I've not tried charred cloth, but I did try a new dry wick from a kerosene lantern once. Particularly once there was a blackened edge, it would glow and smoulder fairly easily after hitting it with the lens. But, frustratingly, the wick material would just turn to ash without actually bursting into flame.

I would think a piece of charcoal would be the same way, glow and smoke but no flame.

The painted newspaper burst into a bright healthy flame readily after hitting it with the lens, and I'm sure the dried paint helped keep it burning briskly. I had to blow it out several times to get it to stop burning entirely.