There are way too many styles of bikini top to describe them all here. I’ll stick to some simple variations of the gathered bikini I described yesterday.
Perhaps the easiest thing to add is a small strip of fabric covering the gathers. This gives the top a sort of bow shape. Cut a piece of fabric twice as wide and twice as long as you want the center of your bow to be. Fold it in half lengthwise with the right side facing in and sew up the side. Fold it right side out, wrap it around the gathers in the middle of the top, and sew up the other end.
Another easy modification is to add a more substantial back. Cut a rectangle of fabric as long as your back (accounting for the fabric stretch), and sew it to both sides of the front. Shown above with elastic straps attached in front and in back and bellow with the usual straps sewn on in front and tied as a halter. The swimsuit bellow has a tapered band (smaller in the middle, larger at the sides) rather than a simple rectangle.
A tie front is a slightly more complicated modification, but still quite manageable. I’ve sketched the shape of the front pieces. Cut two pieces in this shape from the main fabric and two more from the lining. Sew the lining to the main fabric, turn right side out, and sew to the back (or straps) as usual. Tie the front.
Next week: How to make a one piece.