Mix together in a bowl all the dry ingredients including dates and walnuts (leave out only the buttermilk, honey, orange half and rhubarb). Put the buttermilk and the honey in the blender. Wash an orange, cut off any price or brand marks and cut it in half. Cut the orange half into chunks and add it to the blender, being sure that you have removed all the seeds. Run the blender until the orange chunks are chopped into little bits. Now add the buttermilk mixture, along with the rhubarb chunks, to the dry ingredients and mix well.
Pour immediately into greased cans, filling each can no more than two-thirds full. Cover the filled cans with aluminum foil, and secure the foil with a rubber bands. Place them in a large pot, on some kind of a rack so they are not touching the bottom of the pot. Pour in hot water until the bottom 2 inches of the cans are covered. Bring to a boil and keep the water boiling gently for about 1 1/2 hours.
The pot should be covered and there should be a little steam escaping at all times. Check the pot occasionally to make sure that there is enough water left.
At the end of 1 1/2 hours, check with a skewer, right through the foil. If it does not come out clean, cook for another half hour and recheck. When the loaves are done, take the "hot" cans out of the pot. When you are ready to serve, uncover a mold, shake the loaf out onto a breadboard and slice it. Serve warm with butter or cream cheese.