Fill water bath canner with water and turn on to heat water.
In a large pan, add the grape juice and pectin and stir to disolve the pectin. Add butter (optional) to reduce the foam.
Bring the mix to a full rolling boil. A boil that cannot be stopped by stirring. Let it boil for 10 minutes of medium heat.
Add the sugar and then stir out and let disolve.
Bring back to a boil. Let boil for 1 minute. A rolling boil is a boil that canning be stirred down. Stir constantly.
Remove from the heat.
Skim off any foam that is on the jelly.
Ladle the jelly into the jars using the canning funnel (keep the jars clean)
Fill to 1/4" headspace
Wipe the jars rim with a clean wet towel
Place the seals and bands on the jar.
Process the jars in a water bath canner for 10 minutes. Let the jars sit for 5 minutes before removing and placing a towel over them on the counter while they cool.
Label and date the jars. Remove the bands for storage and check that the seals do not lift up.
If the jars don't set, you can reprocess in the waterbath again for 10 minutes or add 2 Tablespoons of pectin and reprocess to a boil and waterbath again. You can only reprocess within the first 24 hours.