Another key to drying tiles successfully is to keep flipping them over
from day to day. Or dry them on racks that let air get to the bottom.
Even drying is key. Sometimes on the first night of drying (wet) I put
a small kiln post in the corners of the tiles to keep them from lifting
up. Keep them covered overnight, the next day, leave the posts on the
corners, but put some holes in the top of the plastic. Next day, add
more holes. Flip them when they are barely leather hard, and keep
flipping them. I made a tile boardgame in college. I pressed alphabet
soup letters into the clay while damp to write on the tiles. (Yes, I
was OCD on that idea.) I'll never forget how beautiful the mold was all
over the letters when I uncovered my tiles. We all had a good laugh and
a gag on that sight. In the end, it didn't cause any harm.