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An Observation on the meaning of Karat fineness


#1

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
average customer.

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
just me?

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.”

Charles Heick
Cincinnati, OhioDr. E. Hanuman Aspler
Webmaster


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#2

You’re making things much too complicated. That is, if your concern
is with the customer. There is carat and karat one referring to
weight and the other quality or fineness. The average customer is
more intelligent than you’re giving him or her credit for.


#3

Charles; In my humble opinion. Your observations are very
interesting and those of us in the trade should be aware of them.
However, delving into this without being asked by the customer AND
having perfected the digestability of our explanation, is a recipe
for yawns and a sales disaster. In other words, nobody but us nerds
cares. To demonstrate the depth to which I, myself, have have fallen
in the tar pit of chemistry, I got up from my bed the other night to
figure out the gram molecular concentrations of various alloys!
It’s fascinating and I suspect important in diffusion welding. Tom


#4

Dear Charles, While your analysis of volume versus weight may be
accurate (quite frankly I got bored with it half way through reading
it-which means all of my customers would be bored with it after
hearing 10% of it) the reality is that the reasons behind using 18k
are 1) the color of it is usually much richer looking (i.e. closer to
pure gold in color) and 2) it is a nicer metal to work with. I can’t
recall ever having this subject brought up in this way by a customer
and I live near MIT where we get scientists in all the time who want
to know everything there is to know about a metal. Quite frankly the
customer doesn’t need to know any more than the fact that the metal
is purer, a nicer (or different-some people simply prefer the color
of 14k) color and more expensive accordingly. Daniel R. Spirer, GG
Spirer Somes Jewelers 1794 Massachusetts Ave Cambridge, MA 02140
617-491-6000 @spirersomes www.spirersomes.com