Wash cucumbers. Slice into thin slices using a mandolin or other grater for even slices (cut them as thick or as thin as you like your pickles to be)

Peel onions and slice thin as well.

Place the sliced cucumbers and onions in a large stainless steel bowl or a pickle crockery if you have one. Sprinkle with 1/2 cup of pickling salt, then toss gently with your hands to distribute the salt evenly. Let the mixture sit for 3 hours, then drain well but do NOT rinse.

Combine the vinegar, sugar, mustard seed, celery seed, and turmeric if using in a large stainless steel pot. Heat over medium high heat, stirring to combine. When the mixture comes to a boil, add the cucumbers and onions. Return to a low boil over medium heat, then pack immediately into hot, sterilized pint jars, leaving 1/2 inch headroom.

Wipe the jars clean before placing lids and rings on. Process the jars in a hot water bath (185 F / 85 C) for 10 minutes. If you are canning at a high altitude, you may need to adjust water processing time. Remove carefully and cool upright naturally. The flavor will develop over several weeks.