First of all, let me say that you will need "bleeding" tissue paper. It is designed so that the colors bleed out of the paper. You can do an online search and find several places that sell it.
You will also need a fabric that will take the dye. I've done this technique with cross stitch fabric (which is what was used for this instructable) as well as 100% cotton and 100% silk scarves (my girl scouts loved that one!).
The last things you will need are an iron, a spray bottle, and something to put underneath the fabric (I usually use a trash bag).
I made this one at TechShop Austin (awesome place - I'd recommend going out and taking a tour if you have a chance). www.techshop.ws
Step 1: Spray the Fabric
Skip this step if you have a specific pattern that you want to create and don't want the tissue paper to start bleeding immediately (it will!).
This will help your fabric to lay flat (especially if it's cross stitch fabric that has been rolled up).
Step 2: Lay Out Tissue Paper
This is the easy step. Lay out the tissue paper in any pattern you want. I just rip it (the edges of the colors will bleed together anyway). This particular project was supposed to have a desert/sky feel. I layered brown and orange for the desert to get the desired color.
As expected, colors will bleed together. If you overlap blue and red, you'll get a purple color in the overlap.
I purposely made strips for the sky so that I had a wispy cloudy look. In the end, it was a little too light, so I added some darker blue (you can see this in Step 3).
Step 3: Spray the Tissue Paper
You want it very saturated. This is not only to release the dye, but to make sure the tissue paper is making good contact with the fabric. Otherwise, you'll get white (or original color) patches of fabric. This creates a cool tie-dye effect, but not necessarily the color you're going for.
Step 4: Remove Tissue Paper
Let it sit for about 10 minutes or so (longer if you want a bolder, darker color).
Then, remove the strips of tissue paper. If you have a lot of strips overlapping each other, you'll get large sections to come off at once.
Step 5: Iron Dry
Lastly, you'll want to use an iron to set the color and dry the fabric. It probably won't be completely dry, but no longer dripping wet.
Put a towel or paper towels down over your ironing board - the colors will bleed onto your ironing board cover.
Also, the colors will sometimes stick to your iron, so start where the colors are the lightest or else you might accidentally have dark color over your light colors.