The higher classes seal their mail with wax seals. How could I make sure a design on the seal is uncopyable or at least make it very hard?
Magic exists, but it's primarily elemental manipulation. Signet rings can be made out of magic disrupting material to prevent arcane duplication with earth magic, but is there a way to prevent copying from the seal design?
Technology level: http://tvtropes.org/pmwiki/pmwiki.php/Main/SchizoTech Predominately "medieval" with higher technology with lightning powered railgun, but none that I think affects the question.
Edit for more details:
- For the sake of my story, it has to make duplication pointless or too difficult to be worth much.
- It should be relatively simple and achievable by the poorest of nobles, so it should not be too expensive.
- The wax seal is for the dual purpose of making sure the letter was secure in transit and possibly ensuring the legitimacy of the document.
- The original signet ring itself cannot be directly duplicated with magic so it has to be handcrafted. This leaves any unscrupulous people only the wax to work with.
- Magic wax is possible by imbuing energy.
- Everyone's magic has a signature. The closer by blood, the more similar. Twins have almost identical signatures. For example, a "barrier stone" activated for a descendant dozens of generations later but it's very general. A signet ring meant to be handed down would be slightly less general but it's the same idea.
Is that enough of a "criteria?"