Nepi, we are going somewhere!!!!, I really like the design that you made on the top of that cone.
The correct mixture for plaster: Two plaster to one and one half water: 2 gallons plaster + 1 1/2 gallon water, mix quickly and pour quickly as well, it will start to harden within a few minutes.
Your next assignment : an extra large traffic cone 
One 25lb bag of plaster, that should be about 4 gallons (plus or minus a little)
3 Gallons of water
Heavy on the sand (about 6 or seven cups), less if you like
A bunch of any stones that you like (3 or more hand full), less if you like
Some larger crystals, 5 like in a HHG
Pour the thing in 2 batches, 3 if it is toooo hard to stir, just pout the next batch on the top of the last
Dont forget to tape shut the end of the traffic cone 
OK ….you have 10 minutes to completion…………….we are waiting for the picture……………………. 
josh