If there's Boron in the cardboard first, though. Elements are entities which exist by themselves and cannot be made - there's the Periodic Table which lists all the elements. A copy of that would tell you what chemicals must exist first before they can be used. You read statements like 'Silverbeet contains Iron' - it might, if the ground it is grown on contains it first. And Boron is a form of Borax (or the other way around) you can buy it at the supermerket in the cleaning section. It is quite toxic when ingested and used in only tiny quantities for plants.