I got a question on Tumblr about my Jewel costume; I'm posting the answer here because it's easier for me to format. Without further adieu here's how I made my...
Jewel costume AKA the super spandex tube top
* 1-2 yds white spandex - enough to wrap around your torso
(You may want to source some 'wet look' or metallic spandex - it's more opaque than regular spandex. Try SpandexWorld.com)
* 1 yd turquoise spandex
* ...and matching thread
* some scraps of lightweight interfacing (NOT iron on), wide enough to go across your chest.
* a sewing machine with a stretch stitch
(preferably not zig zag - a stretch stitch is a stitch that goes forwards and backwards so that the stitch has give but is still sews a thin straight line. My Kenmore converts to stretch stitch if you set the stitch length slider backwards - check your manual)
* stretch ballpoint needles
(Using the right needle for the right fabric is important - the ballpoint keeps the fabric from snagging and helps maintain correct tension)
* Washable marker
(I like using washable Crayola markers but you can also use a sewing pen)
* Iron & ironing board
Take measurements around your bust, waist, hips, and from clavicle to mid-hip. Make sure you are wearing the same kind of undergarments you'll be wearing when you're in costume (especially a bra). Using these measurements, take two pieces of white spandex and sew a basic, curvy tube.
Remember to sew it with the stretch stitch and stretch knit needle. Leave the top and bottom unfinished, we'll get to that later.
With it still inside out, try it on and check the fit. If needs to be tightened anywhere, you can mark those places with your handy marker while it's on your body.
...then take it off and sew it tighter where you've marked. You should now have a perfect fitting tube top!
Now cut the asymetrical "V" shape out of the interfacing. You will use this as a pattern for the spandex, and also to stiffen the fabric so it will hold the pointed shape.
Hold it up to your body to make sure it looks the way you want, and make sure it is as wide as the front of your tube top. FYI Jessica's V peaks on her left side.
Figure out how wide you want the turquoise part to be - my stripe is about 2.25" thick and I think that feels right but you might need to adjust for your proportions.
Using the interfacing as a pattern, cut two pieces of turquoise spandex, leaving an extra 1/2 inch on all sides for seam allowance. Then measure the back of your spandex tube, and cut a rectangle that is as wide as the tube, plus 1", and 3.25" high (or as tall as yours is plus 1" seam allowances). Sew these four pieces together: sew each back piece to each front piece first, making two turquoise circles. Then pin the two tubes right sides together, sew together across the top and turn inside out, to form the top of the costume.
...it should look something like this except maybe less derpy.
Iron down all the seams on LOW HEAT - spandex melts VERY easily be careful. You may even want to put a piece of fabric in between your iron and the spandex to keep it cooler, test it on a scrap of fabric before you do your sewn costume.
Slip the interfacing into the front piece but don't sew it in - the interfacing helps hold the shape of the point but it isn't stretchy, so it's better if it moves freely inside the spandex.
Pin the turquoise piece to the white piece so that the bottom edge lines up to the line you drew earlier. This is going to be a little awkward because the shape is now inverted, but if you pin the vertex of the V first and then the sides it should work out.
The fold in the turquoise piece should now be pinned so that it is pointed down on the costume. Switch to turquoise thread and sew 1/2 inch from the unfinished edge of the turquoise piece. Push the interfacing in so you don't catch it with your needle, and sew all the way around the tube.
Turn the turquoise piece up so that the fold is pointing up. Cut away the excess white fabric, rinse away the marker lines, and then iron the seam down (again, LOW HEAT).
And you're done!
For Jewel's costume I originally made it as all one piece, but the combination of the straplessness and the attached feet meant that every step pulled the whole costume down (eek), so I switched it to a shirt with matching pants and separate shoes. Not accurate but much more practical.
This is why I left the bottom unfinished, so it wouldn't make such a big bump when I tucked it into my pants. No worries, spandex won't fray.
Her belt is the remainder the turquoise spandex, sewn into a simple loop.
Her 'jewel' is two diamond pieces craft foam, one slightly smaller than the other. They are papier mache'd together and then sprayed with several layers of Plasti-Dip for smoothness, and finished with Testors Spray Enamel in Electric Pink. It's attached to the belt with a loop of velcro.
I made her earrings using some pink chandelier beads wired onto basic earring findings from Michaels.
And I used these gloves in Marine Blue, which were a close match for the turquoise spandex I got from Joann Fabrics.
Hope that answers all your questions, brilliant-but-scary-bad-wolf! Sorry it took so long!