Some info for you.
While this may be an issue for ordinary chalk, it is NOT an issue with a Kamui block.
They are made from a completely synthetic compound. Each particle is the same size and weight. It was devised specifically to achieve a consistency that was NOT present in other chalks.
This still does not answer the question of why someone would freeze chalk. Any talk about temperatures in Northern regions is conjecture. Kamui actually had complaints from people who noticed a change after they froze it.
Go figure!
the presence of bubbles are an indication that the chalk mixture was poured into a mold in a liquid form, unlike other brands of chalk that are pressed/formed as a somewhat dry mix.
there are inherent issues with this type of production process, the least of which is bubbles. there are more.
for example, there is also the issue of consistency from the 'top' of a cube to the 'bottom'. keeping various sized particles suspended in a liquid mix is very tricky to do, especially while the mix is drying or 'setting'. the heavier particles tend to settle, creating a denser cube at the bottom.
this can (partially) explain a particular cube appearing to 'change' over time, as you grind closer to the bottom.
While this may be an issue for ordinary chalk, it is NOT an issue with a Kamui block.
They are made from a completely synthetic compound. Each particle is the same size and weight. It was devised specifically to achieve a consistency that was NOT present in other chalks.
This still does not answer the question of why someone would freeze chalk. Any talk about temperatures in Northern regions is conjecture. Kamui actually had complaints from people who noticed a change after they froze it.
Go figure!