Remove the zest from the tangelos using a zester, and wrap in muslin cloth or a clean chux cloth. Set aside until required.
Cut the tangelos into quarters and process in a food processor until finely chopped (a little rough is fine).
Place the tangelo mixture into a saucepan, along with the wrapped zest, water, tartaric acid and lemon halves. Cook for 1/2 hour or until zest is soft. Remove the zest in the bag and set aside.
Continue to cook the mixture for a further 1 1/2 hours.
Once the tangelo mixture has cooked for a total of 2 hours, strain mixture reserving the liquid.
Return the liquid to the heat, empty the contents from the muslin bag into the liquid, add the sugar and continue to cook the jam for a further 40-50 minutes.
Test for setting by spooning a little onto a chilled saucer. Continue cooking until the marmalade reaches setting point. Allow to stand for 5 minutes then pour into sterilized jars. Seal when cold.
To sterilize jars in the micro, fill with water and microwave on HIGH until the water boils. Remove from the oven, empty and invert on paper towels.