Soluble Glutinous Rice Starch is used as a water-soluble binder in many of Takeo Shimizu’s formulas. This is not just because SGRS is more easily obtained in Japan than cornstarch derivatives like Dextrin. SGRS does indeed have superior binding characteristics than Dextrin.
There is no effect on color or burn time by replacing a like amount of Dextrin with SGRS, or vice-versa.
SGRS is well adapted for the toro method of rolling round stars, which was developed in Japan using this material. People often use Dextrin in the US and use an atomizer to spray the stars with water, while dusting with dry composition. Stars can be rolled effectively using both techniques. Star compositions made with SGRS have a property of drying in such a way that once dry, they do not easily soften when wet again. This property lends itself to the toro method. Dextrin-bound compositions do not behave this way and easily become soft and soggy when re-wet.
Another benefit of using SGRS for the toro method is that SGRS dissolved in water has a much higher viscosity than does a comparable solution of the ordinary yellow Dextrin. Toro made with SGRS thus holds the insoluble components of a composition in suspension better than they would be in a Dextrin-based slurry.
Dextrin is still the binder of choice for pumping/pressing.
The hardness of stars is not solely a property of the binder. For example, a silver star containing a lot of flake aluminum will not be as hard as a tremalon star made with atomized aluminum. Binders do contribute to the hardness of a star but it more tied to the composition that is being bound.