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Lost wax casting 101


#1

Hi

My name is Adam, I’m trying to make an engagement ring for my
girlfriend using the lost wax casting method. I’ve finished making
the wax model and am about to embark upon actually casting it. I am
well out of my depth and comfort zone but loving every second!! I
have some questions (probably very basic but can’t find the answer on
the site) I hope people can help me with.

I’m trying to do this on a very tight budget as best I can!!

1.) I don’t have access to a bell jar and vacuum pump etc. so am
using a (cheap) hand vacuum pump to pump the air our of an old
airtight jar - how much of a vacuum do I need to produce to get all
of the bubbles of of the plaster??

2.) How hot do I have to cook the cast so I know all the wax is
gone?

3.) I’m using a plumber’s blowtorch to melt the gold (an old family
heirloom of a gold chain) - can I heat it too much? How do I know
the temperature is right? Can a plumber’s blowtorch get hot enough?

4.) I don’t have access to a ‘proper’ centrifuge and am in the
process of making one using an old router. I’ve got some delft clay
to make our wedding rings which instructs just to pour the molten
gold in (it uses air holes so the gold moves down) why do we have to
centrifuge for lost wax casting? Can I not just pour it in?

I have a few more questions but they are the big burning ones that
I’m struggling with!!

It’s really important that I do this myself and so I don’t really
want to go to a professional as I feel it will take away some of the
magic with the ring. Any advice you can give would be great

Sincere and prolific thanks for your help in advance!!

Adam


#2

Hi Adam,

Errr…I’ll try to put this all gently, but focus on the wax ring.
Get that exactly the way you want it, then send it out for casting.
There are plenty of firms in the UK that specialize in job casting.
Trying to wing it yourself with the gear you’ve mentioned is a
recipe for disaster on a wedding ring. If you had more time, and
more chances to experiment, you could use those to learn and refine
your technique. Trying to go from a standing start right into a
wedding ring straight out of the gate isn’t likely to end in
anything but very expensive gold tears.

I’ll take your points in order, but trust me on this one: look for a
job caster. It’ll still be your ring, you’ll have to do all the
finishing, but they’ll do the bit you don’t have the kit for. Much
safer and more likely to work.

I know you want to do it all yourself, but many of us on Orchid have
seen this movie before. You’re not the first to try this. It doesn’t
end well.

  1. no vacuum chamber. Can be overcome (more or less) by intense
    vibration of the flask for a minute or two after you pour it. You’ll
    have to build some sort of a vibrating table rig, but this can be
    done. You’ll still likely have air bubbles, but probably not enough
    to junk the ring.

  2. roughly 670-700 degrees centigrade. Well beyond anything an oven
    can do. You’re talking kiln here. That’s max temp to make sure the
    carbon’s gone. Final casting temp should be around 510-525 C. Still
    well out of oven range, and it needs to be brought up gradually over
    a couple of hours. Not something you’re going to do with bricks and
    a blowtorch. (I think in Fahrenheit, so those values are ballpark.)

  3. plumber’s blowtorch. Depends on what you mean by a plumber’s
    torch, but the probable answer is no.

If you’re talking about one of those torches where a torch tip
screws right onto a tank of compressed fuel, then no, you can’t do
much more than melt little rings of your chain. You might be able to
get bits of it molten, but probably not the whole thing, all at
once. By the by, what do you plan to melt the gold in? You’ll need a
crucible and flux, as well as a more powerful torch. (As well as
more gold than you think you’ll need. There are sprues to fill too.
And chains tend to have all sorts of nasty things mixed in with them
that mean that they tend not to cast well when remelted…) (they’re
still the right karat, but they tend to have solder built into the
wire itself to make it easy to solder them together. The solder
fouls the alloy for casting.)

  1. Do NOT use a router to power a centrifuge unless you find some
    way to gear it WAY down!

Better thought: just don’t use a motor. Period. Way too fast, and
likely to tear itself apart.explosively.

Most small centrifuges are spring powered. They start off pretty
quick, but then coast and spin down after the spring uncoils. Max
RPM is probably somewhere well below 300 rpm, even at launch.
Balance is a real issue with pounds of flask and metal spinning
around like that. Get the balance wrong, and the best thing that
happens is that it lurches around the room like a drunk washing
machine. Don’t ask about the worst case.

