Wash cucumbers well. Trim a sliver off both ends of the cucumbers, then cut width-wise into 5 mm (¼ inch) round slices. Put in bowl.
Peel onion, slice thinly. Add to bowl.
Sprinkle with salt OR salt sub, toss gently with hands.
Add a half dozen ice cubes, toss again, then put a layer of ice cubes or crushed ice on top.
Refrigerate (if possible) for 3 to 4 hours, or overnight.
In a very large pot, mix together the ingredients from the vinegar down to and including the turmeric.
Bring to a boil, then reduce to a simmer covered for 10 minutes.
Drain the cucumber well (including any stray hidden ice cube pieces in it), then add to the vinegar mixture.
Increase heat on the pot a bit and let the mixture just come to a boil again.
Using a slotted spoon, pack cucumber and onion slices into half-litre (US pint) or 1 litre (US quart) jars, leaving 2 cm (½ inch) headspace regardless of jar size.
Add ⅛th teaspoon Pickle Crisp per jar. (optional; double for litre/quart jars)
Divvy out vinegar liquid amongst jars, leaving 2 cm (½ inch) headspace.
Debubble, adjust headspace.
Put lids on.
Process in a water bath or steam canner.
Process either size jar for 10 minutes; increase time as needed for your altitude.