There is a thing in polishing which academics call "aggregation
and flow". In plain language - polishing medium builds up on front
edge of the piece. Then it breaks off and gets drugged under the
piece and comes out on another side. It is denser then the rest of
the medium and therefore acts as cutting component, destroying the
finish. It is precisely the reason why sometimes no matter how long
we polish, there are scratches.
Aggregation and Flow does not mean as you described, that the medium
being an aggregate is being swept, dragged or flowed through the
process. It refers to surface deformation through plasticizing and
associated relationships within the process. This has been well
covered and discussed in Lapidary circles for a loooooong time.
It refers to surface deformation through plasticizing and
associated relationships within the process. This has been well
covered and discussed in Lapidary circles for a loooooong time.
aka Beilby layer formation. It can be looked at it that way, but
abrasive must be softer than material been polished. I am not sure if
it is applicable to tripoli on gold.
aka Beilby layer formation. It can be looked at it that way, but
abrasive must be softer than material been polished. I am not sure
if it is applicable to tripoli on gold.
Leonid, No, not exactly. The Beilby theory was a ‘flow’ theory.
Current polish science deals with the exchange of charged pos/neg
ions in a plastic environment. As Al said '…and associated
relationships within the process". Beilby’s theory was discredited
looong ago not for its predicted result but for the wrong process in
achieving the result.
I am not disputing your point on what possibly happens during
polishing, to be a cause of underlying problems.
I’m disputing the terminology you used to describe it
It refers to surface deformation through plasticizing and
associated relationships within the process. This has been well
covered and discussed in Lapidary circles for a loooooong time.
aka Beilby layer formation. It can be looked at it that way, but
abrasive must be softer than material been polished. I am not sure
if it is applicable to tripoli on gold.
Beilby attributed the polish on metals to creating a layer of
amorphous metal on the surface resulting from rubbing, which causes
the metal to flow and then harden as a supercooled liquid. His book
“Aggregation and Flow of Solids” is a very good read (although a
little heavy at times) to better understand what really happens when
any form of friction is introduced into a process.
Steve Attaway wrote an article about Gem polishing many moons ago
which I enjoyed reading then, and did so again when I managed to find
it online. It does touch on the subject briefly.
Beilby attributed the polish on metals to creating a layer of
amorphous metal on the surface resulting from rubbing, which
causes the metal to *flow* and then harden as a supercooled liquid.
In the 90’s the Beilby layer was examined via TEM (Transmission
Electron Microscopy). It was found to be a microcrystalline layer
rather than the amorphous structure that Beilby hypothesized. The
layer is there and effects several of the properties of the surface
but it is still a crystalline structure.
Steve Attaway wrote an article about Gem polishing many moons ago
which I enjoyed reading then, and did so again when I managed to
find it online. It does touch on the subject briefly.
Terminology can be a problem from time to time, so not to confuse
things, I am withdrawing term “aggregation and flow” from the
discussion. That said, I have seen it in literature on polishing in
this context.
As Al said '.....and associated relationships within the process".
Beilby's theory was discredited looong ago not for its predicted
result but for the wrong process in achieving the result.
Yes, Beilby layer is a controversial subject. I still like to call
the effect “Beilby Layer” because he may got the processes wrong, but
his observations were spot on. Anyhow, I do not think it applies to
polishing with tripoli.
In the 90's the Beilby layer was examined via TEM (Transmission
Electron Microscopy). It was found to be a microcrystalline layer
rather than the amorphous structure that Beilby hypothesized. The
layer is there and effects several of the properties of the
surface but it is still a crystalline structure.
What took you so long?..
First of all I agree with your point.
I am however going to throw a curve ball here and make it a little
more interesting.
They were experimenting a few years ago with Oxide Scales and their
ability to develope a protective and wear resistant layer through a
process of self alignment in certain alloys which apparently did
create an amorphous layer through polishing and temperature if I
recall correctly.
I did suspect at the time that instead of Aggregation or Cohesion
like Beilby thought, it lent itself more to Adhesion, but I don’t
really recall the specifics.
If you are interested I will look to see where I can reference that
for you. All I remember was that it had some chrome in the alloy.
