Dunno if I'm the first to think of this; a thin layer of cement on any surface and then just scribe in/through it??? should work.
cement tags reply If you had the right tools and a good perspective I think it would work. It cant be to thin because it will chip to easy but no it to thick because then it will take to long. About 1/2 inch would work
Purchased colorful industrial crayons off the net, 3/8 size i think.they write great in cement. Write on cement, smearing cement turds on a wall is absurd.