Set up your water bath canner and bring the water to a simmer. Wash pint jars in hot soapy water and keep them hot until you're ready to pack. Have your lids and bands ready alongside the canner.

Tie the pickling spice in a square of cheesecloth to make a small spice bag. (You can simmer the spices loose if you don't mind some sediment, but the bag keeps the brine cleaner and prevents whole spices in the jars.)

Combine the vinegar, water, sugar, and pickling salt in a large non-reactive pot. Bring to a boil over medium-high heat, stirring to dissolve the sugar and salt. Add the spice bag, reduce the heat, and simmer gently for 15 minutes to let the spices infuse the brine.

While the brine simmers, wash the cucumbers under cold running water and drain. Trim about 1/16 inch off both ends of each cucumber, then slice them lengthwise into 1/4 inch slices.

To each hot pint jar, add 1 bay leaf, 1 garlic clove, 1/2 teaspoon mustard seeds, and 1 head of fresh dill. Pack the cucumber slices into the jar tightly without crushing, leaving 1/2 inch headspace.

Remove and discard the spice bag. Ladle the hot brine over the cucumbers, maintaining 1/2 inch headspace. Run a bubble remover or chopstick around the inside of the jar to release trapped air, and add a little more brine if needed. Wipe the jar rims with a clean damp paper towel, center the lids, and screw on the bands to fingertip tight.

Process pint jars for 15 minutes in a boiling water bath canner, adjusting for altitude (see notes). The canner water should cover the jars by at least 1 inch, and timing starts after the canner returns to a full rolling boil.

Turn off the heat, remove the canner lid, and let the jars rest in the canner for 5 minutes. Move them to a towel-lined counter to cool undisturbed for 12 to 24 hours. Check the seals, label the jars, and store sealed jars in a cool, dark place. Wait at least 2 to 3 weeks before opening so the flavor has time to develop.