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Ionic vs ultrasonic cleaner


#1

I need to buy a cleaner and am not sure whether to go with an
ultrasonic or an ionic (speedbrite) unit. I can only afford one. Any
advice on which technology or which models to go with?

Thanks,

Ellen


Home Made Ionic / Ultrasonic Cleaner
#2

Hi Ellen,

I need to buy a cleaner and am not sure whether to go with an
ultrasonic or an ionic (Speedbrite) unit. I can only afford one. Any
advice on which technology or which models to go with?<<

I’ve got both, the Speedbrite & a Gemoro ultrasonic. Which I use
depends on what I want to clean. If I’m cleaning a ring or something
with lots of gunk around the smaller parts, I use the ultrasonic. If
I’m trying to brighten up a sterling chain, I usually use the
Speedbrite. If the chain has lots of gunk in it, it’ll probably go
into the ultrasonic 1st, then into the Speedbrite.

The ultra sonic cleans by cavitation, millions of little bubbles
impinging on the dirt, causing it to loosen & come off the item.

I’ve never seen a write-up on the cleaning mechanism at work in the
Speedbrite, but I’d suspect it’s a mild form of electro-stripping. The
item to be cleaned is attached to the positive lead of a approx. 16
volt direct current (DC) power supply. The negative lead is a plate
under the plastic screen in the bottom of the Speedbrite tub. The
liquid in the tub acts as the electrolyte when the unit is in
operation. The oxidation on the item is attracted to the cathode
(negative plate on the bottom of the tub), restore the surface of to
some of its’ former glory. I always polish an item with a buff or
tumbler after it comes out of the Speedbrite (same for the
ultrasonic).

Speedbrite makes an add on unit for ultrasonics. I’ve not examined
one up close, but suspect it’s a power supply that uses the metal tub
of the ultrasonic as the cathode & the a positive lead from the unit
as the path to the item to be cleaned. You probably have to provide a
plastic basket to be placed in the ultrasonic since the item to be
cleaned cannot be in direct contact with both the positive & negative
side of the DC power supply.

If I could only have 1 cleaner in the shop, it’d be an ultrasonic.

Dave


#3

Ellen, what type of cleaning job are you doing ? They’re both
different machines. If you want to clean up after using the abrasive
compounds or polishing agents, then you need the ultrasonic cleaner.
If your finished jewelry has tarnished and you want to remove it,
then use the ionic cleaner; it will also loosen up the dirt that has
accumulated behind the gemstones and bring it back to life. The
ultrasonic machine will not remove tarnish and you should never place
any jewelry with fragile gemstones or stones that have inclusions and
fractures. With the ionic cleaner, such stones are OK.
Min Azama in Tokyo


#4

Hi Everyone,

Dave is right about the different uses for the different cleaners.
Another consideration is the type of stones you will be placing in the
cleaners. Some stones absolutely cannot be placed in an ultrasonic.

So think about that as well.

I would like to clarify the description of how an ultrasonic works.
The statement that tiny air bubbles are responsible for cleaning is
not accurate. Actually air in the liquid hinders any cleaning. If you
notice when placing fresh tap water into an ultrasonic and turning it
on a lot of air will be forced out of the water right away and as all
of the air is removed from the water the ultrasonic will clean
better. This is because the air being flexible absorbs the ultrasound
waves. This is also why using plastic in an ultrasonic will greatly
reduce the cleaning ability. Anything you put into the cleaner that is
not a rigid solid will absorb and diminish the ultrasonic activity.
That’s why glass beakers and steel trays and baskets are used. They
pass the ultrasonic wave right on through without impeding them.

The ultrasonic produces ultrasound waves. Ultrasound is not audible.
The ultrasound waves are transmitted into the solution and these very
compact and very high frequency waves are what actually ‘tear’ apart
the dirt and grime. There are many different uses for ultrasound and
not all frequencies are capable of cleaning. That is why there are so
many different manufacturers of the cleaners. Each has a different
belief in what the right frequency is and the methods to achieve that
frequency. Usually the faster a cleaner cleans the faster it will
self destruct. All ultrasonic cleaners will destroy themselves
eventually. They all can be repaired like new. It is a trade off. How
fast do you need your items cleaned vs. how long do you want your
cleaner to last before needing to be repaired. The manufacturers are
all very competitive and are making advancement everyday to improve
the effectiveness of their brands. In my opinion some brands are
better than others in general. Again if you need to clean fast and
have a high volume of cleaning to do you will want a cleaner that will
self destruct sooner or if you have the finances maybe several
cleaners that will live longer and clean slower are a better choice,
or a much larger unit that cleans slower would work. There are a lot
of trade-offs to consider. Purchasing an ultrasonic cleaner is
probably on of the more difficult buying decisions to make.

