Lost wax technique

GARDECO

The lost wax techn que

Ca st ing b r on z e piece s

The or g nal p ece

The art st creates a model, generally n plaster, clay, or wood. Th s s called the or g nal p ece.

The Mold

Of the or g nal model, an exact negat ve s made n s l cone, a very f ne, elast c and shapeable mater al. The s l cone mold s then placed nto and supported by a r g d outer mold. Somet mes mult ple molds are needed to recreate the or g nal model, espec ally for large models. Thanks to the durable propert es of the s l cone, the mold can be used to cast up to a hundred p eces.

The Mold

The mold s made of two p eces that are put together. L qu d wax s poured nto t and sw shed around unt l an even coat ng of approx mately three m ll meters covers the nner surface of the mold. After the des red th ckness s reached, the excess wax s poured out and the mould s turned ups de down leav ng the wax layer to cool and harden. n a later stage, the bronze w ll replace the wax and have the same th ckness as the wax n the mold.

The wax model

The result s a hollow wax copy of the or g nal model. The wax s then ‘chased’ by hand, mean ng that mperfect ons are rubbed out w th a heated metal tool and m ss ng deta ls are added, such as the art st’s s gnature, the ed t on number and the foundry seal. The wax copy now looks exactly as the end product should look l ke.

A structure of wax channels, called sprues and gates, s attached to the wax model. The sprues prov de paths for the molten bronze to flow nto the mold evenly and for the wax and a r to escape the mold when the bronze s poured.

nvestment mold

The sprued wax copy s d pped nto a slurry of f nely granulated ceram c. Th s coat ng process s repeated unt l a th ck and course shell, or ‘ nvestment mold’, s formed. The nvestment mold s then dr ed and heated and the wax melts and runs out. Now all that rema ns of the or g nal model s a negat ve space formerly occup ed by the wax, ns de a hardened, f re-res stant ceram c shell.

Bronze s then melted and poured carefully nto the ceram c shell, f ll ng the space left by the ‘lost’ wax. The f lled shells are then left to cool. Once the shell s cooled down, t’s hammered away, releas ng the rough bronze cast ng. The bronze cast ng and ts sprues and gates are an exact reproduct on of the wax model.

Chas ng

The network of sprues and gates s cut off, the mater al to be reused n another cast ng. ust as the wax model was chased, the bronze cast ng s now f led down and pol shed unt l the s gns of the cast ng process are removed. The result s a cast ng that looks exactly l ke the or g nal model. As ment oned before, larger sculptures are generally cast n segments. The segments are now o ned together, a process that s called braz ng.

Pat nat on

The last step s the pat nat on process: hot or cold ox des are appl ed to the surface of the bronze to speed up the natural age ng process. Th s results n a colour change, such as green, blue and brown, that creates a un que f n sh to the metal. The pat na also prov des a protect ve coat ng for natural weather ng. The pat na w ll nev tably change over t me, th s s an ag ng process as a result of natural weather ng and enl vens and adds charm to the sculpture.