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Reusing sterling sprue bases


#1

I’ve got a growing collection of sterling sprue buttons from prior
castings. I re-use these as I can, mixing them 50/50 by weight with
new sterling casting grain. Most of my castings are small flasks, but
occasionally I use a larger flask which produces a sprue base that’s
too big/heavy to be used “as is” in later casting.

I’m not keen on the idea of spending days and lots of energy cutting
the big sprue bases into smaller parts for more convenient re-use.
Would it work OK if I melted the larger sprue bases down, and poured
them through water to make “sprue grain”, which I would store
separately and mix in the usual 50/50 ratio with new sterling grain
to make new castings? Or would that cause problems with the finished
castings? I’m not sure how many times sterling silver can be melted
without adding new metal.

–Kathy Johnson
Feathered Gems Pet Motif Jewelry
http://www.featheredgems.com


#2
   Would it work OK if I melted the larger sprue bases down, and
poured them through water to make "sprue grain" 

Usually called Casting grain. and yes, that’s how it’s done. Pour
from a bit of a height, and into a deep enough container, or you’ll
find the molten silver still liquid when it hits the bottom of the
container, so instead of sprue buttons, you’ll have one large splashy
melty thing on the bottom of the container… If the water is
stirred/moving, this helps a lot too.

 , which I would store separately and mix in the usual 50/50 ratio
with new sterling grain to make new castings? Or would that cause
problems with the finished castings? I'm not sure how many times
sterling silver can be melted without adding new metal. 

Traditional sterling silver does not have deoxidizers to be
exhausted by repeated meltings. The main concern is simply a build
up of various contaminants and impurities, as well as a gradual
depletion of the copper content. If you’re cleaning the metal well
before melting it down (no investment traces still on the buttons,
for example), pickling the grain and washing it, etc, so that what
you melt down, either from sprues or new metal, is clean bright
grain, then you probably don’t have to worry much at all. If the
silver ever does start to get weird, then while it’s molten, add a
bit of ammonium chloride. (DO this OUTSIDE) and stir. This will help
remove a number of possible contaminants, like iron, base metals,
etc. While the 50% new metal rule of thumb is good practice,
especially with gold alloys that may have deoxidizers, with plain
sterling silver, it’s merely a guide. I’ve got some silver that’s
probably been cast a dozen times or more, with no apparent reduction
in the quality of the castings I get.

Peter


#3

chop them into smaller pieces with a bolt cutter rather than melting
them . works better if you clamp one arm of the bolt cutters into a
heavy bench vise.

Talk to you later Dave


#4

Kathy, The shot you normally buy is made using a shot tower of some
kind which will make nice round bead like shot without any voids
cracks or crevices. If you just pour into water you are likely to
get large lumps and lots of flake like “shot”. You are likely to
trap water in your shot and this will lead to the shot acting like
popcorn when the steam pressure builds up in the voids during
melting. It also will be highly oxidized by the melting and pouring
into the water so if you try to clean this up with pickle you are
unlikely to get all the pickle out of the crevices and voids in the
"shot" this will lead to contamination of the silver as it is melted
causing porosity in the castings. You are better off pouring into
long wire molds which are ingot molds that make 1/4" or 3/8" square
x 8" long bars for rolling into wire. These can be easily cut with a
heavy duty shear and added to your melt. They are easy to pickle and
will not trap water or pickle in them. If you like the molds are
easy to make by having someone weld a couple of end plates on a 8"
piece of 1" angle iron so that it is positioned like a “V” trough
with end caps.

Also if you recycle sprues it is very important to get all
investment off the sprues before re-melting. The investment when
heated to the melting point of sterling will break down and produce
sulfur dioxide gas which the silver will absorb and will result in
gas porosity every time you cast with this contaminated metal. It
cannot be removed from the silver by anything short of a full
refining of the silver. This little housekeeping issue is the main
reason that recycling sprues is not the best thing to do. It is
very hard to get all the investment off the trees. So each time you
recycle your metal you are raising the contamination level and
reducing the surface quality of your castings. So if you are going
to recycle your sprues do your best to remove all investment from
them before reuse

Jim


#5
   I do a less risky thing: sprinkle some borax powder over the
molten silver, this helps clean a little bit (of course, if you
don't have serious "dirt" like other metals... ) 

Boric acid is a fine melting flux, but it’s principal action is to
dissolve oxides, and to form a molten film over the surface that
protects the molten metal from further oxidation. It won’t do
anything to remove or alter contaminants within the metal. Ammonium
chloride, on the other hand, reacts with the more reactive metals,
including zinc, iron, and many others, for form metallic chlorides.
It does this in the order of metal reactivity, so the most reactive,
like zinc, or iron, are converted to chlorides before the less
reactive silver or copper. And the chlorides are not soluble in the
melt, so once formed, the float to the surface and slag off.