I have seen and repaired most of the brands on the market and I have
some very strong opinions as to which are made best and made to last
and clean the best. Because ultrasonic cleaners have so many variables
built into them one thing you will find among all that use them is a
lack of agreement as to which is the best. If you want to talk more or
have any other questions and would like to talk to me call me toll
free at 877-262-2185. I would be happy to explain more about this to
any one.

It should be one item that is studied thoroughly before purchasing so
you will be happy with the unit. Too many people buy an ultrasonic
cleaner because of price and don’t do the research to find out if it
will really do what they want. Most that buy this way are not
satisfied. There are some very cheap units out there but in this case
they may not be right for you.

One last thing when I said they all self destruct I meant this
literally. The industry standard test is to place a piece of aluminum
foil suspended in the solution and turn the unit on. Within 1 minute
the unit should have torn holes in the foil. The pattern of the holes
should be spread out over the majority of the foil and should be small
to medium in size. If allowed to continue running the foil should
disintegrate. This same action is being applied to the tank.
Therefore the movement that is used to create the ultrasound eats away
at the tank. Eventually holes in the tank will occur. Most times they
are smaller than a pin head and can only be seen by placing a bright
light under the tank and looking for them from the top. Although tell
tale signs are where there is dried or semi-dried soap solution on the
bottom of the tank.

All ultrasonic cleaners are not created equal!

I will be writing an article about ultrasonic cleaners for the e-zine
’Eclectic Lapidary’ that will also cover these and other issues. Look
for it soon.

Ken Kotoski
MPG Repair
www.mpgrepair.com


#5

Hi Ken!

Thanks for the valuable insight! Can you give us any tips on what
not to do with or ultrasonics? You said don’t use plastic - which
I’m glad you did because I’ve uses a little plastic basket for small
parts.

I’ve also vague heard warnings along the lines of not allowing
anything to touch the tanks wall when the unit is on, don’t heat the
untrasonic for silver, etc.

Any additional suggestions on prolonging the life of them, and things
to avoid would be great!

Thanks again,

Dave

Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com mailto:dave@sebaste.com


#6
I would like to clarify the description of how an ultrasonic works.
The statement that tiny air bubbles are responsible for cleaning is
not accurate. Actually air in the liquid hinders any cleaning. 

In fact, these are not air bubbles. They are gas bubbles of the
liquid that is being used in the ultrasonic. They are microscopic and
form and collapse almost instantaneously. They are much like the
bubbles that form and collapse on the bottom of a pot of warming water
before it can boil. Due to the low twmperature of the surrounding
water these bubbles instantly recondense without surfacing. This
formation and collapse of these gas bubbles in ultrasonic cleaners is
called cavitation.

Bruce D. Holmgrain
JA Certified Master Bench Jeweler
HTTP://www.goldwerx.com


#7

Hi Dave,

Here is what you asked for. Some of this I’m sure most of you know.
However if anybody knows about proper cleaning of the sonic I have
never seen evidence of it! So read on and if you have any questions
about sonics or other equipment don’t hesitate to email me at
ken@mpgrepair.com or call toll free at 877-262-2185. I feel very
strongly about helping everyone in the industry with and
saving them money by repairing all equipment.

A small metal basket would be better for small parts. Just be sure to
suspend it above the tank bottom and don’t place it in or take it out
of the cleaner while it is running.

Most ultrasonics have electrical safety built into them to 'reduce’
the chance of someone getting an electrical shock from the tank but
things do happen. Having worked on them for years I can tell you that
you don’t want to be shocked by them! It’s not a little tingle like
from a 120 volt outlet. A little side note heRe: Voltage does not harm
you it’s the amperage that does. So you could touch a line that has
1000 volts and no amperage and it wouldn’t do anything to you but add
a small amount of amperage and it could have serious effects.

