Here's a breakdown of why:

* Saturated Solution: A saturated solution holds the maximum amount of dissolved borax at a given temperature. This means there's plenty of borax available to crystallize.

* Slow Cooling: Rapid cooling can lead to smaller, less well-formed crystals. Slow cooling allows the borax molecules to arrange themselves in an orderly pattern as the solution cools, resulting in larger, more beautiful crystals.

* Hot Temperature: Borax is more soluble in hot water. Starting with a hot solution allows you to dissolve more borax, creating a highly saturated solution that will yield larger crystals as it cools.

Here are some general temperature guidelines:

* Start with boiling water: Dissolve the borax in boiling water (around 100°C or 212°F).

* Gradually cool: Allow the solution to cool slowly, ideally over several hours. You can place it in a warm area, or wrap it in a towel to slow down the cooling process.

* Ideal crystallizing temperature: The ideal temperature for crystal growth varies depending on the amount of borax used and the specific conditions. However, a range of 40-60°C (104-140°F) is often recommended.

Important note: The exact temperatures and cooling rates may need adjustments based on your specific setup and desired crystal size. Experimentation is encouraged!