Ortesine (ORR-teh-zine)
Discovered in 125 AS by prospectors searching for valuable ores, ortesine is a pale green, chalky mineral that comes from the Draver Mountains. Brought home by one of the prospecters for his wife, a potter, it was first put into use in ceramics as a colorant. It took almost no time at all for the potters to realize that adding ortesine to their wares made them twenty times stronger and resistant to chipping and breaking.
Soon, there was a brisk business in mining and selling the mineral. As knowledge of its usefulness spread, pale green ceramics began springing up in marketplaces and homes across Polira. Ortesian porcelain became incredibly popular, as it lasted longer than other clay or ceramic wares.
But ortesine had more secrets to reveal. One market day in Vercour, a newly awakened caster was startled while shopping for dishes. She instinctively lashed out with magic, and the ceramics at the stall absorbed it all, negating the spell. The locals were astonished, the woman included, and the tale spread. Casters tested the limits, throwing magic at pitchers and sculptures, only to see it absorbed without a trace.
When King Gaetan was preparing what would be later known as the Sanguine Tower, he commissioned several ceramic makers to produce huge quantities of ortesian porcelain tiles, to line the interior of the keep. The tough ceramic is often put to the test there, and yet has only had to be replaced twice.
Other applications for ortesine were found. The Blood Guard, charged with guarding the kingdom's casters, experimented with different methods of utilizing it, until one ceramics worker found a way to make a buckler-type shield out of thick ortesian ceramic. The process was lengthy and involved, but provided excellent protection against magic. These ortesian shields became standard issue and continue to be so today.
No one knows how ortesine is formed. There is no mention of such a substance in the few surviving documents from the Age of Magic. It is possible that the mineral simply lay undiscovered for some time. However, given how pervasive it is within the Dravers, some have theorized that it was created during the Shattering, itself. That region was known for magic storms and rifts long after the Shattering subsided, and it is possible that the interaction of the physical plane and the mystic plane created an anti-magic substance somehow.
by Nightflyer0ne via Midjourney
I like how diverse your material is and I think it's great that you've integrated the culture into the article. However, I would have liked a few quotes from a magician, for example, and more brief key facts to give the article more credibility.