As to risk, for the most part, using ammonium chloride isn’t all
that risky, largely because you’re only using a small pinch of the
stuff in a melt. But it nevertheless produces volumes of blue,
smelly, fumes which really are not good to breath. Enough of it will
give you a nasty headache. Sensitive people might react worse than
most. But it’s not like something so toxic that you’ll just keel
over or anything. If you’re ventilation is good enough that
you’re safe in melting your metal in the first place, then in all
probability you’ve got sufficient exhaust to handle the ammonium
chloride produced fumes, too. Of course, that brings up the whole
question of folks melting lots of metal in basement shops without any
decent ventilation…

In normal melting, boric acid is the normal and usual flux used. If
you mix up a flux of half boric acid and half borax powder, you’ll
have a very fine melting/casting flux for silver and gold alloys.
Boric acid and Borax both do the same thing when molten, but the
borax melts, and is active, at lower temperatures than the boric
acid. So the mix starts to protect the metal at a lower temperature,
further reducing chances of oxidation.

Peter


#6

Will I ever learn? This orchid thing is like a drug…

Dear Mr. Rowe, If I understood it correctly, you are recommending
that small jewelry casters add a “pinch” of ammonium chloride onto
their melt under some general overhanging hood that they may use to
evacuate heat or fumes from plating or burnouts in order to remove
contaminants of “zinc, iron, and many others”. You are further
saying that this heat induced decomposition reaction is “isn’t all
that risky”. You are accurate in your statements about ammonium
chloride being relatively safe “in its powder form”. It will also
certainly react with the metals that you described and do what you
said that it would to zinc and iron. I have always found your posts
to be very good, quite clear, accurate, and with the safety of all
in mind. However in your response about the reuse of silver buttons
I feel that you may be answering a different question than the one
that was asked. The following is the data on Powdered Ammonium
Chloride in a jar.

Health Rating: 1 - Slight Flammability Rating: 0 - None Reactivity
Rating: 0 - None Contact Rating: 1 - Slight Lab Protective Equip:
GOGGLES; LAB COAT Storage Color Code: Orange (General Storage)

People should not consider the use of ammonium chloride as a common
step for the reuse of their sterling silver buttons. If your
casting and metal processing system is such that you may have
contaminants of iron and unintentional zinc then you may want to
consider cleaning up your metal processing and casting system first.
Further, if you feel that your sterling metal is contaminated, it
is far safer and potentially cheaper to send your silver scrap off
one of many refiners or metal suppliers that offer trade programs.
Peter, I feel that you are probably more familiar with metallurgy
and chemistry that most and that seems simple and safe
to someone skilled as you are, may be quite unsafe to one more
skilled in other areas.

Heating Ammonium Chloride causes a decomposition reaction and it is
this reaction that people need to be considering. You did make note
of "Of course, that brings up the whole question of folks melting
lots of metal in basement shops without any decent ventilation…"
It certainly does bring this to mind in a great big way. What is
the definition of decent ventilation? Opinions vary. When heated
to the temperatures required for melting sterling scrap, ammonium
chloride (NH4Cl) will liberate ammonia and hydrogen chloride.
Depending on the definition of “pinch”, the ventilation situation of
X jeweler, they could be in for serious trouble.

Ammonia gas at levels as low as 500 ppm (parts per million), will
cause immediate and severe irritation of nose, and throat. Brief
exposure to concentrations above 1500 ppm can cause pulmonary edema,
a potentially fatal accumulation of fluid in the lungs. The symptoms
of pulmonary edema (tightness in the chest and difficulty breathing)
may not develop for 1-24 hours after an exposure. Mixtures of about
16% to 25% (by volume) ammonia gas in air are flammable.

