Slice cucumbers and onions into thin rounds.

Combine sliced cucumbers and onions in a large bowl.

Cover the cucumbers and onions with ice water and salt.

Let the mixture soak for at least 3 hours, ensuring the vegetables are submerged.

In a large pot, scald the vinegar over medium heat.

Add sugar, mustard seed, turmeric, and celery seed to the scalded vinegar.

Stir until the sugar is completely dissolved and the spices are well incorporated.

Drain the cucumbers and onions thoroughly to remove excess water.

Add the drained cucumbers and onions to the pot with the vinegar solution.

Heat the mixture through, ensuring it doesn't boil.

Carefully transfer the hot pickle mixture into sterilized jars.

Ensure the cucumbers and onions are fully covered with the vinegar solution.

Seal the jars tightly.

Process the sealed jars in a boiling water bath for the appropriate time based on your elevation and jar size to ensure proper preservation.