The circuits in ultrasonics create very high voltages and small
currents (amperage) to make the transducers create the ultrasonic
waves. The transducers are mounted (usually glued with specific epoxy)
directly to the tank bottom. Therefore there is always a possibility
that something could go wrong and the electricity could be ‘live’ on
the tank and in the solution. So by placing your fingers, hands or
any metal object in the solution or touching the tank could close a
circuit through you and give you a very bad electrical shock.

Don’t drop anything heavy on the bottom of the tank. The transducers
are ceramic crystals that are fragile. They can be broken if this
happens.

Other way crystals get broken are by running the cleaner without
solution or very little solution in the tank. Or when changing the
solution be sure the old solution has cooled down before replacing it.
When a sonic has been running the transducers get hot. If they are
suddenly cooled it can crack them.

Having started and run a production shop where we produced all kinds
of findings I can understand that equipment upkeep is sometimes
difficult. But it is essential to the overall longevity of your
equipment. As with all equipment regular service and/or care needs to
be done. For an ultrasonic: it should be wiped down with a water
moistened cloth each day to remove the soap that has been splashed
and dripped. Most soaps are caustic and if left on the unit will start
to eat away the metal parts. Also if they are allowed to build up they
can eventually get to the circuit board and cause shorts. When
cleaning the unit DON’T ever put it under water (running or
otherwise). The sonics are not sealed and when water gets inside it
will get to the circuit. The lack of wiping the unit down daily is the
cause of the majority of sonics failing. This is an accumulated
problem. It happens over a period of time not right away.

When running the cleaner be sure the liquid is at the proper level.
If the unit is heated this means not less than 1" below the rim of the
tank. The heating elements are placed on the side of the tanks and on
smaller units (less than 1 gal.) the heating elements normally are
about 1" down from the rim. The heating elements are designed to
produce a significant amount of heat for their size and without the
solution covering them they will burn out. If your unit is not heated
the same liquid level is suggested however it is not as critical. The
level could go down an inch or so before you endanger the transducers.

The type of solution you use can cause problems for your ultrasonic.
Water with a very little amount of soap is the recommended solution.
Unless you have specifically purchased a unit from the mfg. that is
made for ammonia or other degreasers do not use them. The sonics that
are sold in the jewelry and dental industries are not made for it and
when placing ammonia in one, the cleaner will change it into a mild
acid. Also some manufacturers have found that ammonia and red rouge
for some reason will attack the circuit. The last time I talked with
them they still had not figured out what was happening.

The tank being metal will wear out with use on all units. When the
transducers are working the electrical pulses force them to physically
change shape. This shape changing is what creates the ultrasound. When
the transducers change shape this motion is transmitted to and through
the tank. Imagine taking a piece of sterling flat stock that is 1/2
hard and bending it back and forth many times. What happens? There
will be a line where the metal gets progressively weaker until it
breaks. Just before breaking it will have developed very tiny holes in
that weak area. This is the exact same thing that is happening to your
sonic tank. All of the smaller sonics use tanks that have been drawn
down. So the weakest and thinnest points are the corners. These are
the places normally that will form tiny holes first. Some cleaners
operate at frequencies that will cause the tank to deteriorate where
the transducers are mounted. The more aggressive the cleaner is the
faster these holes will be created.

One manufacturer claims that in their unit if metal filings are left
on the bottom of the tank this too will increase the speed of tank
deterioration. This mfg. makes one of the most aggressive ultrasonic
cleaners on the market.

When running your cleaner don’t let anything rest on the bottom
unless it is plastic or rubber. Again if metal is placed on the bottom
of the tank the vibration will eventually rub a hole in the tank. On
an ultrasonic the last thing you want to replace is the tank. The
reason is that you can’t just replace the tank. The transducers have
to be replaced as well. They cannot be salvaged. So if you have a
basket that sits on the bottom of the tank rather than being
suspended make sure it has plastic or rubber feet on it. These baskets
are not ideal for other reasons as well. Anything that sits on the
bottom of the tank will reduce the ultrasonic activity. It dampens the
ability of the transducers to move the tank bottom. The best way to
clean parts is to suspend them. There are many ways to do this. A
basket that uses the rim of the tank for support, a suspended beaker
or a wire (insulated).

