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All Cracked Up


#1

Hi Everyone, A while back I posted a querry regarding ingot and
sheet making. Recieved a whole bunch of very usefull info and now
I’m able to produce fine sheet and wire in gold----thankyou very
much.

Now I’m stuck and all I have to show for it is crack§y sheet
and wire and a sore back. I’m using .950 silver (thought it
should be easier than .925) and start rolling (in one direction
only) and the cracks appear after a few passes through the
mill. I’m pouring the ingot, straight from the crucible ( which
is clean{ looking} that I melt De-ox alloys in also) where I just
alloyed the pure silver and pure copper, into the heated mold. Am
I contaminating my metal by using a crucible which is used for
De-ox alloys? Should I not pour the ingot directly from alloying?
Does .950 silver not roll well? Am I not getting the melt hot
enough and is there a visual clue to see that? Am I right in the
mold temperature being 400 F? And yes I am sooting the mold
before I pour.

Also, could you please recommend a good book on basic metallurgy
intended for precious metal users and abusers?

Thankyou for your reply, Peter Slone


#2

Peter Hello again! In regards to mold temperature I’ve heard 500
degrees. Just suspend your brand new horizontal ingot mold
between two fire bricks ( or whatever) and position your
crucible below to heat the mold above during melting.

		That does it!
		Tim

#3

Hi Peter

I can think of a couple of potential causes for the problem of
cracs in the rolled 950 silver: 1) Are you using copper or
pennies to alloy? Pennies are often bronze, and most recently
copper plated aluminum I think. This could mess with your
results. 2) If you reduce the metal volume by more than 50%
without annealing you could develope cracks.

Hope this helps
Tom Tietze 'Opals of the Sea’
www.abalonepearls.com


#4

I guess I did not read well enough and I see that you do heat
your mold, so again we are back to the anneal, when I roll large
pieces sometimes I only get 2 passes before I have to anneal,
when you start you are moving a large mass off unconstricted
material and it will seek the softer areas first, as you
compress the metal is still in large crystalline form, it takes
repeated molecular action and compression to bring the metal to
consistency, hope that explains. … Ringman John


#5

Hey Pete are you annealing your metal? It sounds like perhaps it
is cooling to fast as an ingot, do you heat your ingot maker? My
experience says if the metal cracks you are subjecting it to
work hardening, as you sheet metal you must anneal frequently
until the metal gets to about 25 gauge, then you must still
anneal every 5 gauges. I hope I have helped, by the way heat
until cherry red with an alcohol borax solution on the metal (to
prevent firescale) and quench as the metal goes to very dull red
in cool water. … Ringman


#6

Hello Peter!

The problems you are having sound familiar. Occasionally
this can happen when rolling any metal especially white gold!
The number one problem is overheating the metal when pouring the
ingot. This can cause molecular damage to the alloyed metals.
Through trial and error you should be able to reduce your
temperature (a reducing or neutral flameonly; oxidizing flame -
big no - no!) to a minimum temperature and still fill your ingot
mold. Years back I switched to a horizontal ingot mold; it is
easier to keep the temperature down.

The culprit could be contamination in the refining process.
The common contaminant is tin and occasionally lead. If either
is present during the process of refinement the metal will not
roll. I had tin contamination in some 14k several years ago. I
was told the tin comes from the addition of fluoride to our
water supply, (please don’t start!) and must be purified
routinely (deionized, etc.) prior to using the water in the
refinement of metals.

If you get a line on a (written for layman jewelers) metallurgy
book I would be very interested! This is an area jewelers are
commonly uninformed. (sorry folks!) We know what the metal does
and does’nt do. But we don’t know why! Not very sensible when we
try to stretch the parameters when working with metals.

Good luck!

		  Tim

#7

And while we’re on this great new “tips” thread-- does anyone
have a good tip on how to pour that big shiny blob of hot metal
down that teeny little hole in the vertical ingot mold?

            Thanks, Peter Slone

#8

A while back I was having a lot of trouble with gold ingots
cracking into a thousand tiny fissures. I never really figured
out the problem since it was all totally new metal. Any
suggestions?

Alan Revere
Revere Academy of Jewelry Arts
San Francisco


#9

I use rainwater from the rainbarrel to use in my shop, this has
been filtered and settled for months, then I have a safe water,
(no chlorine or fluoride or contamination from old pipes) thanks
for Seattle rains, I have found this to be a suitable water and
it works well, Just get it before the summer bugs live in it,
who knows what they leave! … Ringman John


#10

Hi Peter Slone, Personally, I think you heat to much your metal.
This problem happen often at school. By the moment the metal is
forming as a drop and when it’s start to roll on itself you must
pour it. Don’t worry about mold temperature. After 25 years of
making ingots almost each day and looking students doing their
own at each day, we do not preheat molds before, may be to take
off humidity (problem we don’t have here). Even if it sounds
unusual, I frequently change student’s ingot mold for a cold one
when they are close to cry after many try. To be sure you can
also anneal your ingots before rolling them. Don’t forget to
apply oil on the surface of the mold. Vincent Guy Audette


#11

Peter,

You should use a different crucible for every alloy you are

working with. Many lower karat gold casting alloys and some of
the no tarnish “sterling” alloys are alloyed with silicon. It
can cause the cracking you are talking about. The other thing to
watch out for is overheating the silver when annealing and then
quenching it too hot. Silver copper alloys tend to be “hot
short” i.e. they cannot (or should not) be forged hot as they
will crack or crumble. The thermal shock from quenching silver
that is too hot will also crack the silver .

