Has anyone tried adding a few drops of glycerin to royal icing for a high gloss shine? If so, did it set up the same? How much did you add to what amount of icing?
Glycerine does not make royal icing shiny it stops it setting so hard and makes it easier to cut. The only way I've found to get royal to shine is to dry it very quickly. I usually put my royal icing run outs under a reading lamp whch does give a nice shine.
You may be getting confused with fondant. A few drops of glycerine mixed with water and brushed on does make fondant shine but it didn't work with royal when I tried it.