Again when using any metal object in the cleaner be sure the unit is
off before removing it or use some kind of electrically insulated
covering on your hands to remove it. I have never gotten shocked this
way but I have gotten shocked from transducers. Transducers can create
a large electrical charge from being heated and cooled, by striking
them or applying pressure. They hold the charge for a very long time
if not discharged and when replacing them it is easy to get shocked
from them a couple of times. Believe me when I say it will only happen
a couple of times! After that you have a fear of being shocked so
strong that you can block out a nuclear explosion if it was set off
right next to you! A shock from the cleaner while it is running is
much worse.

Always make sure the ground prong on the plug is in good shape. Don’t
remove it. It needs to be there for safety. If your outlet doesn’t
accept a 3 prong plug change the outlet.

When adding soap to the water in the tank it is better to have too
little than too much. The first and most important job of the soap is
to reduce surface tension so the water will degauss. Remember any
trapped gas in the solution will hinder the sonics ability to work at
top efficiency. After degassing the soap will have some ability to
help clean. However too much soap will reduce the effectiveness of
the ultrasonic activity. The ultrasonic action uses the molecules in
the solution to clean or tear the dirt off the item by stretching them
and them collapsing them rapidly. So any trapped gases will act as a
cushion and will not allow the ultrasonic to work as well as it
should. Think of it this way. If you took a hammer to a ball what
happens? The hammer will slightly collapse the ball and the hammer
will be bounced off of it but the majority of the force will be
absorbed by the ball. The ball in this case is gas in the solution and
the hammer is the ultrasonic waves. All soaps for any purpose have as
one of the very fist ingredients a wetting agent. This allows the
water to become wetter and reduce surface tension. In our use this
allows the gasses to be expelled quickly. Try this experiment: Empty
your cleaner. Rinse it and place fresh tap water in it. Turn it on.
You will see some of the gasses come to the surface. If you let it run
for several hours the majority of the remaining gasses will come out.
But instead place a drop or two of soap in the water while it is
running. Within a few minutes you will see a large amount of gas
coming out.

This gas that is released is released because the surface tension has
been reduced. If you were to try and clean a part without the use of
soap you would find it takes a very long time. This is because of high
surface tension. And you don’t want your pieces to be in an ultrasonic
for long. If you remember my last post with the aluminum foil. The
ultrasonic can do this same thing to your pieces if left in too long.

As far as heating for silver. I can’t understand why not. Unless
someone is using some chemical that would cause a reaction. It may
have to do with the fact that they didn’t rinse the soap off the parts
after cleaning and when it cooled it tarnished. But if you use water
and soap then rinse you shouldn’t have a problem. The heat will help
loosen and greases or oils on the piece.

I hope this helps. Take care.

Ken Kotoski
MPG Repair
www.mpgrepair.com


#8

Hi Dave,

Here is what you asked for. Some of this I’m sure most of you know.
However if anybody knows about proper cleaning of the sonic I have
never seen evidence of it! So read on and if you have any questions
about sonics or other equipment don’t hesitate to email me at
ken@mpgrepair.com or call toll free at 877-262-2185. I feel very
strongly about helping everyone in the industry with and
saving them money by repairing all equipment.

A small metal basket would be better for small parts. Just be sure to
suspend it above the tank bottom and don’t place it in or take it out
of the cleaner while it is running.

Most ultrasonics have electrical safety built into them to 'reduce’
the chance of someone getting an electrical shock from the tank but
things do happen. Having worked on them for years I can tell you that
you don’t want to be shocked by them! It’s not a little tingle like
from a 120 volt outlet. A little side note heRe: Voltage does not harm
you it’s the amperage that does. So you could touch a line that has
1000 volts and no amperage and it wouldn’t do anything to you but add
a small amount of amperage and it could have serious effects.

The circuits in ultrasonics create very high voltages and small
currents (amperage) to make the transducers create the ultrasonic
waves. The transducers are mounted (usually glued with specific epoxy)
directly to the tank bottom. Therefore there is always a possibility
that something could go wrong and the electricity could be ‘live’ on
the tank and in the solution. So by placing your fingers, hands or any
metal object in the solution or touching the tank could close a
circuit through you and give you a very bad electrical shock.

Don’t drop anything heavy on the bottom of the tank. The transducers
are ceramic crystals that are fragile. They can be broken if this
happens.

