Hi,
I have an amazing amount of scrape silver and I don’t do any casting.
I wanted to get some on how to go about melting down the
silver, what shape to cast it into, and what kind of form (mold) to use,
and tips on rolling it out into plate and wire. I already own the rolling
mill.
none of my books cover this problem. Any help would be appreciated.
erica
I wanted to get some on how to go about melting down the
silver, what shape to cast it into, and what kind of form (mold) to use,
and tips on rolling it out into plate and wire. I already own the rolling
mill.
Hi Erica, What we did when I was an apprentice was the following way: we put
the silver filings and scrap into some sort of iron vessel (I have used
lids of sweets boxes) and put it over a gas flame (Bunsen burner, torch
with soft flame) to anneal it, so burning away dirt. The silver should
come to red heat. When cooled, we spread the metal on a sheet of plastic,
added borax or any flux (powder) and kind of stirred it with a magnet to
get any iron/steel out of it. Then into the crucible. When melting, start
heating from below as not to blow up the filings into the workshop, you
could also wrap the metal in - well, I don’t know the English word, it’s
some kind of very thin, translucent paper - and soak it with a liquid
flux. As a mold, best is an iron one, mine is just two L-shaped thick
pieces with the short leg 4mm (13/32"), one of them srewed to a base
plate, the other one clamped against it. The short legs of the L give the
thickness, 4mm, the width of the ingot determined by how far apart the
legs are clamped together. I always skew the mold by standing it onto a
scrap piece of iron, so any gases can get to the surface of the silver in
a short way, and don’t need to travel through the whole length, getting
trapped by the solidifying metal. You’ll not be very pleased to detect it
afterwards. A good idea is to cover the mold inside with soot by holding
the parts over a flame before clamping together, to reduce oxidation and
to get a better surface on the silver. You could use some specially
formulated flux like Argoflux or Auropurifax to help in getting a clean
casting, ask your supplier. For rolling, dont change the direction you feed
the metal to the mill without previous annealing and quenching, as this
would result in splits. Cover the silver with borax when annealing to
prevent subsurface oxidation. The latter is a real nuisance as there is no
remedy, there will be scale (a bluish shadow) and sometimes the surface of
the silver gets pitted during polishing. Annealing can be done after about
75% cold working the silver; too often, and you get orange skin and the
metal is likely to break when bending, as the crystals grow too large. Hope
this will be of some help, it has worked for me the last dozen years.
Markus
I wanted to get some on how to go about melting down the
silver, what shape to cast it into, and what kind of form (mold) to use,
and tips on rolling it out into plate and wire. I already own the rolling
mill.
Erica
#1 To melt the silver use a reducing flame. That is a flame with a slightly
bushy tip at the end. This is acheived by using a little more fuel than
normal, and a little less Oxygen. The reason for this is so that the flame
is starved for Oxygen and will not impart any extra Oxygen into the metal
when it is molten than is necessary. This is a major cause of porosity in
silver. Silver can actually absorb up to 12 times it’s volume in oxygen
,Sulpher and Hydrogen when in it’s molten state in some cases.
#2 The shape to cast it into depends upon the final use to which you will
put the metal. If you want wire pour it into rods, if you want sheet pour
it into a flat plate, if you are going to raise it into a form, a thick
ingot wire will be of more use. Or you can cast it into an item that is
marketable.
#3 The type of form or mold can be bought or built. Many tool supply houses
have very nice ingot molds in various sizes. Make sure to get one that is
not for white metal. These are for low temp. metals and silver will
actually fuse to the mold creating a very nice paper weight. To make one
all you need is sheet steel about 1/8 inch thick. Braze or wield the steel
into the form you want to create your own mold. Make sure all of your edges
fit tight so you will not get any leaks. Also on more elaborate molds stay
away from undercutting as the item will not release. In most steel molds or
iron molds the surface needs to be smooth and coated to help with the pour.
One trick is to use the carbon suit from an acetlyene torch to coat the
surface of the ingot area. Another way is to coat the surface with oil
before bringing the mold up to temp. This will burn away leaving a nice
coating of carbon. And it does help to pre heat the ingot mold. If you do
not the metal will cool to rapidly as it is being poured. This causes
layers to form in the cast ingot as the first part already in the mold is
solid while you are still pouring into it at the top. These layers can
seperate when work hardened. A mold temp of around 750 to 850 is fine.
