No problem with sharp tip - used a crayon sharpener. Used one with a piece on it that catches the shavings - am going to try to put them in flannel and try pouncing to get the pattern once I collect enough. I use that method with baby powder on my ceramics.
Didn't try colored chalks - figured the dye might leave a permanent mark. I've got some my grandkids use on the driveway. Will try on a scrap and let you know. Hopefully tonight.