[mehrkat]

The techniques are state secrets. I'm reminded of the optics among the (forgive me I think it was the dutch but I can't remember for sure). The techniques to purify glass to make clear lenses were impossible to develop for a while in surrounding countries.

Just make the purifying process or the ability to smelt at that heat a state secret. It wouldn't hold forever but it would get you through several generations of experimentation and it would mean in a multi-generational game world it might matter but wouldn't until then.