|Palladium white golds
Palladium is the next choice for use in white gold alloys and, apart
from its high price and high melting point (1552 degrees celsius), is an
Additions of about 10 -12% palladium to gold impart a good
white colour. But palladium is an expensive metal and
it is also a heavy metal. Thus jewellery in such palladium white golds
will be more expensive than identical pieces in nickel whites for 2 reasons:
firstly, the cost of the palladium and secondly, the impact of density
- palladium white golds are denser and so such jewellery will be heavier.
It is also more difficult to process as the melting temperatures are
Many commercial palladium white golds only contain about
6-8% palladium plus silver, zinc and copper. Some may even contain some
nickel [so a palladium white gold is not necessarily nickel-free]. These
may also have less than a good white colour and so may also be rhodium
Palladium white golds tend to be softer and more ductile
compared to nickel whites and so generally will not wear as well. However,
despite its higher base cost and workshop recovery costs, making
a more expensive product, the advantages of a non nickel alloy now
out weigh these factors.
Alternative white gold alloys
In the European Union especially, there is a demand for
cheaper alternatives to white golds than the palladium whites which are
'nickel-free'. Many new alloys are coming to market, most of which rely
on manganese additions as the main whitener. Some are palladium-free
and others are low palladium alloys. Chromium and iron are also be used
as whiteners. They tend to be hard and more difficult to process. Many
of these alloys are not a good white colour, requiring rhodium plating,
and many suffer cracking problems and tarnishing.
We recently tried to anneal a batch of white gold from
Italy. It was so unmalliable we had to contact the manufacturer, and
whilst the solution was simple, a high street working jeweller would
find the new metals difficult, if not impossible to process.
Platinum, chromium, cobalt, zinc, tin and silver
are all used as whiteners. Silver has excellent working properties but
is poor as a whitener. Copper is also added to improve the ductility
of most white alloys.
It is important to remember that even the best white gold alloy
is actually grey, as is platinum. The white finish you are accustomed to is
a rhodium plating, and whatever you are told, white golds are only available
in caratages up to 21 carat. It is not possible to have a 22 ct white
Resistance to Tarnish
18 carat and 22 carat gold alloys are almost completely resistant to chemical
attack and 9ct alloys are much less resistant. Nine carat alloys can dull or
even blacken from exposure to chemicals in the atmosphere, and might discolour
in contact with household chemicals. 9ct chain is usually finished with a
deeper yellow 18ct or 22ct coating by manufacturers, which is why the bright
finish on a new 9ct chain gradually tones down to match other jewellery that
you wear on a daily basis.
The original bright finish
can usually be restored quite inexpensively by a working jeweller for little
cost should your chain become chemically or mechanically damaged over the
As well as affecting physical properties, alloying gold generally
increases the strength and hardness, with some reduction in malleability / ductility.
The silver atom is slightly larger than that of gold, so alloying gold with silver
gives a moderate improvement in strength and hardness. The copper atom is significantly
smaller than that of gold and so it has a greater effect on strengthening gold
than silver, as it distorts the gold crystal lattice more. Thus reducing caratage
from 24 carats through 22 ct down to 18 carat gold results in stronger
and harder alloys, but alloying beyond 18 ct down to 9 carat does not have
much further effect.