Talking about bells foundry, A.E.I. Perego can boast centuries of experience, thanks to the tight collaboration with Barigozzi Foundry in Milan. This one, founded in 1806 as Napoleonic Eugenia Foundry, has been an historical foundry of Milan, located in the Fontana area, near Santa Maria alla Fontana church, in the Isola district. A foundamental and not simple experience, being quite difficult to assembly and harmonize a bells concert. Nowdays, A.E.I. Di Perego has a large variety of own bells fusion moulds and, using 3D scanner, it is able to reproduce exactly the hystorical foundries' moulds, such as the one of Prunerio Foundry in Grosio and, of course, Barigozzi Foundry ones.
The note emitted from each bell depends on its shape, size and weight. The bigger and heavier the bell is, the deeper the sound will be.
Together with this basic note, the bell emits also an harmonic ensemble, that is vibrations of lower or higher frequency than the basic note. The harmonic ensemble is tied to the different diameters along the bell body and the basic note is the one produced at the maximum diameter level. The wider the harmonic extension and assonance are, the better the bell quality will be.
The bronze alloy, which bells are made of, is generally, composed of around four parts copper and one part tin. The tin has the characteristic of softening the acoustics, though it makes the alloy softner and therefore easier to be ruined by the mild iron-made clapper strikes. Therefore, a alloy composed of 22% tin and 78% copper is usually used.
Two moulds are used during the fusion process: one made of bricks and clay, very compact and hard called "male", representing the inside bell and the other, less hard and easily removable made of mixed clayish material and natural fibers, representing the outer shape of the bell. By a thin wax layer, the decorations and the inscriptions signs are attached on this outline called "false bell" which has the definitive shape of the future bell. The two moulds are then covered by another one made of clay and called "the shirt" - whose sides will be ended by the false bell complete with wax signs, decorations and friezes - to which the false bell must overlap perfectly.
Next step is the firing of the two overlapped clay moulders; this firing causes the melting of the thin wax layer used for the decorations, whose imprints remain perfectly impressed in the inner side of the "shirt" which represents the exact external look (in negative) of the new bell.
After the firing is completed, the "shirt" is taken away to allow the cleaning of the "male" removing the soft layer that had been applied, creating, in this way, the volume and the mould that will be filled with the poured bronze. After this delicate operation, the "shirt" will be re-attached to the "male" and put in the casting hole and the molten metal (casting temperature 1100° C) will be poured between the two moulds. After cooling down, sometimes cooling takes several days, the mould is opened and the bell, cleaned and smoothed, is ready to be admired.
Bells foundry and custing is a difficult and very delicate art and it is based, first of all, on a precise project represented, in brief, by the bell profile, on which the extension, the musical note, the tones and the pleasantness of the sound depend.