Put rice in medium bowl with water to cover. Drain and repeat procedure 5 times. Return rice to the bowl and gently fill the bowl with cold running water. Keep the water running gently into the bowl until the liquid runs clear. Drain, return rice to the bowl with water to cover, and let stand for at least 6 hours. (Can let stand at room temperature overnight.) Bring 4 quarts of water with 2 tablespoons salt to boil in a soup kettle. Keep the water boiling while slowly adding the drained rice. Simmer for 5 minutes; rinse with cold running water and drain thoroughly. Remove 1 cup of rice and stir in the saffron threads; set aside. Put the plain rice in a large bowl. Peel a 3- by 1-inch strip of zest from the orange and cut into 1/8-inch dice. Bring 1 cup of water to boil in a small saucepan, add the zest, and simmer for 2 minutes. Drain the zest and pat dry. Heat 1 tablespoon butter in a small skillet and saute the zest for 15 seconds; add the sugar and cook for 30 seconds. Stir in cinnamon, pistachios, raisins, and 1/4 teaspoon salt; saute, stirring continuously to coat with butter-sugar mixture. Stir zest mixture into the plain rice. Melt the remaining butter. Coat the bottom and sides of a heavy, lidded, 3-quart saucepan (preferably cast iron) with 1 tablespoon of the melted butter mixed with the oil. Heat the coated pan until hot. Remove from the heat and spread half of the zested rice over the bottom of the pan, pressing down well with a spoon. Cover with a mound of the remaining zested rice. Sprinkle the saffron rice over the top. Use the handle of a wooden spoon to make a hole in the center of the rice deep enough to reach the bottom of the pan. Make 2 or 3 additional holes in the rice to allow steam to escape. Drizzle rice with remaining 4 tablespoons of melted butter. Cook rice for 6 minutes over low heat, uncovered. Wrap lid in a linen towel, securing towel ends under or around lid handle. Cover the pot with the towel-wrapped lid and steam over low heat for 40 to 60 minutes, until a crisp golden crust forms on the bottom of the rice. Remove pan from heat and let stand for 10 minutes. SERVING: Spoon soft, fluffy rice onto a platter. Break the bottom crust into pieces and arrange around the fluffy rice. Serve immediately