There are motor powered ones, but they’re big industrial units,
built by people who know what they’re up to, with serious interlocks
and blast shields to prevent or contain catastrophic failures. It
should tell you something that the real ones all come with blast
shields to contain the inevitable shattered molds and flying bits of
molten metal.

Absent a real centrifuge, there are better ways to do lost wax:
steam casting comes to mind. Much safer, with almost no kit needed.
(once you manage to burn out the flask and melt the metal. See
problems 2 & 3 above. That still remains.)

Delft clay is designed for a slightly different process, so it works
differently. It also doesn’t give quite the resolution of investment
casting, and can’t handle undercuts the way that investment casting
can. For the best resolution of the mold details (from the wax) you
need more force on the metal than you’d get by just pouring it in.
Thus the centrifuge or other casting method.

After re-reading this, I have a suggestion: find a copy of Tim
McCreight’s The Complete Metalsmith. Read the sections on casting.
Alternately, find a copy of his book Practical Casting. Either one
of them will explain the casting process in much more detail.


I know you want to do it all yourself, and I know it’s important to
you, but please believe me when I say you’re better off finding a job
shop to handle the casting. It’ll probably be cheaper in the long run
too, given all the kit you’ll have to buy to even make a stab at
doing it yourself.

Work on the wax model. That’s the part that’s really yours. The
casting is just a process. Done right, it’s pretty mechanical. The
final finishing will have more to say about what it looks like than
the casting should, if done right. So you can say that you did all
the parts that matter. (when you find a job caster, talk to him
about how to make the ring in such a way that it casts right. There
are tricks to that too.)

Best of luck, and congrats.
Brian


#3
I don't have access to a bell jar and vacuum pump etc. so am using
a (cheap) hand vacuum pump to pump the air our of an old airtight
jar - how much of a vacuum do I need to produce to get all of the
bubbles of of the plaster?? 

doesnt need to be perfect- degassing the water first will speed up
the process. Trying to degas mixed investment will take quite a bit
of effort with the small hand pumps sold for testing and setting
carbuettors but they will get there buut you plaster may set before
you have got rid of the bubbles. 29" of vacuum will do.

How hot do I have to cook the cast so I know all the wax is gone? 

There are 2 stages, the first is removing the wax and this can be
done in an oven at 80-100 deg C (190-212 deg F). The second stage is
the burn out and investment heating proper. This is done by ramping
up the heat to 500-550 deg C and keeping it that hot to ensure your
metal doesnt chill when casting.

I'm using a plumber's blowtorch to melt the gold (an old family
heirloom of a gold chain) - can I heat it too much? How do I know
the temperature is right? Can a plumber's blowtorch get hot
enough? 

Yes, the plumbers blowtorch will do, the nozzle may be a bit coarse
so use the smallest burner available that will have a flame that
covers your crucible but doesnt spill over too much nor heat too
small an area. Overheating the crucible makes it slightly porous and
too much heat on just a small area of the metal means that you wont
get it to flow and it can oxidise. Generally speaking you will not
overheat your gold in the time it takes to melt it properly. Keep the
metal together to reduce the surface area and sprinkle a little flux
on it. You can stir it (or prod it when it is partially melted to mix
it)with a carbon rod or even a dry twig- this will burn and produce a
localised reducing flame- to make sure that you metal is completely
molten and mixed and any dross comes to the surface. Scrape this to
one side before your cast. The metal will be hot enough when the
surface starts “swimming”- that is when it goes very bright metallic
looking and swirling under the force of the flame. You can prectise
with soem scrap silver, it will behave in the same way at about the
same temperature. Pour your practise cast into a prepared button and
sprue-no need to make another pattern- and when it has cooled quench
and look at the surface of the cast sprue and bottom of the button.
Is it free of wrinkles and filled properly? Does itm have a clean
surface or a frosted finish? If the former your mould is too cold, if
the latter, the mould too hot and the metal hasnt cooled fast enough
when cast and crystal growth has occurred.

I don't have access to a 'proper' centrifuge and am in the process
of making one using an old router. I've got some delft clay to make
our wedding rings which instructs just to pour the molten gold in
(it uses air holes so the gold moves down) why do we have to
centrifuge for lost wax casting? Can I not just pour it in? 