Hydrogen chloride is irritating and corrosive to any tissue it
contacts. Brief exposure to low levels causes throat irritation.
Exposure to higher levels can result in rapid breathing, narrowing
of the bronchioles, blue coloring of the skin, accumulation of fluid
in the lungs, and even death. Exposure to even higher levels can
cause swelling and spasm of the throat and suffocation. Some people
may develop an inflammatory reaction to hydrogen chloride. This
condition is called reactive airways dysfunction syndrome (RADS), a
type of asthma caused by some irritating or corrosive substances.

I would highly recommend that if you do not have a background in
handling that sort of chemical that you stay away from it or get
very informed and hardwared. It is of course ideal to pickle and
clean your scrap before remelting. The use of a 50/50 borax and
boric acid mix should be more than sufficient to remove the lighter
metal oxides and minor residual investment that may have been
imbedded in your buttons and scrap.

This from the makers of 20 Mule Team Borax: Precious metal recovery
Borates readily associate (combine with) with metallic oxide
contaminants at a sufficiently low temperature to minimize the loss
of precious metal and to reduce wear and tear on melting equipment.

Non-ferrous metal production

Borates act as a flux during the smelting operation, dissolving
metallic oxide impurities that are then removed with the slag.
Borates are also used as a cover flux to protect metals against air
oxidation.

Please know Peter that I have great respect for your and
God how I hate the petty one upmanship responses that I see on this
website from time to time. So please know that this response comes
from a man with only 65% of his lung tissue remaining due to a car
accident many years back and is very particular about his lungs. I
have also been in a jewelry cyanide accident that landed me in the
hospital at the ripe old age of 19. To top that off I also had a
very nasty experience from the chlorine gas that was liberated from
a “completely safe”, Salt Refining System (under a hood), that is
still sold in the jewelry industry today. Of course, I am older
and wiser these days. Cough, hack, etc… Others may say that I am
using scare tactics to make a point and my answer to that is, your
damn right I am.

Best Regards with the Best of Intentions,
J. Tyler Teague
JETT Research


#7
   Will I ever learn?  This orchid thing is like a drug... 

(grin… don’t i know it!)

   Dear Mr. Rowe, If I understood it correctly, you are
recommending that small jewelry casters add a "pinch" of ammonium
chloride onto their melt under some general overhanging hood that
they may use to evacuate heat or fumes from plating or burnouts in
order to remove contaminants of "zinc, iron, and many others". 

Well. Not really recommending. As you have amply pointed out, if
such contaminants are there at all, then the overall process needs
review. And, most likely, anyone casting larger amounts will
actually be reusing only cast metal, and these contaminants aren’t
likely a problem. The problem is most likely found with folks
reusing things like scrap silver from fabrication, where small amounts
of silver solder, etc, may be introduced. That’s the most likely, I
think, source of zinc. bits of broken saw blades, file teeth, and
the like, can introduce small amounts of iron. The situation is
most likely to arise, not so much with silver, where it’s low cost
reduces the incidence of people slavishly reusing their scrap, or
needing to correct messed up metal. But for the goldsmiths, an
ounce or so of brittle metal can be a problem. Then the ammonium
chloride can be a real money saver. For most people, this is seldom
a problem, so the situation won’t arise. But when it does, then a
small bit of ammonium chloride can help out, as a refining flux.
This idea, by the way, isn’t one I came up with. It first came to my
attention in a turn of the century book by the (then) eminent author
on precious metals use in Britain, George Gee. He recommended
several such refining fluxes as ways to potentially cure certain
problems of, notably, brittleness in the metal. That applies to both
gold and silver alloys. Obviously, he was writing at a time when
authors did not have to assume all their readers were untrained or
idiots. I would like to also assume that though many orchid readers
may be less experienced, few are idiots. And her in orchid, there’s
always the safety valve. If someone like me writes something that
some other reader feels understates the safety aspects, no doubt
there will be follow up articles to correct the oversight, for which
I thank you sir.

