Contrasting The Hypoallergenic
Potential of
14-Karat Gold And Surgical Stainless Steel |
A report by Professor. John
Zotos,
Materials & Metallurgical Consultant & Lecturer
Pure gold has a low chemical
affinity for most elements and compounds, and its resistance
towards corrosion and/or interaction with the human skin arises
from this fact rather than from the formation of passive films
on its surface. Additions of silver, and particularly copper,
lower the nobility of gold somewhat. At room temperature levels,
gold alloys can go down to as low as 50 atomic per cent gold,
i.e., 65 weight per cent gold in the case of silver alloys and
about 75 weight per cent gold for the copper alloys, and still
possess good passivity towards the human skin. Thus, 18 karat
gold alloys (75 weight per cent) would be very safe and should
not be hypersensitive when they come into contact with the human
epidermis. (1)
Surgical, non corrosive grades of stainless steels are derived
from a family of ferrous alloys classified as being austenitic
and their crystal structure is face centered cubic. The normal
analyses of the various grades of austenitic stainless steels
are delineated in the literature. (2) Completely homogenized
austenitic stainless steels possess optimum resistance to corrosion
and in this state they will not interact with the human skin.
The condition is achieved by rapidly cooling all of these alloys
from their solution temperature ranging from 1900 F to 2000 F.
The presence of annealing twins in the micro-structure of this
material proves that it is a fully homogenized state and thus
is in an optimum condition for sustained hypoallergenic behavior,
i.e., it should be non hypersensitive when it comes into contact
with the human epidermis. A special etching solution can be used
to reveal such a structure in this family of stainless steel
alloys. (3)
Since pure gold is classified
as being 24-karat, the 14-karat gold alloys contain only 58.3
weight per cent gold. This simply means that all 14-karat gold
alloys are lacking sufficient passivity towards the human skin
whether they are used in earrings and/or other types of contact
jewelry products since they are 6.7 weight per cent gold below
the critical level for silver alloys and 16.7 weight per cent
below for copper alloys.
Thus, fully annealed, surgical
grades of austenitic stainless steels quenched from their solution
temperatures should have a homogeneous microstructure and a far
greater hypoallergenic potential than any 14-karat alloys. |