I got an old t-shirt to experiment with burning lettering (not the fire extinguisher as a precaution!)
The old t-shirt I used was 100% cotton. I used a torch lighter to control the burning and avoid any injuries. Some of the fabric curled, so there would need to be an underlay of a different coloured fabric to make it stand out, perhaps even stitching around the burnt letters as shown in the sketch below.
It was actually really difficult to control the way the fabric burnt. I had to cut the letters into the t-shirt. In the end, I couldn’t get the lettering style I wanted. In my next experiment with the burning technique, I will cut the lettering out of cloth in the typeface of my choice and then singe the edges. I could also stitch around the letters to make them stand out more.