Addendum

If you're wondering what kind of circle of mages would develop such a thing, probably one with access to the internet, to wit, time-travelers. Whether they're traveling forward or backward is beyond me to say.

Practicality vs. Theatricality

I'm not sure a form of magic that involves tinting glass with spells that explode when activated is financially responsible, but the 5-minute animated shorts will be tremendous.

The Fable of the Magic Jar

Once upon a time, a peasant came back from an adventure with a magic jar. He poured water in it, closed the lid, shook it, and opened the lid to pour out ice. He showed it to the villagers and turned their grain into bread, their beer into good beer, and their sand into glass. He showed it to the merchants and turned their ore into ingots and their dross into gems. He showed it to the king and turned his gold into a magnificent crown that the other monarchs soon would envy.
"Well then, why don't we crack it open and see how it works?" A suggestion from a king is nothing less than an order, and so the peasant smashed his magic jar on the palace's tiled floor. Among the shards, there was a tiny little wizard who instantly grew back to his full size.
"Thanks for getting me out of there, fellas!" the wizard exclaimed. "I accidentally trapped myself in there when I made it. Now I can show your magicians how to make jars just like mine." He did just that and ensured the prosperity of the kingdom forever.
Moral: If something's good, break it and see how it works; otherwise, how will you know?
Finis

Difficult Moral Questions

The hero and his wary companions crouched down to pass through the portal, half-blocked by a half-fallen column. The space within, once a chamber of a tall and sprawling palace but now more appropriately called a den.
"What kind of sage lives here?" the warrior wondered.
"This kind!" The dust itself seemed to lift from the floor's cracked tiles and became a mist. Out of it walked a man, robed and menacing in his dark power. "I am the sage you seek. The last sage of evil in all the world. And the wisdom you are to hear from me is to be careful of your actions and how far you go. There is a balance in this world, a balance of good and evil. You must not wipe out evil from the world!"
The hero gasped. "Why?"
"Because I would get lonely. There are hardly any evil people around as it is. Imagine if nobody else used swords. Nobody would understand why you think better swords are a big deal. Shops would stop selling them!"
"That does sound bad for you, but I think the world as a whole will get by," the healer mused.
"And, on top of that, can't you just get a hobby?" the lovable rogue asked. "Like gardening or polo. People are doing a lot with astronomy these days, right? You can have interests other than just being evil. That actually sounds pretty boring. Do you really talk about how evil you are with other people?"
The sage of terror examined his nails. "I used to, but you killed most of them. Not that they didn't deserve it, but you know how it is. Besides, I have no need for advice from you. I'm a sage. Obviously I already attended several meetings of a society of percussion enthusiasts, but I had to stop. I feared I was becoming less evil."
"Isn't that good? To be good?" the healer asked.
"No, because of the balance."

And when all the evil power was destroyed and the recreational glassblowing scene grew so big that it was all the last evil sage could do to keep up with it, leaving him no time for evil, the world did just fine. Better than ever, as it happened.
Finis

Addendum

You've got your working class sand mages who make glass all day, corporate sand mages who develop new glass-making techniques and run off with their secretaries, and starving sand mages who are confident their lack of productivity is truer to the spirit of sand.

Unusual Uses for Sand Magic

Making glass. Wait, no. That's probably the most common use for it.