Wet sandpaper cuts the crystal. Edge must be sanded each time at a slight angle to keep the rock active. This took approx 30 put togethers, test, take apart, grind, clean, put togethers etcetc. Don VE3LYX
I assume you are using very fine grit sandpaper, something like 250. Do you use a glass plate as the flat working surface?
I take it you mean hold the crystal at a slight angle from vertical and sand along the edge, lengthwise, not across (perpendicular).