So here goes. I'll make it out of granite. Granite is rock formed by fire. It is very hard and extremely durable. Because it has been fused by fire it resists chipping and splitting.
Modern men use diamond saws and drills to form it.
But the fact, that it is hard, and resists cutting did not deter the ancients. They cut it with jeweled saws, drilled holes in it, and cut thousands of inscriptions in its facing. Granite weighs 170 pounds per cubic foot. Now, for the reconstructed float. If you can imagine, a bath tub cut from a block of granite, you have formed a clear basic picture of the float.