Find out more about crystal seeding from this Hampton Research paper.Check out the link on crystals formed by volcanoes Indianapolis Childrens Museum.This works whether you are talking about crystal growing kits, making liquid nitrogen ice-cream or gemstones! Simply put, the longer it takes to form a crystal, the larger the crystal will be. Over time, more and more of the sugar continued to settle out of the solution onto the kebab stick and so your crystals continued to grow!
This rough surface gives plenty of microscopic nucleation points for the molecules of sugar to settle. The sugar was more likely to settle on the kebab stick rather than the glass as the kebab stick has a rougher surface. As the water cooled down, less of the sugar crystals could remain in the water and so they began to settle out onto the kebab stick, which effectively acted as a seeding crystal. You made a super-saturated solution of sugar and water! The sugar crystals could only stay dissolved whilst the water was hot. Cooling the solution down made it super-saturated, which is unstable.
