ADVANCED MATERIALS & PROCESSES | MAY/JUNE 2024 30 Fig. 1 — Bronze cymbal, Central Anatolia, Hattian, 2300-2000 BCE (height 6.4 cm). Public Domain https://www.metmuseum. org/art/collection/search/324442. furnaces produced 98% pure copper and remained in use for at least 1000 years[4]. The Chalcolithic Age progressed slowly. The Bronze Age gradually arrived and the secrets of alloying copper with tin passed orally from families or guilds of skilled craftsmen. The cymbal’s exact place of birth is unknown, but China, East Asia, India, but once cast and worked into a cymbal, resonates with clarity and innumerable nuances of percussive sound. The fact that some cymbal manufacturers to this day keep the activities performed within the foundry off-limits to visitors and the public at large is testament to the continued tradition of mystery surrounding metal mixing, temperature parameters, and other traditional practices applied for making a given casting and continuing a family legacy. POURING MOLTEN METAL In antiquity, foundry workers poured molten metal into open clay or stone bowls (molds). This step of cymbal manufacturing remains unchanged, only the bowls are now clay graphite or other specialized cast iron (e.g., Meehanite)[6]. This step is deceptive in its simplicity; the goal is an ingot (bun) exhibiting a smooth, void-free surface without defects (Figs. 5-6). The size of the bun depends on the final cymbal size desired and may range from 2 to 20 lb. The challenges ancient metalworkers encountered (as do metalworkers today) during the pouring and solidification processes include pour temperature, pour rate, slag/dross removal, bowl temperature, reaction of metal at contact with bowl, type and application of bowl dressing, size of final casting, volume change from liquid to solid, temperature range of metal freezing, and dwell time in mold[7]. When using hand ladles, foundry workers must work in unison and develop a rhythm for transferring crucible and pouring molten metal. If using an auto-pour system (e.g., tilt-furnace) for pouring molten metal, the timing and weights are meticulously controlled; consistency and efficiencies are improved[8]. Tin bronze is a castable alloy which has a wide solidification temperature range (150° – 300°F)[9]. This wide freezing range is a challenge for metalworkers because segregation of the tin from copper may occur at grain boundaries, creating brittle areas which crack when hot worked (Fig. 7)[10]. Control of Fig. 2 — Bronze cymbal, Greece Late Helladic III, 1400–1060 BCE (8.0 cm diameter). Creative Commons: https://www.british museum.org/collection/object/ G_1872-0620-31. Fig. 3 — Copper alloy cymbal, excavated from Nimrud, Middle East, Iraq, North, 900-700 BCE. (height 3.5 cm, width 6.3 cm). Creative Commons: https://www.british museum.org/collection/object/W_N-116. or Anatolia are cited as places of origin in books concerned with the subject[5]. Many of the earliest cymbals of antiquity exhibited in museums are small (Figs. 1-3). These finger cymbals or clappers, which were connected by straps or handheld, underwent minimal change of form for hundreds of years. In the 21st century, foundries and artisans throughout Turkey, China, Japan, India, Thailand, and other East Asian and Southeast Asian countries continue the traditional practice of manufacturing cymbals. Similarly, throughout the world independent cymbalsmiths handcraft bronze cymbals for artists and other instrument markets. As in the ancient past, the metal used for achieving the most sonorous voice is high-tin bronze (known as bell metal) with tin content in the range of ~20%. ALLOYING Cu AND Sn Foundry workers melt copper and tin (Fig. 4), sometimes intentionally or unintentionally, alloyed with small quantities of other elements (Ag, Pb, and Fe), in a ceramic crucible. Traditionally, the heat source is a wood log and charcoal fire heating a stone oven, but foundries may use a crucible pit furnace. Modern foundries may use a high-frequency induction melt furnace and clay graphite crucibles. In ancient times, just as in modern foundries, a blanket of charcoal sprinkled over the molten metal provides protection against O2. The high-tin bronze and often “secret” mixture of copper and tin is the formula for creating bell metal used in cymbal casting. High-tin bronze is an alloy notoriously difficult to forge, Fig. 4 — Copper scrap (left and right) and tin ingot (top) for producing a high-tin bronze bun (bottom).
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