Re: Why can't I grow crystals with confectioners sugar and brown sugar?

The rate or ability to grow crystals is dependant on the rates of two 
types of processes: the diffusion of the sucrose (sugar) molecule through 
the layer of syrup surrounding the crystal, and the positioning of the 
sucrose molecules in the proper position to form the crystal.
For your specific question I will anwser it in two parts.  For the first 
part you have to know what brown sugar is.  Brown sugar is white sugar 
surrounded or coated with molasses.  In the sugar refining world molasses 
is called an impurity which just means anything that is not considered 
sugar.  All impurities tend to impede the crystallization rate of sugar.  
Therefore it would be difficult or impossible to crystalize brown sugar.
The second part is slightly more difficult to understand.  Confectioners 
sugar is sucrose that has been very finely ground, meaning that their 
crystals are still there but very small.  Therefore I believe that you are 
getting crystalization with confectioners sugar but it is much to small 
for you to notice.  While with granular sugar you do get crystalization 
that you can see or notice.  Or it could also be the fact that the 
crystals are so small they have trouble lining up (explained earlier) to 
form a correct large crystal structure.