Prepare the cucumbers. Cut ¹⁄₁₆-inch off the blossom end of each cucumber and discard. Cut into ¼-inch slices. Combine cucumbers, onion, and salt in a large bowl. Mix to combine and cover with ice cubes. Refrigerate for 4 hours, adding more ice as needed. Then, drain the cucumbers and onions.

Prepare the water bath. Get ready 8 pint jars, lids, and rings.

Prepare the brine. In a 4-quart kettle, combine the vinegar, water, sugar, turmeric, cloves, celery seed, mustard seed, and red pepper flakes. Stir to dissolve the sugar and bring to a boil. Reduce to a simmer to keep the brine warm.

Prepare the jars. Pack sterilized jars with drained cucumbers and onions, leaving ½-inch headspace. Pour brine over prepared cucumbers and onions, still leaving that ½-inch headspace. Wipe the rims of the jars with a clean cloth to remove any drips. Place on lids and rings, tightening to fingertip tightness.

Place jars in the boiling water bath. Bring back to a boil and boil for 10 minutes. Check with the USDA canning guide and adjust the processing time for altitude.

Remove from the water bath and cool for 12 to 24 hours. Remove rings to ensure a good seal and store for up to one year.