I have used tea to dye fabric and had successful results using PFD Kona cotton. The fabric took the tea evenly and turned out a soft old-fabric color. I got exactly the look that I wanted.
I tried this another time, and I ended up with a disaster. I had washed the fabric first to remove the sizing, but the tea didn't take evenly. It was a yucky blotched mess. I saved the fabric by running it through a bleach cycle, so it wasn't ruined. This mess made me realize I needed more information about dying fabric before I tried it again.
I checked out a library book on dying fabric. What I got from reading it was that successful dying depends on how you prepare the fabric before adding tea or any natural dye. I didn't want to mess with the chemicals.
Now, when I want a lovely old looking fabric, I buy PFD Kona and set the tea dye using the hot iron method.
By the way, I asked my quilt shop what PDF stood for, Prepared For Dye. LOL..