The goal here is to create large, well formed sugar crystals that demonstrate the underlying crystal structure (monoclinic). Sugar crystals may at first appear to be cubical as with table salt. But upon closer inspection, they are a bit tilted. Magnify some sugar right out of the bag and you’ll see the same structure on a smaller scale.

You can start with as much as about 3 cups of sugar for this procedure. You’ll get more crystal, but it starts more quickly than I wanted. I’ve seen many internet sites call for only 2 cups, but I don’t think you’ll get too much from that. I chose 2.5 so that I would still get a good crystal but the process would start more gradually. My hypothesis is that the key to growing well-formed crystals is slow growth. Does it really matter? Only more experimenting will tell.

Try using different shapes for the weight or adding food coloring. We make a “crystal tree” each year using a ring stand with several rings as the structure.

An explanation I often see for the slow growth of sugar crystals implies that the cooled solution is saturated and crystallization takes place as water evaporates. That explanation makes no sense given that the volume barely changes, if at all. I found this page from the New Zealand Institute of Food Science and Technology to be quite enlightening. Who knew that sugar had a metastable region?

https://www.nzifst.org.nz/unitoperations/conteqseparation10.htm

Based upon my measurement of a cup of sugar to be about 230 g and an ambient temperature of 20 C, one should stay a bit under the 3 to 1 ratio. Maybe more like 2.7 to 1. You certainly want to avoid “spontaneous nucleation”. I’ve had students who put the jar into the freezer to cool it down more quickly. The result resembles slush. Very tiny crystals, presumably from quick and pervasive growth.