This section is from the book "Clothing For Women: Selection, Design, Construction", by Laura I. Baldt. Also available from Amazon: Clothing For Women: Selection, Design, Construction.
(1) To add to the center back of a gored skirt place back of pattern with front edge on lengthwise thread of goods. If plaits are being added to the seams, allow for these. Then place the long arm of the square along the center back. Add two to three inches at the waist, and twice that much to the bottom, plus the seam, draw in the line and mark center of plait and seam and fold before cutting out at waist line (Fig. 67A and B).
To design this skirt, place front of pattern as before and add once the width of the plait plus the seam to the bias edge of the front, and three times the width of the plait plus the seam to the front edge of the side gore; then add once the width of the plait plus the seam to the bias edge of the side gore and three times the width of the plait plus the seam to the front edge of the next gore. Repeat throughout the skirt, adding plait to center back (Fig. 670 and. D).
Cut two parts of skirt as for a plain skirt. Mark off on the back edge of the front of the pattern and the front edge of the back the width and height of the plaits to be set in. Draw lines on pattern through these marks. Slash across skirt from hip seam at the point indicating the height of and as much as the width of the plait and any desired shape. Fold material back on line indicated for width of plait. Repeat with other gore, pin hip seam as far as top of skirt and turn in edges of slash. Cut a strip of material eight times the width of the plait by its length, plus seams for joining to skirt. Fold plaits facing each other in material and baste; slip the plait just made into position, face edge of slash to top of plaits and seam plaits as in the other skirts.
Lay all the pieces of the pattern together upon a piece of drafting paper. Draw the outline of the panel, (which may be the width of the original), and the yoke on the pattern, and trace the outline of the panel and yoke; also the outline of the remainder of the skirt. Cut paper pattern apart, mark for joining, allow seams when cutting in material. For plaited side, trace hip seam and place for plaits according to any of the directions given above (Fig. 68D).
Shaped lower edge for use in plain material. Trace a circular foundation pattern one and one-half to twice the hip measure. Mark hip line; test hip measure. Divide the bottom of the pattern into equal parts, according to the type of plait desired - wide or narrow. Divide the hip line into the same number of equal parts. Draw heavy lines connecting these points. Lay a sheet of tissue or pattern paper along the front, pin, trace the fold of the first plait, then measure beyond the first fold of the pattern, once the depth of the plait desired, this for the inner fold of the plait. From this, once again the depth of the plait. Draw lines through these points and fold plait so that the line of first fold of the pattern touches the second width of plait measure. Repeat throughout skirt. Mark the space between hip and bottom accurately and fold plaits carefully. Use the pattern for cutting material (Fig. 68A. and B).