To make orange marmalade, first fill a boiling-water canner half full with water. Bring the water to a simmer. Wash canning jars and screw bands in hot, soapy water; rinse with warm water.
Place the flat lids in a saucepan and pour boiling water on top; let stand until ready to use. Drain the jars thoroughly.
Use a vegetable peeler to remove the peel from about four medium oranges and two medium lemons; cut into thin slivers. Mix and bring to boil in a large saucepan the peel, 2 1/2 cups water and 1/8 teaspoon baking soda. Lower the heat to medium-low and simmer, stirring occasionally, for 20 minutes. Add the fruit; cover and simmer for 10 more minutes.
Measure 4 cups prepared fruit into a 6- to 8-quart sauce pot. Stir in one box fruit pectin and 1/2 teaspoon butter or margarine. Heat the mixture on high to a full rolling boil, stirring frequently; stir in 5 1/2 cups sugar. Return to a full rolling boil for exactly 1 minute, stirring frequently. Remove from heat and skim off any foam with a metal spoon.
Immediately ladle the marmalade into prepared jars, filling to within 1/4 inch from the tops. Wipe the jar rims and threads; cover securely with lids and bands. Place jars on an elevated rack in the canner. Lower rack into the canner, cover, bring water to a gentle boil and process for 10 minutes. Remove and cool completely, checking lids to ensure a tight seal.