This is one my grandma used from the Fannie Farmer cookbook, It's real good.
Orange Marmalade
Use Tart seville type Oranges- or if using common oranges you can sharpen the flavor by adding a thinly sliced lemon.
Select unblemished oranges. Wash thoroughly. Slice as thin as possible, and remove seeds. Measure without draining. For each Quart of sliced oranges..add 1 1/2 quarts water and let stand overnight. Cook slowly until the peel is tender, about 2 to 2 1/2 hours. Measure the UNDRAINED Oranges and add 2/3 as much sugar. Cook rapidly to the jelly stage 30 to 60 minutes. Makes about 5 pint's.
I want to add that the recipe above is a purist old fashioned recipe. Some people dont like the taste of bitter orange peel in their marmalade (I do) so they peel their oranges and will also add orange juice in place of water to give deeper flavor. Some people add spices like cinnamon, clover etc...My grandmother used the recipe just as is. It is an original recipe that I love. You can experiment either way to get the taste you love. Good luck