Wash the cucumbers thoroughly, trim the ends, and slice them evenly into rounds about 1/4 inch thick. Thinly slice the onions so they soften at the same rate as the cucumbers.

Layer the cucumber slices and onions in a large nonreactive container, sprinkling the canning or pickling salt between the layers. Cover the vegetables with ice and let them stand for about 3 hours to draw out excess moisture and support a firm texture.

Drain the cucumber and onion mixture thoroughly after chilling. Do not rinse unless the vegetables seem excessively salty, since rinsing can remove needed flavor and may leave the pickles less seasoned.

Combine the 5% acidity vinegar, sugar, mustard seeds, celery seeds, and ground turmeric in a large pot. Bring the seasoned liquid to a boil, stirring as needed until the sugar dissolves.

Add the drained cucumbers and onions to the boiling pickling liquid. Heat until the mixture returns to a boil, then simmer briefly for about 5 minutes; avoid prolonged cooking because excessive heat can soften the vegetables.

Pack the hot vegetables into sterilized hot pint jars, leaving about 1/2 inch headspace in each jar. Cover the vegetables with the hot pickling liquid, then remove air bubbles with a nonmetallic utensil.

Wipe the jar rims clean and apply the lids and bands according to the lid manufacturer’s instructions. Process the filled jars in a boiling-water canner for 10 minutes at 0–1,000 feet elevation, increasing the processing time as required at higher elevations.

Move the jars to a towel-lined surface and let them cool undisturbed for 12–24 hours. Check each seal before labeling and storing, and refrigerate any jar that does not seal properly.