I experimented with a lot of fabric markers because I wanted to make sure the writing would stand the test of time. I went with Pentel Gel Roller for Fabric, black ink, 1.0 mm. I used white PFD (Prepared for Dyeing) 100% cotton fabric for the center square and preshrunk it. I ironed freezer paper to the back of each block to make writing on the block easier and it really was the best way to go. I made a large sample block to sit on the table so guest could experiment before writing on the blocks. I made sure to have plenty of markers on the table and some in reserve because I didn't want to run out of ink!