Other way crystals get broken are by running the cleaner without
solution or very little solution in the tank. Or when changing the
solution be sure the old solution has cooled down before replacing it.
When a sonic has been running the transducers get hot. If they are
suddenly cooled it can crack them.

Having started and run a production shop where we produced all kinds
of findings I can understand that equipment upkeep is sometimes
difficult. But it is essential to the overall longevity of your
equipment. As with all equipment regular service and/or care needs to
be done. For an ultrasonic: it should be wiped down with a water
moistened cloth each day to remove the soap that has been splashed and
dripped. Most soaps are caustic and if left on the unit will start to
eat away the metal parts. Also if they are allowed to build up they
can eventually get to the circuit board and cause shorts. When cleaning
the unit DON’T ever put it under water (running or otherwise). The
sonics are not sealed and when water gets inside it will get to the
circuit. The lack of wiping the unit down daily is the cause of the
majority of sonics failing. This is an accumulated problem. It
happens over a period of time not right away.

When running the cleaner be sure the liquid is at the proper level.
If the unit is heated this means not less than 1" below the rim of the
tank. The heating elements are placed on the side of the tanks and on
smaller units (less than 1 gal.) the heating elements normally are
about 1" down from the rim. The heating elements are designed to
produce a significant amount of heat for their size and without the
solution covering them they will burn out. If your unit is not heated
the same liquid level is suggested however it is not as critical. The
level could go down an inch or so before you endanger the transducers.

The type of solution you use can cause problems for your ultrasonic.
Water with a very little amount of soap is the recommended solution.
Unless you have specifically purchased a unit from the mfg. that is
made for ammonia or other degreasers do not use them. The sonics that
are sold in the jewelry and dental industries are not made for it and
when placing ammonia in one, the cleaner will change it into a mild
acid. Also some manufacturers have found that ammonia and red rouge
for some reason will attack the circuit. The last time I talked with
them they still had not figured out what was happening.

The tank being metal will wear out with use on all units. When the
transducers are working the electrical pulses force them to physically
change shape. This shape changing is what creates the ultrasound. When
the transducers change shape this motion is transmitted to and through
the tank. Imagine taking a piece of sterling flat stock that is 1/2
hard and bending it back and forth many times. What happens? There will
be a line where the metal gets progressively weaker until it breaks.
Just before breaking it will have developed very tiny holes in that
weak area. This is the exact same thing that is happening to your sonic
tank. All of the smaller sonics use tanks that have been drawn down. So
the weakest and thinnest points are the corners. These are the places
normally that will form tiny holes first. Some cleaners operate at
frequencies that will cause the tank to deteriorate where the
transducers are mounted. The more aggressive the cleaner is the
faster these holes will be created.

One manufacturer claims that in their unit if metal filings are left
on the bottom of the tank this too will increase the speed of tank
deterioration. This mfg. makes one of the most aggressive ultrasonic
cleaners on the market.

When running your cleaner don’t let anything rest on the bottom
unless it is plastic or rubber. Again if metal is placed on the bottom
of the tank the vibration will eventually rub a hole in the tank. On an
ultrasonic the last thing you want to replace is the tank. The reason
is that you can’t just replace the tank. The transducers have to be
replaced as well. They cannot be salvaged. So if you have a basket that
sits on the bottom of the tank rather than being suspended make sure
it has plastic or rubber feet on it. These baskets are not ideal for
other reasons as well. Anything that sits on the bottom of the tank
will reduce the ultrasonic activity. It dampens the ability of the
transducers to move the tank bottom. The best way to clean parts is to
suspend them. There are many ways to do this. A basket that uses the
rim of the tank for support, a suspended beaker or a wire (insulated).

Again when using any metal object in the cleaner be sure the unit is
off before removing it or use some kind of electrically insulated
covering on your hands to remove it. I have never gotten shocked this
way but I have gotten shocked from transducers. Transducers can create
a large electrical charge from being heated and cooled, by striking
them or applying pressure. They hold the charge for a very long time if
not discharged and when replacing them it is easy to get shocked from
them a couple of times. Believe me when I say it will only happen a
couple of times! After that you have a fear of being shocked so strong
that you can block out a nuclear explosion if it was set off right next
to you! A shock from the cleaner while it is running is much worse.

Always make sure the ground prong on the plug is in good shape. Don’t
remove it. It needs to be there for safety. If your outlet doesn’t
accept a 3 prong plug change the outlet.

