screw-tops, screw on the bands until resistance is met, then increase to fingertip tight.
Fill canner* halfway with clean water and heat to 140°F (60°C). Place sealed jars in the rack and lower into the heated water, or fill the canner one jar at a time, using a lifter to lower them into the canner. Make sure the water level is 2 inches above tops of the jars; if not, pour in more boiling water for. Cover and bring to a boil over high heat. Once boiling, boil continuously for 10 minutes, then turn off heat, uncover canner, and let sit for 5 minutes. Lift up rack, and with canning tongs, transfer jars to cooling rack; let cool for 24 hours.
*Note: If you don't have a boiling-water canner, you can use a large flat-bottomed pot. Wrap a thick elastic band around a pair of tongs to use to transfer the sealed jars to and from the pot.
Once completely cooled, store pickles in the fridge at least 1 week before opening. Will keep well for at least 1 month in the fridge.
*If you don't have pickling salt replace with 1/4 cup of kosher salt.
*If you don't have a water-boiling canner, use a large heavy-bottomed pot instead. Wrap a thick elastic band around a pair of large tongs to use for canning tongs.