1. Buy your supplies.
Track down your supplies at a standard hardware store. You'll need the following: fabric dye, hot water, salt, rubber gloves, a large bucket (or something large to dye in), and mixing sticks.
2. Pin your curtains where you want the lines.
If you want an ombre effect, look at the curtain panel overall and choose where you want the color gradation to occur. Then put safety pins in those areas. This way you can see where your lines need to be, but the safety pins won't interfere with the dye.
3. Prep the dye.
It's as easy as hot water + salt + dye. Fill your vessel with hot water, about 2 gallons for 1 pound of fabric. The fabric dye may list a certain temperature (Rit Dye, which I used, typically says 140 degrees), so you may want to heat water with a tea kettle or in the microwave. Add 1 cup of salt to hot water and stir.
Once the salt is dissolved, pour in 1/2 cup of liquid dye.
4. Dunk + rinse
To achieve a light color, the initial dye bath is very fast. Completely submerge the fabric, then remove and rinse in cool water.
5. Do the second round of dye.
I used a royal blue dye for the initial dye bath, then added 1/2 cup of navy blue dye to achieve the two darker colors. Depending upon the color variation you want, this step may not be necessary, and you would just submerge the portions of fabric for different lengths of time.
6. Hold down partial curtain as needed to achieve darker color.
Submerge your curtain panels as far as the safety pins indicate, making sure to keep the panels even in the dye bath. Use your mixing stick to move the fabric back and forth in the dye bath. This step may take anywhere from 5 to 10 minutes depending upon the level of saturation you want to achieve.
Once the middle color looks saturated enough, lift the curtain panels out further to your second line indicated by safety pins. Move fabric around using mixing stick, again leaving it in the dye bath for several minutes until the color you want has been achieved.
Rinse the fabric in cool water, making sure to keep the lighter portions of fabric at the top so dye runs down to the darker ends. Be sure to rinse thoroughly until the water runs clear.
8. Wash and dry.
Wash in warm water with detergent. Follow care instructions on the curtain panels (mine you could put in the dryer but just check to be sure.)
And finally, you're ready to hang your beautiful curtains up!