I grew up in West Baltimore and my friends and I played skully, especailly during the summer, almost everyday. This was during the 70s. We used for caps the tops from the plastic gallon milk jugs and the tops from certain liquor bottles, which we mainly found in alleys. The tops were made out of a sturdy plastic, which allowed us to melt the crayons and candles wax right into the caps. Also during heat waves, we would dig up asphalt from the streets and rooftops to fill in the caps.