You can make your mould so that it has a large “button” above the
sprue so the weight of the molten metal forces itself into the
pattern and displaces the air. You generally wont need air risers but
they wont hurt. Centrifugal force is several time better than gravity
at forcing the molten metal into the mould and does so muck quicker
so you dont get choking by freezing on your sprues or tight corners.
It also uses less metal in the sprues and buttons as they can be much
finer. Consistency and quality are the reasons. There are other
methods used such as vacuum and squeeze casting but the equipment
costs considerably more.

Any mechanical or electrical casting machinery will have to be
properly balanced otherwise when you set it going it will throw
molten metal around which is beyond exciting to say the least.

Nick royall


#4

Hi Adam,

1.) I use a bombs-away method if I am using investment plaster, but
I often paint on a thin layer of plaster first. I don’t use a vacuum.

2.) The instructions are usually on the investment plaster container
you bought. Normal plasters (like plaster of paris), wont work.
Making you own investment plaster can be done, but the ingredients
are extremely hazardous, and as careful as I am with hazardous
materials, I wont do that.

3.) Usually not, you would probably need to build a furnace body to
accept a bilge type crucible to melt with that torch.

4.) You can use gravity instead of a centrifuge, it does work, but
the venting system you employ will be different.

There is definitely enough experience to help you with your project.

Regards Charles A.


#5

Adam,

You have set yourself up for failure with what you are thinking
about doing. Do not proceed without help.


#6

Adam,

Where are you located? If you’re near Fayetteville, NC, you’re
welcome to use my gear.

I don't have access to a bell jar and vacuum pump etc. so am using
a (cheap) hand vacuum pump to pump the air our of an old airtight
jar - how much of a vacuum do I need to produce to get all of the
bubbles of of the plaster?? 

As an alternative, you can do it more like “the old way” before
vacuum pumps were in use. Hand-paint your object with the investment,
making sure not to put any bubbles next to it. Put a couple of coats
on it. Then put your item in the flask and fill it up with
investment. Bubbles that don’t touch your piece don’t matter so much.

How hot do I have to cook the cast so I know all the wax is gone? 

The different brands of investment come with a burn-out timetable.

I'm using a plumber's blowtorch to melt the gold (an old family
heirloom of a gold chain) - can I heat it too much? How do I know
the temperature is right? Can a plumber's blowtorch get hot
enough? 

I haven’t cast gold, it’s out of my price range for the nonce. L With
bronze and silver, I like to see the metal flowing very freely, much
like mercury. No sluggishness to it, from top to bottom.

I don't have access to a 'proper' centrifuge and am in the process
of making one using an old router. I've got some delft clay to
make our wedding rings which instructs just to pour the molten gold
in (it uses air holes so the gold moves down) why do we have to
centrifuge for lost wax casting? Can I not just pour it in? 

When I do sand casting, I have to add risers - think sprues for the
air to get out instead of metal to get in.

It’s my belief that the centrifuge and the vacuum pump are - in large
part - substitutes for an involved enough riser system that would let
the air escape. Fewer risers means less clean-up on the piece, so
it’s a time saver and allows more of the piece to be decorated
(because risers aren’t connecting to it). Plus, of course, they help
the metal move faster/harder into nooks and crannies of the mold. If
you provide a way for the air to escape, and your ring doesn’t have
lots of tiny channels to fill up, you might not need a vacuum table
or centrifuge.


#7
Errr..I'll try to put this all gently, but focus on the wax ring.
Get that exactly the way you want it, then send it out for
casting. There are plenty of firms in the UK that specialize in job
casting. Trying to wing it yourself with the gear you've mentioned
is a recipe for disaster on a wedding ring. 

I really have to agree with Brian. If you want to get set up to do
this more than once you can buy a centrifugal force caster on Ebay
for less than $200 (search on “dental caster”)What you are describing
sounds dangerous. Although it COULD work, it would most likely take
weeks of trial and error to finally get good results.

I would be glad to cast it for you in my shop. But I am not very
convenient to you for travel. There must be someone in the UK who is
willing to let you participate. Most jewelers won’t, but some get a
kick out of it. I find it is good for business to let customers watch
when we recycle their gold.

