2 Hours Casting

Ok everybody… Listen up cause I have a good one for you all…
It seems as though a freind of mine has stumbled upon someone who i
might have to consider some sort of God… Firts let me tell everyone
that I have been a jeweler for eight yearsnow and I have been doing
design and casting work for about four of those eight years. Now I
know for a fact( or now what I thought was fact) that in any kind of
lost wax casting method used weather it be centifical or vacum
casting, you would normaly burn out for a good healthy 8 hours
minimum, to get the best results. Well here is why this guy must be
some kind of God… My freind says he can give a wax model to this guy
at 10 oclock Saturday moring and he will have it back in a perfect
casting by 12 oclock noon the same day… If anyone with any
knowledge of casting knows how to pour investment and burn out then
pour within a 2 hour time period… please let me know. I don’t know
about anybody else but my investment takes a minimum of an hour
before I would even think about putting it the oven… Is there
another way to burn out and cast other than Vacum and Centrifical???
And I know a little about steaming the wax out but you can’t steam
out carving wax… Anyone… please comment I would love to know
weather this person really is a God…

I doubt it highly…
Thank you Marc

Hello Marc,

your friend is not kidding you!

There are so called Speed-Investments in the market, wich can be
used in the discribed way!

We produce an Investment called Invest C/P, that allows a process
time (from the start of mixing to the end of the casting process) of
90 minutes or less!

The benefits of these Investments are their short process times and
the fact, that they can be used with nearly any alloy except

The big difference to gypsum bound investments is their stability.
These Investments are much harder than the gypsum ones. When quenched
after casting they will not fall apart as known but you will have to
remove the Investment by hammer or sandblaster.

This stability is needed to withstand the extreme short processing
time. For example: the Investment sets within 15 minutes and can be
put directly into the preheated furnace at 950 celsius, heated up for
45 minutes and then can be casted!

If you would like some further Informations, please do not hesitate
to contact me at any time!

best regards

Rouven Cser
Ti-Research GbR
e-mail: info@ti-research.com


I’ve been lost wax casting for some 35 years, and have picked up all
kinds of tricks, tips and folklore along the way. Yes, you can do a
casting from investment to finished casting in about 2 hours, but
not many would recommend it. I have done it myself a few times when
I was in a big hurry. It works best with smaller waxes and small
flasks. The investment will set up in 15 min., hard enough to pop
off the rubber base. Into the oven with it, and start bringing the
temperature up quickly. Because of the smaller size, it seems to be
less prone to thermal shock and cracking than larger flasks. The
moistness of the investment will help steam out the wax better than
a dry flask, according to experts I’ve spoken to. So you run the
oven up to 1350 degrees, and when the inside of the sprue button is
clean and white, showing no wax residue, turn off the oven, open the
door to bring the heat down faster, and cast when there is no red
glow on the interior of the flask The casting experts out there as
well as the investment manufacturers will go crazy with the short
investment set up and burn out times, but it can be done.

I’ve also had old-time jewelers claim you get the best results
casting flasks at room temperature, and even some Mexican jewelers
I’ve heard of who insist you have to stir your molten metal with a
chicken bone. Everybody’s got their own shortcuts, weird beliefs, or
voodoo they use to get their castings to come out right. Who’s to
say what works best? I think metalsmiths need the best, up to date
we can get, and then should go out and experiment like
crazy. Push the limit, and see what happens. How else will you know
what you can accomplish and how far you can push the materials?

Good luck!
Jay Whaley UCSD Craft Center

Marc, I’ve been doing it for years. No big secret really. It just
takes special investment and a really hot oven.

Here’s the process I use here.



I may be wrong but these are my thoughts.

It depends a lot on how many flasks you have in the burnout oven and
how well the oven breaths.

In order to properly burn out wax, the flask must remain at burn out
temperature long enough for the carbon to combine with oxygen to
form a gas and leave the flask. The more wax you are trying to burn
out the longer the flasks need to be maintained at burn out
temperature. The less oxygen the oven receives the longer it will
take to burn out the wax.

It is stated in the book “Design and Creation of Jewelry” by Robert
Von Neumann: “Dental casting literature describes a short burnout
schedule of 1 to 2 hours. The flasks for most dental castings are
small and contain little moisture or wax.”

I imagine you can compare it to burning a small stick as compared to
a big log in a burn out oven. The bigger the stick the longer it
will take to burn it out. With out oxygen there will be no burn out.
Same with wax.

I know jewelers who will take the flask up to burn out temp and back
down and cast. The flasks are small and contain little injection
wax. Carving wax will take a longer time to burn out.

By the way if you vacuum cast check the two papers on orchids bench
tips. They describe a very simple way to prevent fire scale when
vacuum casting. The process works. No firescale.

Lee Epperson

Investment normaly sets up in less than 15 minutes. A small flask(2")
can be dried in the oven in 30 minutes. A quick ramp up to 1400 and a
short cool down will allow for a casting to be done in 2 hours. Not
something to be done with a larger flask, not something that I like
to do on a regular besis, but something that I have done often enough
to know is very possible. The greatest danger seems to be in boiling
water out of the flask too quickly as this causes cracking of the
investment. Improper casting temperature will also impact the

No, he’s not a god. Lucky maybe.

Ask your friend: I bet he’s doing small things like single rings and
pendants, yes?

With the sorts of tiny flasks you use for those, you don’t need
nearly as much soak time to get the insides up to temp as a big
4-5-6 by 6 inch flask holding a whole pinetree of stuff would.