When adding soap to the water in the tank it is better to have too
little than too much. The first and most important job of the soap is
to reduce surface tension so the water will degauss. Remember any
trapped gas in the solution will hinder the sonics ability to work at
top efficiency. After degassing the soap will have some ability to help
clean. However too much soap will reduce the effectiveness of the
ultrasonic activity. The ultrasonic action uses the molecules in the
solution to clean or tear the dirt off the item by stretching them and
them collapsing them rapidly. So any trapped gases will act as a
cushion and will not allow the ultrasonic to work as well as it should.
Think of it this way. If you took a hammer to a ball what happens? The
hammer will slightly collapse the ball and the hammer will be bounced
off of it but the majority of the force will be absorbed by the ball.
The ball in this case is gas in the solution and the hammer is the
ultrasonic waves. All soaps for any purpose have as one of the very
fist ingredients a wetting agent. This allows the water to become
wetter and reduce surface tension. In our use this allows the gasses to
be expelled quickly. Try this experiment: Empty your cleaner. Rinse it
and place fresh tap water in it. Turn it on. You will see some of the
gasses come to the surface. If you let it run for several hours the
majority of the remaining gasses will come out. But instead place a
drop or two of soap in the water while it is running. Within a few
minutes you will see a large amount of gas coming out.

This gas that is released is released because the surface tension has
been reduced. If you were to try and clean a part without the use of
soap you would find it takes a very long time. This is because of high
surface tension. And you don’t want your pieces to be in an ultrasonic
for long. If you remember my last post with the aluminum foil. The
ultrasonic can do this same thing to your pieces if left in too long.

As far as heating for silver. I can’t understand why not. Unless
someone is using some chemical that would cause a reaction. It may have
to do with the fact that they didn’t rinse the soap off the parts after
cleaning and when it cooled it tarnished. But if you use water and soap
then rinse you shouldn’t have a problem. The heat will help loosen and
greases or oils on the piece.

I hope this helps. Take care.

Ken Kotoski
MPG Repair
www.mpgrepair.com


#9
   ... it struck me that you weren't familiar with the molecular
process that annealing brings about... 

And I must admit that YOUR letter strikes me the same way… read
on…

 . when the material is work hardened (to you stiff and non-pliable
) the molecules in the metal have been flattened out to an oval
shape. 

No. Not the molecules. Metal atoms are not actually arranged in
traditional molecules (small structures of a few atoms, which then
behave as distinct entities different from the individual atoms. They
form crystals made of individual atoms. These are arrangements of
many many atoms in a specific ordered structure. Crystals are not
molecules. Work hardening does not form oval crystals or molecules.
The normal annealed structure of the crystals is somewhat random in
shape, but generally blocky shapes, consistant with what a cubic
system mineral structure will form. When metal is worked, the
crystals atoms “slip” along planes of weakness, much like a deck of
cards can be distorted, sliding it to the side to create a skewed
deck. Because of the high symmetry of cubic crystals (virtually all
the metals we work with crystalize in the cubic system), there are
many such possible directions of atomic slip planes, so the crystals
can be apparently flattened or stretched or otherwise distorted in
many ways, depending upon the forces applied in working the metal. It
can be just flattened in all directions, or along a linear direction,
creating elongated flattened crystals, or, such as when drawing wire,
the distorted crystal can become very thread-like in shape. The
hardening of the metal is due to the fact that there are finite limits
as to how far the crystals can distort, especially due to the fact
that the boundaries between adjacent crystals are much less able to
distort than are the crystals themselves.

  by heating the metal up you release the tension created by working
tha metal and the molecules return to a more naturally rounded
state. 

Again, not quite. heating allows the the atoms in the distorted
metal crystals to become sufficiently mobile that they can
recrystalize. What happens is that the large distorted crystals break
down into multiple undistorted crystals. Part of what happens is this
reforming into new crystals, but equally key is that when this
happens, the boundaries between the crystals is redefined around the
new crystal shapes. The new boundaries are unstressed, which is a
large part of why the metal is again soft.

    this holds for all non - feruos metals . material that is
ferrous (steel  etc.  etc.) requires a slow cool. down to maintain
the malability cooling in liqiud would make that brittle! 

