Sheet metal cones are usually hollowed before the seams are formed, by working along the curves forming the top and bottom parts of the pattern, and then in to the centre, with a block hammer used on a beech block with holes cut in the end of a depth suitable to the curve of the work. If the cones are to be of galvanised iron, the zinc scales would continually peel off the iron during the hollowing operation, so it would be advisable first to make the cones of black iron, and then to have them galvanised.