Now that I read it again, the comment was about storing the master password in a safe, in which case, you could stamp it into a metal plate or some other solid that has a high enough melting point. Steel seems like a good choice of melting temperature, with titanium even better. Or try tungsten, for a much higher melting point.

My neighborhood burned up a couple years ago, and safes were fairly worthless, fire-rated or not. Papers were ash, precious metals were all melted. Many safes had shattered, or were so degraded they could be broken with a kick. Just a warning... I'm sure some safes can withstand intense housefires, but it seems like most claiming so, can't.