Another thing to try is to  only make very small reductions  on

each pass throught the mill and anneal more often in the early
stages of the rolling process. This will reduce the strain ol
thevery weak crystal structure that is formed by the large as
cast crystals.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-436-3552


#12

I would think the ingot was not hot enough, or the metal lost to
much temp in the pour, gold will crystallize if poured to
cold… Ringman John


#13

Peter,

Isn't that fun? Try putting the C clamp at a height which will

balance the bottom of the crucible. When the metal then is molten
you can just tip it up and pour it right in the end small hole.
Good Luck! Russ


#14

And while we’re on this great new “tips” thread-- does anyone
have a good tip on how to pour that big shiny blob of hot metal
down that teeny little hole in the vertical ingot mold?

Grind a V groove into the lip of your crucible to channel the
molten metal.

Alan Rathbone


#15

In other metals, it’s often good to hammer with a plannishing
style (many, many rapid light hits, consistently over the entire
surface) and anneal frequently, to decrease the grain size of the
metal. Then go ahead and roll your metal, with frequent
annealing. As you may have noticed I’ve learned the hard way, if
in doubt, anneal, anneal, anneal! I don’t know if there is an
"normalizing" procedure for silver alloys as for tool steels? Any
one know??
Hope this and other notes provide the solution for you, let us know. efw


#16
   And while we're on this great new "tips" thread-- does
anyone have a good tip on how to pour that big shiny blob of
hot metal down that teeny little hole in the vertical ingot
mold? 

… Carefully…

Actually, two thoughts. Set up the mold so the clamp is
positioned such that you can rest the bottom of the crucible on
it just before pouring, so that you mostly just have to tip the
crucible to pour. It will help you be in the right place. Also,
part of the problem is simply seeing where to pour. The glare
that makes that hard is often mostly sodium flare, giving you
lots of bright yellow flame… If you borrow a glassblowers
tool, you can eliminate that glare. I’m referring to glasses
made with what’s called rose didydium lenses. These filter the
sodium flare. There’s a higher grade of the same, that’s also
better color balanced too, called AUR-92. It’s also more
expensive than the dydidium type (which isn’t exactly free
either) While both types of these lenses may seem to be
extravegantly costly to those who’ve not used them, they make a
dramatic difference in your ability to see through the normally
bright yellow flare one gets when the flame hits flux, borax,
boric acid, or other sodium containing compounds. We’ve found
these to be quite useful for melting metal in casting, pouring
ingots, etc. And for many delicate soldering operations, I’ve
found them to be almost indispensible. Not quite sure how I
managed without them in my younger days (actually, I do know
how. My eyes were better, and I squinted… But I still wish
I’d had these a long time ago.

For those wishing more info on these types of glasses, check out
http://www.auralens.com/public_html/glass.htm

Hope this helps.

Peter Rowe


#17

Hi Peter

I had problems with my ingots cracking and was told to get as
much reduction as possible each time through the mill. This
forces the metal to compress evenly throughout the entire
thickness. To little reduction only moves the outside molecules
leaving the center not moving as much, whick causes fractures.
Hope this helps, it cured most of my problems.

Bill Wismar


#18

I would think that the gold was possibly contaminated. I had
this same problem one time when I was doing my own refining. I
was using sulfur dioxide gas to precipitate the gold from the
acid solution and I didn’t get the “mud” rinsed well. I believe
traces of the acids and sulfur dioxide gas contaminated the gold
making it totally useless. Possibly you received a batch of bad
gold or the crucible was contaminated with something. I know
silicon containing golds do not roll well, but I wouldn’t see
any reason they would crack upon pouring into an ingot. Just my
thoughts. Ken Sanders


#19

Some casters have complained about the same type of problem.
They say it like the metal looks like a cob web of
crystalization. The solution I found was to check what kind of
metal you use and make sure you melt appropriately. The deox
metals need to be melted at a much higher temperatur than the
traditional Handy Harmon melting temperatures. The other answer
may be contaminated copper in your alloy. Pure copper has all
the arsenic removed. If there is any arsenic in cheap or non
pure copper you can have some bad castings or pouring problems.
You never know about this until you have these problems. I have
seen this in some gold from the far east. New pennies are mostly
zinc and can also create a great alloying problem.