This cylinder was made of a mixture of clay and sand, with the addition of hay and straw.

The space left between the mould and the masonry was to be filled with the molten metal, which would thus make the sides of the cannon six feet thick.
This cylinder, in order to have its equilibrium maintained, had to be consolidated with iron bands and fixed at intervals by means of cross-clamps fastened into the stone lining; after the casting these clamps would be lost in the block of metal, which would not be the worse for them.
This operation was completed on the 8th of July, and the casting was fixed for the 10th.
"The casting will be a fine ceremony," said J.T.Maston to his friend Barbicane.
"Undoubtedly," answered Barbicane, "but it will not be a public one!" "What! you will not open the doors of the inclosure to all comers ?" "Certainly not; the casting of the Columbiad is a delicate, not to say a dangerous, operation, and I prefer that it should be done with closed doors.

When the projectile is discharged you may have a public ceremony if you like, but till then, no!" The president was right; the operation might be attended with unforeseen danger, which a large concourse of spectators would prevent being averted.

It was necessary to preserve complete freedom of movement.

No one was admitted into the inclosure except a delegation of members of the Gun Club who made the voyage to Tampa Town.