Stephen Walker


Andover, NY


#8

Hi Adam, It’s a cool thing to want to make your girlfriends
engagement ring yourself. But casting is tricky and has many
variables that can negatively effect even an experienced casters
results. I’d say that with you having no casting experience, none of
the equipment and trying to use old gold rather than fresh, that
your getting a quality (even usable) casting is unlikely. If I were
you I would try to find a small custom jewelry shop who makes and
casts their own work in house and ask them if they will let you come
in and use their equipment and cast your model. They could guide you
through the process, make some suggestions and improve your odds of
success dramatically. They might expect a fee, but may be willing to
do it if you buy everyone lunch (or for a case of beer). It will be
an unusual request for sure, but that may work in your favor.


#9

My suggestion is that you try steam casting. There are some wonderful
tutorials on the internet. All you will need are a flowerpot and a
hot plate for burnout, some investment, and a casting device made out
of a large metal jar lid, attached to a section of broom handle or
dowling. The hollow of the jar lid is filled with wet newspaper, or
paper towels to provide the steam. Practice with some scrap silver to
get the feel of it. Although I have a complete casting
set-up–vacuum, programmable kiln, and centrifuge, I still do a bit
of steam casting when visiting a friend who has a place at the coast
and no casting equipment. It is a lot of fun,and we do get some
really fine castings. For melting our metal, we use a portable
propane torch. Works just fine.

Alma


#10

Hi Adam, Jo-Ann here in foggy SF…I just polished up two wedding/
engagement bands for a nice young man versed in the computer world.
He had made his rings in wax, also and wanted to do it all…But then,
he,too , decided to have his cast by a company here on the west
coast…Why? Two reasons–he knew that this was way beyond his
capability and tooling. Secondly, it was platinum metal-which is even
more complicated than gold. He did all the important work himself,
gave the complicated technical work to the pros and was still very
happy with the fact that he had made these–we were merely his hands
for a short time.

I have= cast over 40 years & believe me when I say ditto to Brian &
others:"Work on the wax model. That’s the part that’s really yours.
Thecasting is just a process. Done right, it’s pretty mechanical.
Thefinal finishing will have more to say about what it looks like
thanthe casting should, if done right. So you can say that you did
allthe parts that matter. (when you find a job caster, talk to
himabout how to make the ring in such a way that it casts right.
Thereare tricks to that too.) " It is so easy to f**ck up the metal
in a bad melt, you loose your wax and impression–that why it’s lost
wax casting…Bad casting means you start all over !! You have only
one shot at a time and the fact that you are recycling metal even
complicates that more.Plus no one has mentioned–you’ll need about
double the metal weight for the whole casting due to technical
reasons/ the button --the metal cools & pulls into itself etc.

You can do the cleanup afterwords, polish or texture away on the
final product and as Brian said–it is your work.

Good luck & Congrats…
Jo-Ann Maggiora Donivan, SF CA USA


#11

Hi Adam

Romance has blinded you, so it will not matter when your airtight
jar ceases to be airtight by exploding (imploding, really) and
blinds you that way.

Then your attempts to build an exploding centrifuge (routers spin at
24 to 30 thousand RPMs) will be so hard that you will be saved a
horrible death.

I DO get it though, Adam, but there is too much to learn here for
this to work within a reasonable time, and a lot of dangers that you
are totally unaware of - vacuums, molten metal, centrifugal forces,
acids, polishing motors etc.

Two realistic ways to go:

  1. Google for ‘steam casting’ and there are some YouTube vids too,
    but that only removes the vacuuming and centrifuging dangers.

  2. Better still, find a jeweler with a suitably equipped workshop
    who will allow you to ‘assist’ him as he casts, cleans and polishes
    your ring - safely.

Good luck in your future, but do try hard to have one.

Mark


#12

Adam, lost wax casting is a method that’s been used since ancient
times. You can do it without the fancy vacuum pumps and centrifuges
and all. The modern tools make it more precise, more repeatable,
faster, easer, and all that. But you can do it almost entirely with
equipment you literally can build yourself. Search the Orchid
Archives for “Steam casting” to find info on the methods.

