Prepare your calcium water by combining 1/2 tsp calcium powder with 1/2 cups water.
Prepare jars, lids, and bands.
Chop rhubarb into 1/2 inch pieces and place in a small sauce pan with the 4 cups of water. (Skip this and go to step 4 if you are using a steamer juicer to extract the juice from your rhubarb). Simmer for 15 minutes or until the rhubarb has broken down completely. Strain through a fine-mesh strainer or put mixture in a jelly bag to extract all of the juice.
Measure 4 cups of rhubarb juice and the seeds from 1 vanilla bean into a large sauce pot. Add the calcium water and mix well.
Measure out your sugar into a bowl. Mix the powdered pectin into your sugar.
Bring juice to a full boil. Quickly stir in the sugar/pectin, stirring constantly for 1-2 minutes until the mixture returns to a full boil. Remove from heat.
Fill hot, clean jars with the jelly, leaving 1/4" headspace. Process in a boiling water canner for 10 minutes. Let jars cool completely for 24 hours; check seals and store in a cool, dry, dark location.