Bronze Casting


Renaissance bronze casting processes

(MameiSun? ) -- See MameisNotebook for her Word document (attached at bottom of page) with some comments from mrc.
(JaymievieveAng? ) -- See JaymiesNotebook for her Word document & some comments from mrc.

Around 1500, founders developed the technology for replicating compositions. The first great entrepreneurs in casting and exquisitely patinating statuettes were the Flemish-born Mannerist Giovanni Bologna—known as Giambologna—and his assistants in Florence in the second half of the sixteenth century.
From What was this replication technique and how did it work? Learn more about Giambologna...

Another interesting quotation (

This sculpture was highly ornate, and due to the amount of detailing in the draping required a deviation from standard bronze techniques. To combat these problems Donatello developed a unique technique for casting bronze sculptures: first sculpting the figure in clay, then draping clay soaked cloth around the sculpture, allowing the clay to dry, and then making a mold from the results. It was in this manner that Donatello achieved the flowing grace of draping cloth, smooth lines, and polished surface, in his bronze works. Later artists would employ this same technique. During this time in his career Donatello partnered with a sculpture named Michelozzo. Together the two produced a sculpture dedicated to pope John XXIII; the relief of the Assumption of the Virgin on the Brancacci tomb in Sant'Angelo a Nilo, Naples; and the reliefs of theoutdoor pulpit of Prato Cathedral. As his style diverged from that of Brunelleschi their friendship fell in disrepair and was never fully reconciled.
-- worth learning more about.

Process issues & problems

(MeghanKennedy? ) -- See MegsNotebook#MeghanBronzeCasting for Meg's notes to go with poster.

Issues and problems associated with bronze casting in the Renaissance (and in general)

  • Shrinkage and its effects
  • Why can't you just add more bronze top "top up" a partly-filled mold after the first pour has hardened?
  • Gasses, porosity, etc. (what is porosity? Why is it undesirable?)
  • Why was cast bronze a particularly good choice for making a bell?

The attached powerpoint slides at the bottom of this page are taken from a lecture by Prof. Gutkowski at MIT for a manufacturing course. I’ve extracted the ones that talk in a non-technical way about what happens and that suggest some design solutions to minize problems with shrinkage.

Who and How

(RaynaWiles? ) -- See RaynasNotebook (bottom of page) for Word document final writeup & a few comments -mrc.

  • Which artists did which pieces? How did they do it? Did they use particular foundry facilities -- and if so, whose?

You can get some sense of this by reading the poster that is next to the large bronze bell in the 2nd floor of the Museo di San Marco which desribes a bell by (? Donatello?) that was cast by a local foundary that a number of artists used. The bell has a problem in that they evidently slightly miscalculated the amount of bronze so that the rings at the top are incomplete and there is a jerry-rigged contrivance to clamp onto the "stubs" at the top of the bell.

Il Rinascimento italiano segna, nel settore delle fusioni in bronzo e dei gioielli, un momento alto e forse mai più superato: Lorenzo Ghiberti, Donatello, Antonio del Pollaiolo, Andrea del Verrocchio, Bartolomeo Cennini e Benvenuto Cellini, sono solo alcuni dei nomi che hanno contribuito ad una produzione molto raffinata e dagli esiti estetici di assoluta eccellenza.

Weathering and Restoration

(AliceWarnecke? ) -- See AlicesNotebook#AliceBronzeRestoration for more notes and MS Word document writeup.

  • What happens to bronze with time? With pollution?
    • Various oxidation modes (patina) and other effects -- see also the links above for hydrogen embrittlement (under "problems") as a function of aging and corrosion.
  • How do we protect statues?
  • How do we restore damaged statues?

Other references and links

Da Vinci's Horse

Process Links

  • notes on making a modern monument with some discussion about how a large piece was cut into sections, cast, joined, etc. Also some general points about shrinkage, etc.

  • Shrinkage and how it creates defects in parts - nice short description in this trade article (see PDF attached below):
A thin section will complete its solidification first. As it solidifies, it begins to shrink and draws metal to refill this shrinkage from the larger section adjoining it. The thin section draws metal until it solidifies. The thick section is the last to solidify. However, as it solidifies it is looking for somewhere from which to refill its metal. Since the thin section adjoining it has already solidified, the thick section has nowhere to draw from and a shrinkage defect (an area of lesser density level often referred to as porosity) will develop on the exterior or interior of the casting.
From G. Smith and A. Spada, "Thick and Thin, Designing Copper Base Sand Castings," Engineered Casting Solutions, Winter 2003. For a bit more on how this happens, see the powerpoint slides attached below.

-- MarkCutkosky - 17 May 2005

  • large bronze bell :

  • Casting.ppt: longer version of casting presentation from MIT
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