Start by combining cucumber, onions and salt in a non-reactive glass or stainless steel bowl.  Toss the vegetables in the salt to fully coat and let them sit for 2 hours.

Prepare a water bath canner, jars and lids while the cucumbers are soaking in salt.

In a stainless steel saucepan, combine the remaining ingredients including vinegar, sugar, mustard seed, celery seed and ground turmeric.  Note that all the salt in the recipe is used to soaking the cucumbers and is not added to the pickling brine.

Bring the pickling brine to a boil.

Strain the cucumbers and onions, and rinse them in the sink to remove most of the salt.  Drain them thoroughly.

Add the strained vegetables to the boiling brine and allow the mixture to return to a boil.

Once the mixture has boiled, scoop the cucumbers and onions out of the brine and pack them into prepared canning jars leaving 1/2 inch headspace.  Fill the canning jars with hot brine, still leaving 1/2 inch headspace.

Wipe rims, remove air bubbles and seal the jars with 2 part lids to finger tight.

Process in a water bath canner for 10 minutes and then turn off the heat and leave them to sit for another 5 minutes before removing the jars from the canner.

Allow the jars to cool completely before checking seals and removing canning bands for storage.