In setting out and working- a diminished twisted column for masonry, first set out the column to the extreme diameter of outside of wreath or roll, with the diminish and entasis as in an ordinary column. Having decided how many times the wreath is to encircle the column, set ont the spiral to a developed line. If a piece of paper is cut the shape of a right-angled triangle, the height of the perpendicular being- equal to the height of the cylinder, the hypothenuse (or long side of the triangle) will generate a curve winding round the cylinder in the form of a spiral. This curve is called the helix, and is the developed, line of centre of wreath or roll required. In order to illustrate this more clearly, take two long ribbons of paper cut parallel, one piece being white and the other piece black; wind first, say, the white round the cylinder, leaving a parallel space just sufficient for the black piece, which now wind round the vacant space, touching perfectly each of the edges of the white band. This being done,let the white band represent the roll and the black hand the hollow, or vice versa. This example applies to a cylindrical shaft whose ends form equal parallel circles.

In the case of the tapering column the developing of the spiral line will require great nicety in the setting out; and although the band will not be quite parallel, the principle is the same. The shaft is first worked as a plain column to the extreme or outer diameter. The spiral line is then traced round the shaft, and the hollow worked out. Lastly the roll is rounded off, each process being gaided by reverses or templates.