I have always been taught to dip my piece in boric acid and alcohol
before soldering. Of course, we all do that. But here is my question,
does it allow a small measure of thermal protection on diamonds or
not? I was taught that in school and know many jewelers who believe
this as well. But yesterday I was talking with a jeweler who said
that was nonsense. He never heard of such a thing. What is the
general consensus of this panel?
LaVerne
It does not provide any thermal protection but it does provide an
oxygen barrier so you don’t burn the diamonds, they are carbon after
all.
Jim
James Binnion
James Binnion Metal Arts
the coating of boric acid protects the surface of the diamond from
oxygen not heat. It is the oxygen that is the cause of the daimond
"burning". Think of how the boric acid dip keeps your gold from
turning black during soldering. Again it is not he heat but the
introduction of oxygen to the unprotected surface that turns the
metal black, same with a diamond.
From what I understand, it protects the diamond’s surface from being
"burnt" by excess oxygen.
But here is my question, does it allow a small measure of thermal protection on diamonds or not?
Well, technically, since that very thin layer of boric acid is not as
good a thermal conductor as the diamond is, one supposes that it at
least slightly delays or very slightly slows the heat rise. But that
effect would be for all intents and purposes, negligable. It protects
the diamonds from the effects of heating in an oxygen containing
atmosphere, not from the actual heat, or really, the rate of heating.
The layer is just too thin to do that. But the important part is that
it does protect the diamonds from the thing they need protecting
from, and that is oxygen while heated. After that, within reasonable
temperature ranges, so long as the layer stays intact and doing it’s
job, the diamond won’t burn, which is the whole point.
Peter
But here is my question, does it allow a small measure of thermal protection on diamonds or not?
Boric acid doesn’t provide protection from heat, but from oxygen,
which is very reactive at high temperatures.
Larry
I was taught that in school and know many jewelers who believe this as well. But yesterday I was talking with a jeweler who said that was nonsense
Richard, the next time that jeweler pipes up, you should find
something useful to do with your time. It’s not belief, it’s science.
Without the coating, they will burn, with it, they will not - this
being in the reasonable soldering temperatures. Diamond is carbon,
and without a coating to exclude oxygen is will act like carbon under
heat.
I have read all the opinions expressed on the subject and I would
like to offer a different view on the subject. I do not want to start
an argument, just to demonstrate how wrong group thinking can be.
There are two issues here: protection from thermal shock and the
danger of setting diamond on fire. Thermal shock: substances which
are
vulnerable to thermal shock, are substances which do not conduct heat
well. That been the case, parts of such substance become overheated,
while other parts remain less heated; that causes unequal expansion
and it shutters. Regular glass belong to this class. Diamonds are one
of the best conductors of heat in existence. Diamond heat conduction
is so good, that one heat the diamond to red heat and plunge it into
liquid nitrogen without any danger of shuttering.
Danger of burning diamond: diamonds do burn, but in order for
reaction to start, diamond has to reach temperature of 1562 degrees
Fahrenheit. Due to high thermal conductivity of diamonds, even if the
piece itself would reach such temperature, the diamonds would be few
hundred of degrees cooler. In another words, the piece been worked
on, would melt before diamonds would reach required temperature to
trigger reaction of oxidation ( burning ).
Why then we do it? It is to protect the metal under the diamond from
oxidation. Diamonds themselves are quite save. Also, by dipping it in
boric acid - alcohol solution, the piece is degreased. If there are
grease on diamonds, such stones may require repolishing if brought to
high temperatures, but not due to diamond burning. That is the true
reason for the practice.
Leonid Surpin
There are two issues heRe: protection from thermal shock and the danger of setting diamond on fire. Thermal shock: substances which are vulnerable to thermal shock, are substances which do not conduct heat well. That been the case, parts of such substance become overheated, while other parts remain less heated; that causes unequal expansion and it shutters.
While low thermal conductivity is an aspect of thermal shock
cracking it is not the only reason. There is also toughness and
thermal expansion coefficient. Fused quartz is a poor thermal
conductor but is very thermal shock resistant because of its low
thermal expansion coefficient and while it is moderately tough when
compared with diamond it is quite tough when compared to other
ceramics.
Regular glass belong to this class.
But borosilicate glass (Pyrex) is highly resistant to thermal shock
cracking and is not markedly different from regular “soft” glass in
its thermal conductivity. However it has a lower thermal expansion
and greater toughness than regular glass.
Diamonds are one of the best conductors of heat in existence. Diamond heat conduction is so good, that one heat the diamond to red heat and plunge it into liquid nitrogen without any danger of shuttering.
Again very low thermal expansion and excellent toughness along with
the greatest thermal conductivity of any material and if it is a
colorless or near colorless F or IF stone or a clean lab created
diamond this would be no problem. But you try that with a SI1 and
you are liable to remove that diamond from the liquid nitrogen in
several pieces. Which is why it is not a very good idea to quench
that diamond ring after re-tipping.
Danger of burning diamond: diamonds do burn, but in order for reaction to start, diamond has to reach temperature of 1562 degrees Fahrenheit. Due to high thermal conductivity of diamonds, even if the piece itself would reach such temperature, the diamonds would be few hundred of degrees cooler. In another words, the piece been worked on, would melt before diamonds would reach required temperature to trigger reaction of oxidation ( burning ).
While you might be able to set up such a scenario it is unlikely in
typical repair work that the diamond will be significantly cooler
than the surrounding metal. The main reason for this is that the
diamond is in thermal contact with the metal and will act as a very
good heat sink till the difference in temperature between the diamond
and the metal is fairly low. Also the boric acid will act to increase
the thermal contact between the stone and the metal lowering the
thermal impedance between the diamond and the metal due to the
increased surface area of contact. In the common job of re-tipping a
prong on say a.5 carat stone as long as the diamond is sucking away
the heat you will not be able to raise the prong tip to the point
where the solder will flow till the diamond is very near the flow
point of the solder because of this heat sinking.
Why then we do it? It is to protect the metal under the diamond from oxidation. Diamonds themselves are quite save. Also, by dipping it in boric acid - alcohol solution, the piece is degreased. If there are grease on diamonds, such stones may require repolishing if brought to high temperatures, but not due to diamond burning. That is the true reason for the practice.
Since the majority of the time that one would be soldering around a
diamond is in repair operations so I am sure you rely on something
more than the alcohol in the fire coat to clean and degrease the
stone as this would be insufficient for anything more than
fingerprints or other very light soil. Because most of the diamonds I
see in repair jobs are filthy.
James Binnion
James Binnion Metal Arts
In another words, the piece been worked on, would melt before diamonds would reach required temperature to trigger reaction of oxidation ( burning ).
Having burned a few diamonds, I think I’ll just use the dip…
Since the majority of the time that one would be soldering around a diamond is in repair operations so I am sure you rely on something more than the alcohol in the fire coat to clean and degrease the stone as this would be insufficient for anything more than fingerprints or other very light soil. Because most of the diamonds I see in repair jobs are filthy.
Since cleaning jewellery for repair was beyond the scope of the
discussion, I feel justified to omit step-by-step instruction. But
point well taken. Jewellery must be absolutely clean before
attempting
to solder. Alcohol is the last step in this process to eliminate
traces of handing and drive off whatever moisture may be present.
Leonid Surpin