In short, it works like this:

Your wax model is invested and sprued using a cluster of small
sprues to connect the main “normal” feeder sprues to the sprue base,
and the “funnel” that the sprue base forms in the investment is
scooped out with a spoon after the investment sets to form a shallow
melting crucible shape. The cluster of small sprues then show as a
group of small holes, rather than the usual one or two large ones.
The group of small sprues (usually somewhere around 14 guage wax wire
is used) should extend only a short distance below the bottom of the
"bowl" shape before combining into the larger simpler main feeder
sprues. Instead of a vacuum to de-air the investment, simply paint on
a thin layer of investment, blowing and brushing off adhering
bubbles, before then filling the flask up. Only a few bubbles from
the main pour will again find the wax, so you should be able to avoid
most bubbles on the model. They only matter if they contact the
model, which then gives you a little cast ball of metal on the
casting, which usually is not hard to clip or file off.

You can burn out the model using a simple home made muffle furnace
that uses your kitchen stove for heat. Gas is best, but an electric
stove works too. Only do this if you’ve got a good kitchen vent fan
to exhaust the wax burnout fumes to the outside, however. The “oven
muffle” is a simple red clay (terra cotta) flower pot, which you’ve
lined first with what used to be asbestos furnace tape, but is now a
similar looking insulating fire proof tape sort of material made of
other mineral fibers. It’s used as insulation in various types of
home heating furnaces, etc, and should be available in the hardware
store. Wet it so it’s pliable in order to line the pot with it. Then
line that layer with a double layer of aluminum foil, poke a small
hole through the liners to the hole in the bottom of the flower pot.
In use, the flask goes sprue hole down right on the stove burner,
with the flower pot over the top. The pot traps the heat sufficiently
that the flask will reach the needed temperatures to fully burn out
the wax (a low orange/red glow, or around 1350 F). This burnout will
take a number of hours. When the investment is again white colored in
the “crucible” area around the sprues, you’re ready to cast.

Casting is done with a simple device, which you’ve made before hand.
It’s a metal jar lid, larger in diameter than the top of the flask,
screwed to a handle, a bit of wood dowel or the like, so the inside
of the lid now faces out. You put a thick layer of newspaper in that
opening, and get it nice and wet.

Your metal is put into the shallow crucible area of the flask, and
melted, with a tiny bit of boric acid or borax flux, with your torch.
Because the sprue holes are those small diameter things, surface
tension of the metal will keep the metal from flowing down into the
holes until you force it down. You do that, when the metal is fully
melted, by quickly bringing that wet, paper lined jar lid down
through the torch flame to press down hard over the top of the
flask. It seals with the edge of your flask, and the heat from the
flask turns some of that water very quickly into steam, which
generates pressure. That steam pressure forces the metal past it’s
surface tension, and into the mold. Hold the jar lid/handle in place
for maybe 15 seconds or so, to make sure it’s had a chance to do
it’s thing. Then, once nothing is glowing any more, drop the flask
into a bucket (metal) of water, to quench it, break out the
investment, and reveal your casting.

This method is not foolproof, but it does work, and reduces the cost
of your casting setup to mostly the explaining you have to do to your
neighbors about that burning wax smell…

Because it’s not foolproof, you may wish to practice it first, with
a quick and simple sample wax model, perhaps using silver instead of
gold. Just so you can be sure it works, etc…

Email or ask on the list if you have questions.

Peter Rowe


#13

Hello Adam,

I am totally non-expert in casting but I must intervene in any case.
Your idea of using an old router as a centrifugal casting machine is
the closest thing to a death-wish i have seen in quite a while. A
router turns much faster than you can possibly need for casting. -
It turns so fast that whatever cockamamie ( with no disrespect)
improvisation you have attached to it will surely fly to pieces in
all directions at once and that would include any molten gold and
any other hot bits associated with it. You will surely be too busy
tending to your excruciating wounds and burns to do anything about
the fires set here and there in your surroundings by the red hot
splatters which have managed to miss being hurled deep into your
skin. Anything turning as fast as a router must be precisely,
symmetrically balanced to function without incurring instant self
destruction. This requires some advanced precision machining and
measuring tools.

As for the rest of your questions - there are plenty of folks on
this forum much better equipped than myself to answer them.

Please use your head as well as your loving heart. The scars
resulting may reduce your chances of getting a “yes” from your
intended bride.

