Sift flour, baking powder, salt, and sugar. Cut in shortening with fingers. Add currants and soda to mix and stir into flour mixture with a fork. Turn out onto a floured board. Knead slightly and pat or roll into 1 cm thickness. Cut into triangles or circles. Bake these on an ungreased griddle over medium heat. As one side becomes brown, turn and brown the other side, then turn each scone slightly on edge and place on side of griddle to the "fire". Turn until all edges are slightly browned. The firing will cook the scones through from all sides so there will be no raw dough in the center. Split and serve with butter, or fill with such as ham or cream cheese.