10. Ease of casting – high density, good
fluidity
Cost – inexpensive material/labour
11. Gold alloys with at least 75%
noble metals
Proportion of gold in alloy
Carat rating – number of 24th parts of gold
Finess rating – parts/thousand of gold
14. Alloy Composition:
Noble Metals
Gold (Au) *
Platinum (Pt) *
Palladium (Pd) *
Iridium, Ruthenium, Niobium, Osmium
Resistant to corrosion and tarnish
Gold was the first metal successfully used
copper & silver added to enhance it
15. Precious Metal = containing metals of high
economic value such as gold, platinum,
palladium, silver, (rhodium), (iridium),
(rhuthenium), and (osmium).
Noble Metal = a precious metal that is
resistant to tarnish. This excludes “silver”
by definition
16. Classification and composition
Ty
pe
Descripti
on
Minimum
total
amount of
noble
metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I
(A)
Soft 83 80-90 3-12 2-5 Little/no
ne
Little/no
ne
Little/no
ne
II
(B)
Medium 78 75-78 12-15 7-10 0-1 1-4 0-1
III
(C)
hard 78 62-78 8-26 8-11 0-3 2-4 1
IV
(D)
Extra hard 75 60-70 4-20 11-16 0-4 0-5 1-2
17. Effects of Alloys Components:
(1) Gold (Au)
(2) Copper (Cu)
(3) Silver (Ag)
(4) Palladium (Pd)
(5) Platinum (Pt)
(6) Zinc (Zn)
Corrosion resistance
Hardness
Counteract orange color of
copper
Increase MP and hardness
Increase MP
Prevent oxidation during
melting (O2 getter)
18. Classification and composition
Ty
pe
Descripti
on
Minimum
total
amount of
noble
metals
Au (%) Ag (%) Cu (%) Pt (%) Pd (%) Zn (%)
I
(A)
Soft 83 80-90 3-12 2-5 Little/no
ne
Little/no
ne
Little/no
ne
II
(B)
Medium 78 75-78 12-15 7-10 0-1 1-4 0-1
III
(C)
hard 78 62-78 8-26 8-11 0-3 2-4 1
IV
(D)
Extra hard 75 60-70 4-20 11-16 0-4 0-5 1-2
19. Dental uses
Type I – situations where there is no
great stress
Cl III
Cl V