To give the interior associations with the aristocratic style of the Middle Ages, decor masters have long used brass, and especially often bronze. Casting from these alloys even now makes it possible to create monumental masterpieces that can decorate any home.
In artistic casting, alloys are more often used than pure metal. Bronze is especially popular - an alloy of copper with tin (additive and alloying element) in various proportions. If zinc is added instead of tin, the result is brass, and if nickel is added, cupronickel. Copper combined with aluminium, beryllium or silicon is also considered bronze. The alloying element is indicated in the designation:
- BrO5, where tin is 5%;
- BrOS5-25: 5% tin and 25% lead.
What are the technological properties of bronze? Casting is possible when the material reaches fluidity. The temperature at which copper melts is 1083°C. When tin is added to it, the threshold drops to 800 °C, which greatly facilitates the process of heating the raw material. After hardening, the product has a shrinkage of up to 1%. Depending on the components, bronze products will differ inhardness. With a minimum amount of tin, they can be forged, with a concentration of 20% or more, they become hard and brittle. Plasticity is added by the introduction of lead into the composition. The addition of zinc makes the material more resistant to corrosion.
The melting of metals is preceded by considerable preparatory work. One part of it is related to the manufacture of the model. At this stage, the sculptor sculpts a model to scale from plastic material. Then he translates it to life size in plaster or clay. A back impression is taken of this transitional model. A complex form has several constituent elements and is assembled in parts. Heated wax is poured into it. Wrapping the form, achieve its uniform distribution over the entire surface. After cooling, a model of the future sculpture is formed, made in wax. The author finalizes the details, corrects the shortcomings.
Artistic casting of bronze and brass is overwhelmingly carried out using such lost-wax molds ("wastes"). The sculpture is hollow with a wall thickness of 2-5 mm. Otherwise, if the metal filled the entire mold, then a massive casting would be too heavy, and a lot of material would be required. And it's not just the cost. When pouring, it would be necessary to immediately melt all of its amount, and this automatically increases the size of the hearth and furnace, complicates the process of supplying the alloy to the mold. In addition, shrinkage of the material will give inevitable deformation, which will lead to distortion of shapes and individualcomposition details.
After creating the wax form, the next step begins. The caster takes over. He creates his own mold for pouring molten metal. Wax is covered with a special heat-resistant composition in several layers. First, such liquid ceramics are poured into the wax mold. At this stage, a core is created - a “doodle”. After it hardens with the same composition, the model is carefully covered from the outside, setting the required number of "letniks" where the bronze will be sent.
Casting becomes possible after sintering (calcining) the mass at high temperature. As a result of this process, a strong ceramic shell is formed. The wax is evaporated through the vents and air outlets. The result is a hollow shape. After pouring metal, it breaks. The inner ceramic layer can be left or also removed through the access hole.
Casting bronze at home
It is also possible to obtain an alloy item in an earthen form. At home, if you have a template, you can make a bronze casting in this way. But you need to be prepared for the fact that it will not be possible to achieve exact copying of small details and refinement is to be done. The form is disposable, but the earth itself (a mixture of clay and sand) can be used repeatedly. Usually make detachable forms, consisting of two parts. But you can also make one-piece if you use a wax model. After sintering, the clay mold is boiled inwater, wax floats to its surface through the letnik.
Quality casting can be obtained if the mold is preheated. Copper and tin are heated in a steel crucible. Use a coal hearth or muffle furnaces. After complete melting, the metal is kept at a high temperature for several more minutes and poured into the let in a thin continuous stream. The product after cooling is additionally processed. First, the metal frozen in the letniki is cut off. Places are being cleared. Fine details are formed during the minting process. The product is ground, polished, if necessary covered with a patina.