Supplies:

Soda ash or washing soda
Fibre reactive dye
Non-iodized salt (kosher, sea salt or pickling salt)
Cotton T-shirt (pre-washed with detergent)
Rubber gloves 

Directions:
1. Add salt and washing soda 
2. Add dye to the water
3. Add the T-shirt from the bottom
4. Add more water to achieve a gradient effect
5. Move the shirt around to achieve an even colour

Check out Masha Apparel on Etsy.