Wash cucumbers. Cut 1/6-inch off blossom end and discard. Cut into 3/16-inch rings.
Combine cucumbers and onions in a large bowl. Add canning salt.
Cover with 2 inches crushed or cubed ice. Refrigerate 3 to 4 hours, adding more ice as needed.
To Make Pickles: Add sugar and remaining ingredients to vinegar in a large pot. Boil 10 minutes. Add well drained cucumbers and onions and slowly reheat to boiling. Fill pint or quart jars with cucumber & onion slices, leaving 1/2-inch headspace. Fill to 1/2 inch from top with hot cooking liquid. Remove air bubbles. Wipe jar rims. Adjust lids.
Process pints or quarts for 10 minutes in a Boiling Water Bath. After processing and cooling, jars should be stored 4 to 5 weeks before use to develop ideal flavor.
