Normally when I build a prop, I use steel, or cover it with glue and iron dust, and then apply various oxidizing compounds, acids (and sometimes salts and bases) to make a real rust. Then, I gently wash it and seal, or not.
This is great for a photoshoot, because nothing can beat real rust in “look like rust” contest. Sadly, removing 100% of the chemicals is not possible and I end up with stuff that can irritate gentler skin.
How can I imitate rust on props for LARP or “accessorized RPG”, that would look rather real, but would be safe and non-allergic even with prolonged handling?