It also holds true for ferrous metals, except that with ferrous
metals, there is the added complexity (and this is partly true for
some non ferrous metals as well), that there are a number of different
types of crystal structures than can exist in ferrous metals. Some
are inherently soft and malleable, while others, especially those that
exist at higher temperatures, are hard and brittle. Quenching a
ferrous metal that has been heated high enough for it’s crytstal
structure to reform (annealing temp) freezes the structure of the
metal in that high temp structure, thus maintaining the hardness
(resistance to deformation) that this structure exhibits. If such
metals are slow cooled, then as it cools, the structure reforms as it
passes to lower temperatures, to the form that is then most stable at
those lower temperatures. That lower temp form happens to be soft
and malleable.

   a rule of thumb i've always used as was taught to me is that when
copper silver brass etc. etc. reaches a dull red it is annealed 

True enough, and an easy method to use in practice.

   . the only advantage to plunging the piece into liquid would be
if you were pickling it in acid . this can be dangerous because of
boiling and splatters but it tends to make the pickle take a fast
bite and clean the piece that much quicker. of course there is a
side issue of flex and distortion but that is usually minor. as for
even alloying the materiel so long as it is completely melted mixes
evenly only in a partial melt will you get unmixed allos not to easy
to do. 

quenching after annealing is often needed to get maximum softness in
many precious metals. Sterling silver, and many of the copper rich
gold alloys will at least partially re-harden if slowly cooled. In
fact, heating to just below the annealing temperature and holding it
there for a while (like a half hour), and then quenching can give
silver a half hard temper even if it was fully annealed before. some
rose/red golds can be hardened to a higher hardness through this
process (called precipitation hardening) than you can get with just
work hardening. What happens is that in annealing, all the copper in
the alloy becomes completely dissolved in the greater amount of
silver. But at room temperatures, copper is not as soluable in
silver, and if the sterling is slowly cooled, some of the copper will
migrate to the boundaries of the crystals, forming copper crystals
along thos boundaries. This makes the boundaries of the crystals much
less able to distort than they would otherwise be, and the sterling
will be harder than it would have been if quenched from a higher
temp. You have to be careful not to quench from too high a temp,
though, or you can crack the silver. For that same reason, white
golds and rose golds are best quenched in alcohol, not water, which
chills them fast enough to prevent hardening, but not so fast as to
shock them into cracking. Pure metals, like fine silver, fine gold,
or pure copper, or alloys of just gold and silver (which are
completely intersoluable in each other), are not prone to
age/precipitation hardening, so they can be either slow cooled or
quenched, as you prefer. Makes no difference.

And keep in mind that much of the above discussion is somewhat
simplified, even so. the metalurgy of the alloys we use can get
somewhat complex. For example, sterling silver is NOT a simple mix of
silver and copper crystals, nor is a bunch of crystals with the single
formula of 7.5 % copper that the whole of sterling silver exhibits.
Instead, it’s normal structure, if fully annealed and not age
hardened, is a mix of two different types of crystals. some of them
are pure silver. The others, are silver with 28.1% copper. This
latter is known as the eutectic alloy of silver and copper, and
represents the ratio of the two metals with the lowest melting point.
When molten sterling silver is allowed to cool, at temps above 1435
F, only pure silver crystalizes out, thus increasing the copper
concentration of the remaining molten mass. That concentration will
reach 28.1 percent when the temperature has fallen to 1435, and the
formation of pure silver crystals will stop, as all the remaining
mass now forms crystals of the eutectic alloy. But at room
temperatures, copper is much less soluable in silver than at this
higher temp. At room temperatures, the copper is imobilized in the
alloy. However, at a temp of about 700 degrees, the copper is
sufficiently mobile that it can migrate around, and since the crystals
are more stable will less copper, the copper leaves, reforming
crystals of mostly copper along crystal boundaries, while the
remaining silver crystal will retain only about 2% of the copper…

And sterling silver is just a binary (two metal ) alloy. What
happens in many gold alloys gets even more convoluted.

Understanding these relationships is not, of course, always needed
for what we do in the making of jewelry. But it can help a lot when
you run into problems, or need to solve a problem. Consider, for
example, what Steve Kretchmer has managed to achieve with heat
treatable platinum alloys in order to make his tension set rings
practical. Or consider what you might need to do in casting rose
golds, to ensure that the finished casting is workable and not all
cracky and brittle…

Hope this helps.

Peter Rowe