Take a glass rod and rub vigorously the wall of the flask, the substance will crystallize out of the solution.
Take a fire polished stirring rod and etch (scratch) the glass of your beaker. The small pieces of glass that are etched off of the beaker serve as nuclei for crystal formation
But reaching back to my halcyon years of organic synthesis and crystallization, recalling vivid memories of scratching the sides of Erlenmeyer flasks with a glass rod to induce crystallization
It's a common lab technique. But does it have a name?