#4 Tips on rolling out metal. Everyone has their favorite ways and there is
no one right way. Whatever works for you is fine. Here are a few of my
ideas. Sterling silver will work harden easily. The copper alloy is the
cause of this. To prevent cracking frequently anneal the metal. Once again
use a reducing flame in a low light situation. Dip the silver in a boric
acid solution. This will act as a barrier to the atmosphere and prevent the
silver from absorbing any unwanted gases. Heat the ingot from the edges not
the middle. The ingot will loose most of it’s heat by radiating it from the
edges. Bring the entire ingot up to a dull red in color and hold there for
at least 60 seconds. Try not to get the item to hot or reticulate the
surface. That is why I use low lighting it is easier to see the colors. Now
it is time to cool the ingot down. The slower the cooling period the better
in my opinion. The metal will form a grain or crystal structure depending
upon it’s cooling cycle. If you quench the ingot the crystels formed are
small and tightly packed. We need larger crystal structures that are
loosely spaced. This is acheived by allowing the metal to air cool for a
few minits. After a certain temp the process has stopped and further
waiting is not necessary. As a general rule if it does not cause quenching
liquid to spater it is cool enough to quench. I use alcohol to quench in.
It has less free hydrogen and oxygen to be absorbed into the metal and
offers a slower cooling rate. It also will not leave mineral deposits on
your metal. To roll out the metal always roll the ingot in the same
direction. This causes that crystaline grain structure to be pulled in one
direction. If you go in several different directions the grain strusture
will be pulled in several directions as well and will lend itself to
cracking much more easily. I roll my metal until it starts to get stiff.
about 1/2 to 3/4 turn of the roller adjusting wheel. If you do get a crack
started drill a hole right in front of the crack This will releive some
stress and when the crack reaches the hole it will stop.
Keep your rollers clean
RED
Erica
I first dug out a long shallow hole in charcole. Put the silver scrap into
it and melted it right in there. after it is molten take another piece of
charcole and place it over the molten metal. I usually got it to look like
a very short thick rod. Let it air cool and run it through the mill a
couple of times. Your going to have to anneal it every couple of passes
through the mill. you can make wire, plate, flat wire, half round wire. I
did not use an ingot because I was allways afraid that when you poured the
metal it would splatter. Nick
< The slower the cooling period the better
< in my opinion. The metal will form a grain or crystal structure depending
< upon it’s cooling cycle. If you quench the ingot the crystels formed are
< small and tightly packed. We need larger crystal structures that are
< loosely spaced.
dear red
It has been years since I read Tim McCreight’'s book on metalsmithing, but
I thought I read that because gold and silver are not ‘ferrous’ metals,
they don’t act the same way in regard to their crystalline structures.
Although (please remember this is my memory, not his quoted word) one
doesn’t want to quench red hot, the long cooling period is not necessary as
is in annealing steel. Am I correct??
waterphoto (allan freilich)
Nick If you heat the mold the metal will not splater. It is the same
principal as when you spit into a hot griddle. I once poured metal into a
cold mold that had oil in it. I forgot to heat it. I still have silver in
the ceiling tiles to this day.RED
Nick If you heat the mold the metal will not splater.
Very good point. A byproduct of you r torch is water. That moisture will
condense on any relatively cool piece of metal. As soon as molten metal
hits it, it boils causing the metal to splatter. I always get my metal
molds hot enough to burn olive oil (my favorite mold lubricant).
Nick If you heat the mold the metal will not splater. It is the same principal as when you spit into a hot griddle. I once poured metal into a cold mold that had oil in it. I forgot to heat it. I still have silver in the ceiling tiles to this day.RED
The splattering is caused by moisture, you have to heat the ingot mold
enough to drive off ALL the condensation. A cold mold will simply freeze
the metal. I once poured about an ounce of gold into a non-heated ingot
mold and it seemed to virtually explode. We swept up and all we ever found
was micro sized grains.
Jeffrey Everett
< the long cooling period is not necessary as is in annealing steel. Am I
< correct??
You are correct. The long cooling period associated with ferrous metal is
not needed with non ferrous metals, but you do not want to quench it while
it is still glowing hot. I usually wait until it has cooled down enough so
that it will not cause my quenching liquid to spatter. It is still hot but
has cooled down enough so that any restructuring has stopped. RED
The splattering is caused by moisture, you have to heat the ingot mold enough to drive off ALL the condensation. A cold mold will simply freeze the metal. I once poured about an ounce of gold into a non-heated ingot mold and it seemed to virtually explode. We swept up and all we ever found was micro sized grains.
We have done exactly the same thing years ago when we were pups in the
jewellery business. Why do you never find all the metal? Where does it go?
Also be carefull not to heat up anything hollow without making a hole in it
to let out the air. My apprentice, Colin, started to melt down some scrap
gold. I asked him to wait until I was free to supervise him but he did not.
A ball stud exploded from the bottom of the melt and molten metal was shot
everywhere including Colins eye. It went straight through his safety
glasses. He was off work for for 4 weeks and now has to wear glasses to
correct his sight.
Let this be a warning to everyone.
Andrew