An exact stone model of the outer bell, sometimes called a false bell, is built on a base-plate using porous materials such as coke, stone or brick. It is then covered first with sand or loam sometimes mixed with straw and horse manure. This is given a profile corresponding to the outside shape of the finished bell, and dried with gentle heat. The false bell is then covered with molten wax and figures and inscriptions, also made of wax, applied on top by hand. The false bell is painted over with three coats of fireproof clay and then enclosed by a steel mantle overcasing. The empty space between the false bell and the mantle is filled in with cement and left to harden before the mantle is lifted off. The false bell is chipped away from the inner core to leave just the wax and cement. Any leftover scraps of the false bell are removed with a blow torch. The mold is then set over a coke fire to melt the remaining wax and to evaporate any water that has accumulated.

A model of the inner bell is then constructed of stone and coated with fireproof cement. It is then smoothed to remove any irregularities

http://en.wikipedia.org/wiki/Bellfounding#Constructing_the_m...

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Note added at 21 mins (2015-01-12 11:03:40 GMT)
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Today, the core is covered with grease and a clay "false bell" is modeled over it. The false bell is greased, covered with more clay (the "cope"), and baked. When the false bell has cooled, the founders lift off the cope and remove the false bell. They then place the cope back over the core. - http://www.russianbells.com/founding/bellmaking.html

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Constructing the mold

3 An exact stone model of the outer bell, sometimes called a false bell, is covered first with sand or loam, then with molten wax. Figures and inscriptions, also made of wax, are applied by hand. The false bell is painted over with three coats of very fine, fireproof clay. It is then enclosed in a steel mantle that has been lowered by rope pulleys. - http://www.madehow.com/Volume-2/Bell.html

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A bell is cast in three stages: the core, the "false bell," and the mantle. - http://www.beiaard.org/enghistoriek.html

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The „false bell“ is formed on the dry clay core. - http://www.glocke.com/pdf/broschur_englisch.pdf - page 4