What you'll need:
Jeans (or denim shorts)
Bottle of liquid Rit dye (I used violet)
Bucket (I used my trashcan)
Something circular (to trace for the scallops)
Paper for pattern making
Fray Check (here)
First things first, try on your jeans and mark where you want to cut them. I suggest marking long than you think you want them first and try them on again after cutting. I've cut too short the first time way too many times, so you live and you learn. Also make sure you leave a little extra length for the scalloping since it will take off a bit more of the length. (You can obviously skip this step if you are using shorts and not jeans.)
Once you've got your shorts the length you want them. Rinse them with water to prep them for dying.
Next your going to need to fill the bucket (or trashcan in my case) with 2 gallons of hot water (depending on how dark the denim is you are working with you might want a little less water. I used 1 and 3/4 gallons for my shorts.) Then add a 1/3 a cup of your dye to the bucket and mix well.
Now dip your wet shorts about half way into the dye (or however far up you want the lightest part of the ombre to start) and let them sit for about 10 minutes.
Remove the shorts and wring out excess dye. Add 1/3 a cup more dye to the bucket and mix. Dip your shorts back in the water about a third of the way down (or where ever you want the medium part of the ombre to start) and let them sit for 5 minutes or so.
Remove them once again and wring out the excess dye. Add the last 1/3 a cup of dye to the bucket and mix. Now dip just the very bottom of the shorts in the dye (or again where ever you want the darkest part of the ombre to begin.) I started this portion a little higher because I wanted to make sure I still had a good amount of the dark portion once I cut the scallops. Let sit for another 5 minutes or so.
Remove and rinse until the water runs clear. Then hang your shorts outside to dry in the sun. You could probably dry them in the dryer if you're in a hurry or it's not a pretty day, but I wouldn't suggest it as it will cause the bottom to fray and since you still need to cut the scallops you'll want as little fraying as possible.
Once your shorts have dried it's time to scallop them! So iron them flat if you feel you need to (I did) and then measure around the bottom of each leg of your shorts. Then you have to decide how big you want your scallops and divide that measurement by the size of each scallop to get the number of scallops you will have on each leg. I forgot to do this part and ended up realizing it when I got around to the end and there was a bit of a gap between the first and last scallop (which is why I'm probably not explain this part as well as I would if I had actually done it. o.O). I ended up making it work in the cutting process, but it could have gone really badly from there, so make sure you measure!
Then use something circular that fits the measurement you need and create a pattern to trace. I used the top of a spice jar to trace the scallops onto a piece of paper a few times in a row to create a pattern that I could pin to my shorts. Now that you have a pattern turn your shorts inside out and trace the pattern around the bottom of the shorts with a metallic pen. Then cut around the guide you've just drawn on.
Once you're done cutting your scallops, just follow the directions for the fray check to apply it all the way around the edges of the scallops. You're done! Rock them with pride!
The pair of jeans I thrifted for this were some serious straight-legged mom jeans... but the fit was good in the top and loose in the thighs, so I had faith they'd work out. And boy was I rewarded! Perfect high-waisted shorts glory! I'm so excited with how they turned out!