Guidelines for the Technical Examination of Bronze Sculpture

**Table 9**
**Hardness and machinability of various modern as-cast copper alloys**
After Tyler and Black 1992, table 3. Machinability is scaled against the most machinable alloy, namely “free-cutting brass C3600” (35.5% Zn, 3% Pb). Names of alloys are those most commonly used for bronze sculpture.
Alloy name (author’s nomenclature)	Alloy number (Amercian Society of Metals [ASM] nomenclature)	Composition (wt%)	Hardness (Brinell 500kg)	Machinability (%)
pure copper	C80100	99.95% Cu	44	10
tin bronze	C90200	7% Sn	70	20
tin bronze	C90700	11% Sn	80	20
leaded tin bronze	C92700	10% Sn, 2% Pb	77	45
leaded tin bronze	C93700	10% Sn, 10% Pb	60	80
ternary alloy	C90500	10% Sn, 2% Zn	75	30
quaternary alloy	C92600	10% Sn, 1% Pb, 2% Zn	70	40
quaternary alloy	C83300	1.5% Sn, 1.5% Pb, 4% Zn	35	35
quaternary alloy	C83600	5% Sn, 5% Pb, 5% Zn	60	84
quaternary alloy	C83800	4% Sn, 6% Pb, 7% Zn	60	90
brass	C83400	10% Zn	?	60
high-zinc brass	C85400	1% Sn, 3% Pb, 29% Zn	50	80
silicon bronze	C87200	4% Si (89% min Cu)	85	40

Table 9: Hardness and machinability of various modern as-cast copper alloys