Prepare Pomona's calcium water by mixing ½ cup of water with ½ teaspoon of calcium powder. Stir and set aside. You won't need to use all of this and the extra calcium water can be labeled and stored in your fridge for future use. Use within a few months.
Fill a water bath canner (or large pot with a rack at the bottom) half way with water and submerge 6 or 7 half pint canning jars. Sterilize the jars by bringing the water up to a simmer. Also, bring a separate saucepan filled with water, the canning jar lids, and rings to a simmer.
In a medium saucepan, combine 4 cups of muscadine juice (plus a smidge more), ¼ cup of fresh lemon juice, and 4 teaspoons of calcium water. Whisk well and bring to a rolling boil over high heat.
In a separate bowl, mix together 1 cup of sugar and 4 teaspoons of Pomona's pectin. Set aside.
When the muscadine juice mixture is boiling rapidly, add the sugar and pectin mixture and whisk vigorously for 2 minutes until all the sugar is dissolved. Your arm will get a workout! When the timer goes off, remove from heat.
Set your sterilized canning jars on a kitchen towel. Ladle hot jelly mixture into your hot jars leaving ¼ inch of headspace at the top.
Wipe the jar rims clean and make sure there are no nicks or cracks that would prevent your jar from sealing properly. Then use a magnetic lid lifter to add the lid and ring to the jar. Tighten the ring until it's fingertip tight. That means that when you first meet resistance screwing on the ring, tighten a fingertip width more. Avoid over-tightening or your jar will crack during processing.
Use caution and a jar lifter to submerge the hot jars into the hot water bath canner. Add the canner lid and bring the water to a boil.
When the water is boiling rapidly, add the canner lid and set a timer for 10 minutes (adjusting for elevation) to process your jars.
After 10 minutes, turn off the heat and let the canner rest undisturbed for 5 minutes.
After 5 minutes, carefully remove the canner lid to avoid steam burns, and remove the jars with your jar lifter. Place the hot jars on a kitchen towel and allow to cool down for 12 to 24 hours. Listen for the satisfying "pop" of the lid, which signals that your jars have sealed properly.
When your jars have cooled down completely, remove the bands, check that the lids sealed properly, and then label and store your jars in a cool, dark place.