While DiamondCRETE makes a waterproofing substance, I’ve never used it, so I can’t say how well it works.
I can say, however, that I have used Ducksback Waterproofer by Masterchem and love it. It’s available at any home improvement center or hardware store. It is a water-based product specifically for heavy duty concrete and masonry. It penetrates the stone, it doesn’t turn yellow, and it works. When brushing it on your stone, try not to get too much on the glass. And just be sure to wipe the glass immediately after getting it on there. It doesn’t really hurt it, but it makes it a little filmy and then you’ll have to scrub it off later. Catch it early and save yourself some work. Your brushes will clean up with soap and water.
Treat your stepping stones to this waterproofing once a year.
