This might be a bit of a silly question. In reading Deuteronomy 27 I see a command to build an altar of whole stone and not use any iron tool on it, but then a little further on is a command to write the words of the law upon the stones. How did they write on the stones without using iron tools on them? Was there a different kind of tool? Were the words painted instead of engraved?

There are 2 sets of stone: 1. (mentioned in verses 2-4 and again in verse 8) which were plastered white and on which the words of the Torah were written (not chiseled), and the 2nd set is stones used to make an alter (verses 5- 7) where it explicitly states not to hew the stones.