With the current discussion on 18KW gold, it seems like a good time
for me to bring up for discussion my thoughts on the perception of
the term Karat.
How do you perceive Karat fineness? I’m sure we all know what it
means. Karat fineness refers to weight, but we live in a visual
world. Our vision senses volume, not weight. And the relationship
between volume and weight, Specific Gravity, affects how much of a
particular type of metal we see; what actually comes into contact
with our skin.
As I wrote previously in my introduction a couple of years ago, I am
learning Gemology and the jewelry trade, and am currently taking GIA
courses. Granted, at a slower pace than desired. My background is
in engineering with mineralogy and geology as lifelong interests.
For myself, as I reflect on the true meaning of Karat fineness, I
find what seems to me to be a deceptiveness in ones perception of
it. In other words, how much gold is there in an item of a
specified Karat rating and how is that amount perceived by the
For example, lets say a customer is looking at gold wedding bands
and you show that person an 18KY gold band and proceed to describe
its merits. The customer then asks “what exactly do you mean by 18K
and how much gold does it contain.” You then proceed to explain the
meaning of the term Karat and that the ring is 75% gold by weight.
The customer, knowing nothing of SG, may then visualize a quarter
section of the circumference of this ring removed, like a quarter
piece of a pie, and what’s left as being fine gold. This perception
by the customer would be wrong. In terms of volume, which this
customer is visualizing, 40% of the ring would have to be removed
for the remaining metal to indicate the fine gold content, not 25%.
I’m speaking of volume here. After all, it’s volume that occupies
space, not weight. This is the deception that may mislead a
customer and maybe some reading this, if you haven’t put Karat
fineness in it’s proper perspective.
I played around with the numbers and came up with some formulas.
Formulas that surely have preceded me. I did this to prove a point
that many of you probably already know, but that causes me to have a
new outlook on the meaning of the term Karat. And that is, as the
Karat rating lowers, the actual gold content by volume drops at a
disproportionate rate. A rate so much greater, that the actual
amount of gold by volume is disappointingly anemic.
Lets use the 18KY gold ring in a basic alloy (by weight): gold 75%,
silver 12.5% and copper 12.5%. The gold (Au) has a specific gravity
of 19.3, the silver (Ag) 10.6 and the copper (Cu) 8.9. This means
you have 1.820755 times more silver by volume than gold of the same
weight and 2.168539 times more copper by volume. Therefore, using
75% for Au as a reference for this 18KY alloy mix, it contains:
75.000% gold by volume ( 75 x 1 )
22.759% silver by volume ( 12.5 x 1.820755 )
27.107% copper by volume ( 12.5 x 2.168539 )
124.866% total volume over fine gold of the same weight
Now, we remove the excess volume of metal, 24.866%, and the
remaining Au content is 60.064%. % gold by volume (18KY) = 75 x
(1/(124.866/100)) = 60.064%
Specific Gravity (18KY) = ((.75 x 19.3) + (.22759 x 10.6) + (.27107
x 8.9)) / 1.24866 = 15.46
Here are the calculations I came up with for other gold alloys:
% By Weight % Au
Karat Au Ag Cu Zn by Volume SG
22KY 92 4 4 85 17.9
18KY 75 12.5 12.5 60 15.5
14KY 58 25 17 41 13.7
10KY 42 12 41 5 25 11.6
Note: Zinc (Zn) has a SG of 7.1 or 2.71831 times more by volume than
gold of equal weight.
For a 10K item, only 1/4 of the space that the object occupies is
fine gold. In a 14K band, much less than half of it is actually
gold, 41%. Remember, I’m writing of volume here; the space the gold
occupies. Is this somewhat deceptive of ones perception or is it
We need a standard of measurement and no standard is going to be
perfect. Whether it’s the Moh’s scale for hardness or Karat for
fineness, a misconception is likely to occur unless the person
interpreting it fully understands that system.
I would enjoy reading what others have to write concerning this. As
John Dewey once said, “Education is not preparation for life,
education is life itself.”
Cincinnati, OhioDr. E. Hanuman Aspler
[ G a n o k s i n . C o m ]