But I stress that this is NOT normal and frequent procedure, and
certainly not a routine thing to do. If you’ll reread my original
mention of this, I wrote in large capital letters that this should be
done outside. Equivalent ventilation with a good hood might also
suffice. As you note, anyone doing this regularly will quickly find
the process quite noxious if they don’t have proper ventilation.
And of course, a “pinch” is just that. A tiny amount. Again, if
anyone mistakes this word, and dumps in a whole bunch of the stuff,
they’ll quickly find themselves rushing around opening windows and
leaving the area. I DID say the fumes were nasty, didn’t I?

     However in your response about the reuse of silver buttons I
feel that you may be answering a different question than the one
that was asked. 

I may have strayed a bit, yes.

The following is the data on Powdered Ammonium Chloride in a jar. 

46or the record, the little jar of ammonium chloride that I use
comes from a children type chemistry set supply. I didn’t buy the
whole set. Just the refill jar at a hobby shop. That suggests that
at least a few folks aren’t much alarmed by the stuff in that form,
as it’s sold for use by the least informed chemists possible…

   People should not consider the use of ammonium chloride as a
common step for the reuse of their sterling silver buttons.  If
your casting and metal processing system is such that you may have
contaminants of iron and unintentional zinc then you may want to
consider cleaning up your metal processing and casting system
first. 

Agreed. But if you find yourself in a situation where you MUST
reuse some questionable scrap including some blobs of solder,
perhaps, then, well, perhaps this method is a useful one to remember.
Normal casting buttons need only a good pickling to remove oxides,
and a very good cleaning to remove all traces of investment.

 The use of a 50/50 borax and boric acid mix should be more than
sufficient to remove the lighter metal oxides and minor residual
investment that may have been imbedded in your buttons and scrap. 

Agreed. That mix is my preferred casting/melting flux. I’d stress,
as someone already did, (Jim Binnion, I think) that removal of traces
of investment make a big difference, as traces of that break down
into sulphur compounds that cause significant problems with the
metal, and unlike oxides that slag off to the surface with the
boric/borax flux, can remain in the metal.

       Please know Peter that I have great respect for your
and God how I hate the petty one upmanship responses
that I see on this website from time to time.  So please know that
this response comes from a man with only 65% of his lung tissue
remaining due to a car accident many years back and is very
particular about his lungs.  I have also been in a jewelry cyanide
accident that landed me in the hospital at the ripe old age of 19.
To top that off I also had a very nasty experience from the
chlorine gas that was liberated from a "completely safe", Salt
Refining System (under a hood), that is still sold in the jewelry
industry today.   Of course, I am older and wiser these days.
Cough, hack, etc...  Others may say that I am using scare tactics
to make a point and my answer to that is, your damn right I am. 

Well, right you are to be concerned with your own health, and that
of others. Scare tactics are not a bad thing, when used with accurate
info, which your’s generally has been. thanks for bringing to my,
and the groups, attention, any impression that my little trick might
be considered routine, or cavalier. Hmm. I wonder if it’s not then
such a good idea to note that when one’s cyanide based gold plating
solutions are starting to give a somewhat paler color, that it may be
due to not enough free cyanide, and a pinch of sodium or potassium
cyanide added to the bath might considerably improve the color? Hmm.
No, I better not mention cyanides at all, I guess.

Best Regards with the Best of Intentions. 

Likewise, with thanks.

Peter


#8

BRAVO TYLER!!! I could not have stated anything as well. Not in a
million years! (Nor do I know that much technical language).

A simple solution I switched to several years ago is to cast only
with the Deox sterling silver. I have many many times cast only sprus
with this silver and had perfect castings. I know this is not the
perfect way, but for me and many it is the ECONOMIC way. In fact I
prefer to cast mostly sprus when in production. The ratio is usually
70% spru and 30% new. Just make sure all the investment is cleaned
off the spru buttons. I do this by pickle, ultrasonic, steaming and
scrubbing until they are all clean. Kind of the old fashioned way.

I started casting back in 1971 and have seen and done it all. My
bottom line is pit free Sterling Silver finished jewelry in hand
without a lot of screwing around. If anyone wants my silver source I
use exclusively Stebgo Metals (651-451-8888) casting deox for all my
silver product. Their gold casting grain is tops also.

Keep up the great comments Tyler.

Best Regards,
Todd Hawkinson