# Lost-Wax Bronze Casting: answers and explanations

Testmigo Practice Test 3, Listening Part 4

Source: Written by Testmigo.

## Answer key

| Q | Answer | Proof |
| --- | --- | --- |
| 31 | resin | resin taken from a particular tree |
| 32 | air | the air that the metal pushes ahead of it has a way out |
| 33 | bubbles | If any bubbles get caught against the wax |
| 34 | water | runs into a container of water |
| 35 | chemicals | Chemicals are applied to the metal |
| 36 | zinc | isn't tin at all, but zinc |
| 37 | currency | those rings served as currency |
| 38 | solid | Chola figures were cast solid |
| 39 | streets | paraded through the streets |
| 40 | implants | biomedical implants |

## Why these answers are right

**31. resin.** Describing the wax used in South Indian workshops, the lecturer says beeswax is blended with resin taken from a particular tree, plus a little groundnut oil. The flow-chart already prints the oil, and obtained from trees paraphrases taken from a particular tree.

**32. air.** Once the wax is gone, the rods leave channels; molten bronze flows in through them, and the air that the metal pushes ahead of it has a way out. During the pour matches the moment the bronze flows in, and escape paraphrases has a way out.

**33. bubbles.** The first layer of investment is the finest and is put on with great care, because if any bubbles get caught against the wax, each one shows up as a blemish on the finished metal. Without leaving any paraphrases the warning about bubbles getting caught.

The why and the trap for questions 34 onwards are free with an account on the [answers page](https://testmigo.com/ielts/listening/lost-wax-bronze-casting/answers).

## Transcript

**Announcer:** Part 4. You will hear a lecture about lost-wax casting, a way of making sculpture in bronze.

**Announcer:** First, you have some time to look at questions 31 to 40.

**Announcer:** Now listen carefully and answer questions 31 to 40.

**Lecturer:** Good morning. Today's topic is a technique that's been used to make metal sculpture for thousands of years, and that foundries still use now: lost-wax casting.

**Lecturer:** The name says it all: the sculpture begins in wax, and at some point that wax vanishes and molten metal takes its place.

**Lecturer:** So, step by step. It starts with a wax model, because wax can be carved, warmed and joined, and it holds very fine detail.

**Lecturer:** It isn't always pure beeswax, though. In the South Indian workshops I'll come back to later, craftsmen blend beeswax with resin taken from a particular tree, plus a little groundnut oil.

**Lecturer:** Then the caster fixes wax rods to the model, branching out like a small tree. These are called sprues.

**Lecturer:** When the wax has gone, the rods leave channels behind. Molten bronze flows in through them, and just as importantly, the air that the metal pushes ahead of it has a way out.

**Lecturer:** Next, the whole thing is encased in investment, which is just the casting term for the mould material. It goes on in several layers.

**Lecturer:** The first layer is the finest, and it's put on with great care. If any bubbles get caught against the wax, every one of them will show up as a blemish on the finished metal.

**Lecturer:** When the outer layers are dry, the mould is heated. The wax melts and pours out through the channels, and that's where the word lost comes from.

**Lecturer:** Although it isn't necessarily wasted. You might assume it just burns off, but in traditional workshops the melted wax runs into a container of water, and then it's cleaned and used again.

**Lecturer:** Before the pour, the empty mould is heated until it's red hot, which stops the metal cooling too suddenly and spoiling the surface.

**Lecturer:** Then the bronze goes in, at well over a thousand degrees Celsius, and the mould is left to cool. With a large piece, that can take a day or longer.

**Lecturer:** After that, the mould is broken open to free the casting, which means, of course, that it can only ever be used once.

**Lecturer:** What comes out is rough. The sprues are now bronze rods, so they're cut off, and the surface is filed and chiselled until the marks of the process have gone. Foundries call this chasing.

**Lecturer:** The final stage gives the sculpture its colour. It can look rather like paint, but it isn't. Chemicals are applied to the metal and react with it to form a thin coloured layer, the patina, which is then polished.

**Lecturer:** Now, what exactly is bronze? It's an alloy, mainly copper, with tin added. But there's a limit: once the tin goes above about eleven per cent, the metal becomes too brittle for most practical uses.

**Lecturer:** And not everything we call bronze really is. Take the famous Benin Bronzes, made by the Edo people of what is now Nigeria, mostly between the sixteenth and nineteenth centuries.

**Lecturer:** Most of them are in fact brass. In brass, the metal that's combined with copper isn't tin at all, but zinc.

**Lecturer:** Where did the metal come from? European ships brought brass rings called manillas, and in Benin those rings served as currency.

**Lecturer:** A study published in 2023 compared their chemistry with Benin pieces and traced the metal mainly to the Rhineland, in Germany.

**Lecturer:** Moving to South India, the Chola period, roughly the ninth to the thirteenth centuries, produced some of the most celebrated bronzes in Indian art.

**Lecturer:** Large Greek statues were usually hollow, but Chola figures were cast solid, and since each mould was destroyed, every one is unique.

**Lecturer:** They weren't made to stay in one place. A figure was kept in the temple treasury, and on a festival day it was bathed, dressed and paraded through the streets.

**Lecturer:** The tradition hasn't died out. In the town of Swamimalai, in Tamil Nadu, craftsmen still cast religious figures by this method.

**Lecturer:** The Riace bronzes, by contrast, are Greek, from the fifth century BC. These two figures, nearly two metres tall, were spotted by a diver off southern Italy in 1972.

**Lecturer:** They're hollow, cast around a core, and the details are remarkable: the lips are copper, and one still has silver teeth.

**Lecturer:** Finally, how is it done today? An art foundry usually takes a flexible rubber mould from the artist's original, so it can make several wax copies.

**Lecturer:** And instead of the traditional clay layers, the wax is dipped in a liquid containing silica and then coated in a sand-like grit, over and over, until it's sealed inside a hard shell.

**Lecturer:** Industry uses a refined version of the same idea, known as investment casting, to make things like gas turbine blades and biomedical implants.

**Lecturer:** So an ancient craft is still part of modern engineering. Next week, we'll turn to iron.

**Announcer:** That is the end of Part 4. You now have 30 seconds to check your answers.

[Practice Lost-Wax Bronze Casting](https://testmigo.com/ielts/listening/lost-wax-bronze-casting)