Marty in Victoria where things just never go wrong.


#14
My suggestion is that you try steam casting. 

Steam casting scares the cr*p out of me, and I used to use a sling
caster :open_mouth: CIA


#15

Hi Adam,

You have had the best advice from the pros here on this forum, and
you would be advised to take their word for it. I do understand your
wish to make for your hearts treasure this engagement ring, but your
obsession to do it via casting is hard for me to understand.

you need to step back a bit and ask the question, what other ways of
making this are there? that I CAN do without killing myself? You need
to consider woven or twisted strands of wire, to a hammered shape
from the ingot cast from the gold you have to hand. There will be so
much more of you in the ring if its wrought.

Every hammer blow is part of you going into the metal. Now I
appreciate cast work for what it is, but it doesnt interest me,
never did, all my work is wrought, hammer made. I made my wifes
engagement ring and wedding ring from 18ct gold,using 6 strands of
wire, twisted tight, then hammered into a D shape in a steel
depression.

this was a length some 12 in long from which I made the rings, gold
soldering up the join each ring was 2 rounds of the D section to
symbolise our partnership…

The.4 carat diamond was set in a simple claw setting in white gold
soldered on where the ring join was made. they have stood the test of
time some 40 yrs later. hope this gives you something to think about,
thats outside your current mind set.

There is a difference between cast and wrought work. I know which
talks to me nicer!!

Ted
In Dorset
UK


#16

Adam,

You don’t NEED all that much equipment. Nice to have but not
essential for your project. I’ve been steam casting for over thirty
years. Have also used centrifugal and vacuum, but stay with steam
because if suits my requirements just fine. I could go on in great
detail to explain the procedure, but thanks to the marvels of modern
thechnology we havegoogle and youtube. Just google “jewelry steam
cleaning” and check out the results.

Jerry in Kodiak


#17

Thankyou all so much for your time and advice! I can’t tell you how
appreciated it is!!

I’m so glad to have been told about steam casting!! My wax casting
is fairly intricate as it has a kind of ‘braid’ in it. I’m assuming
if I’m painting the model I can just make sure I get the investment
into the holes and it will be ok?

Does anyone know where to buy good investment in the UK? I don’t
know what to google as I can only find industrial sized bags!

I appreciate the advice about going to a professional caster but
where I lives makes this more than impractical and I can’t really
seem to find any in the UK. I appreciate that professional things
should be left to the professionals but am indeed maybe a bit
blinded and niave by my intentions.

Massive thanks to those who have said that I can use their kit!!

I think I’m going to try and make some of my ‘failed’ wax models as
they are faily representative of the final design and hopefully will
give me a good idea of the result. I’ll see how they come out and
make a bit better info rmed decision then!

Wish me luck

I’m sure I’ll be back when I actually start the process full again
of questions

Can’t thank you guys enough

THE ROUTER AS A CENTRIFUGE IDEA HAS BEEN ABANDONED!! Lol!!
Think I scared a few with that one!! God knows what I was thinking!
Thanks to all for saving me!!


#18

As someone who has been self taught in casting over the last 2 years
I agree that Adam should make the wax model and hand it off…or
practice steam casting with silver until he is comfortable with that
method and then try the gold final piece.

It can be done with minimal tools Adam, but it took me two years of
practice to know how to get all the little things just right. Just
like my other hobby fields, buy books, they are your best
friend.

Rick Powell


#19
Does anyone know where to buy good investment in the UK? I don't
know what to google as I can only find industrial sized bags! 

You could try with dental laboratories. Not only do they do castings
(and they may love to help you: anything other than teeth is an
exciting distraction to them), but they have small packs of
investment. More expensive in relative terms, but if you just need
300 grams… makes me think of that bonmot from a bachelor: Asked why
he doesn’t want to marry, he replies: “Why buy a cow, when I can have
a glass of milk at every corner?”

Oops…


#20
 Does anyone know where to buy good investment in the UK? I don't
 know what to google as I can only find industrial sized bags!
You could try with dental laboratories. Not only do they do
castings (and they may love to help you 

A word of caution though you’ve got to tell them what you are going
to use the plaster for, otherwise you may just end up with hydrocal
or stone. CIA