With little flasks, you can get away with that sort of abuse. In
emergencies, I’ve done 4x5 flasks in a 4 hour burn (+1 for setup)
and had them come out fine. I used to know someone who would just
put a recently set-up flask right straight into a kiln already at
1300F, wait about an hour, and cast it…at least if it was small.
Of course, those sorts of stunts are riding on the ragged edge of
disaster. Not something you’d want to do if you had a choice.
Investments have gotten much better in the past few years, and now
you have a much better chance of getting away with doing a burnout
like that, but understand that you’re depending on the investment to
be good enough to make up for the fact that you’re being a bonehead.

If you’ve got the time to do a proper burnout, do it. Just because
you can do a thing, it does not follow that you should do that



Hi Marc;

I’ve done this kind of thing, in desperate situations, but it’s a
gamble. The investment is pretty solid after a half hour, and I’ve
done that then put it in a kiln and ran it straight up to 1350
Farhenheit, then turn off the kiln, open the door, close it after it
drops down to 900, wait till it comes back up to 1000 and evens
everything out, then cast. I’ve only done this a couple times but
never had one blow up on me. I don’t recommend this as a typical
casting method. I usually use small flasks, and do fine with a 5
hour burnout cycle, but if I’m using larger flasks, over 2.5" X 3" I
add another hour at the lower end where most of the strain takes
place. Your guy isn’t a god, more likely just a bit of a hot dog.

David L. Huffman

My freind says he can give a wax model to this guy at 10 oclock
Saturday moring and he will have it back in a perfect casting by 12
oclock noon the same day.... If anyone with any knowledge of
casting knows how to pour investment and burn out then pour within
a 2 hour time period.. please let me know. 

Go to the Precious Metals West web site, at


On the list on the left of the home page, click the new products
link. Scroll down to the second product, their “supersonic”

2 hours may be a stretch, but they say they can do it in 3 hours
with that investment, and I’ll bet that with a small flask, and
perhaps pushing the times a bit, one could shorten it from there, too.
Remember that some of the new investments will tolerate both a
shorter setup time after pouring, and when set, can be put directly
into a 1500 degree kiln, greatly shortening the the burnout.

Heck, with small dental size flasks, and not a great success rate,
I’ve managed that on occasion with plain old satin cast investment,
using hotter water than specified in order to shorten setup time. Not
all flasks survive this, but I’ve managed it once or twice just to
see if it could work. About half the time it did, and I might have
been able to fine tune it to improve the results. I’d use warmer
water, and a fairly thick mix for strength, put in the kiln at a
half hour, with the kiln at 1500, but turn it down when the flask
went in. The kiln would have dropped to about 1350 to 1400 about the
time the flask got up to temp, and it would have about an hour to
burn out before I’d cast. These were very small flasks, barely big
enough for one ring, using a furnace tape liner to help with
expansion, and cast in a small dental centrifuge. The surfaces I got
were often rather on the rough side, but as I said, this was plain
satin cast investment, nothing special.

Bottom line, never say “never”.


I call this guy Dad… he’s in Florida. Not really into casting much
though. But I’ve had same day castings before.

It’s always heavy stuff because you’ll be doing a lot of filling,
but if you need to cast a contour band for example and set a few
small diamonds into it, it can be done. You just accelerate the burn
out and dont pay attention to the black in the investment hole. I
did see him running the kiln way up to 1800 degrees as sson as it
hit it, we lowered the temp, waited for 12-1300 to come around and
vacuum casted it. Also- I’ve pulled the rubber bases off of flasks
after about 30 minutes. Having said all of this, I still think it
takes a little longer than 2 hours. (At least this way…we’re just
imaptient sometimes…)

Stanley Bright
A&M Jewelers
Baltimore, MD

1 Like

its true ive been doing it for years and if im in a real rush i can
doit in 1 1/2 hours - goo

I have seen a demo of dental type investments go from wax to metal
in a couple of hours. They are typically used for platinum but can
be cast in gold or silver as well. The ones I have seen are not the
highest surface finish when burned out that fast but they are
useable with a fair amount of finish work. I use some of the stuff
but burn it out longer to improve the surface finish.

James Binnion
James Binnion Metal Arts


There really isn’t any mystery to this…the secret lies in the
size of the flask and the ability of the casting unit to operate
with said flask. I regularly do castings in a span of three hours,
but could also do it in two hours if need be. In my case I am using
a hundred year old vertical dental casting machine and 1 1/4 " x 2"
flasks. In these dimensions investment sets up much faster and the
burnout is a piece of cake. I used to have a Ney casting unit, but
it is not nearly as efficient with small flasks…otherwise it is
a very slick machine. Obviously, within these dimensions, these
flasks are only good for small objects, but, since we all mostly
cast rings, it is ideal for that purpose. Ron MIlls, Mills Gem Co.
Los Osos, Ca.

I forgot to mention there are several problems with these fast

One is they are very hard they must be broken off the work. If you
are not careful you will damage the work.

They also tend to leave small amounts of investment firmly attached
to the work that must be dissolved off with a strong acid or lye.
Surface finish is rarely as good as you can get with gypsum bonded

The only reasons for using them are you need the high temperature
characteristics for platinum or other high temp metals or you have
to have it cast today. Otherwise there are too many hassles with it.

James Binnion
James Binnion Metal Arts


Hello! One store I worked for in Illinois had to do a 45 minute
burnout during Christmas -on Christmas Eve (hysterical, wild-eyed
last-minute husband). But that didn’t include letting the investment
harden, the wax was steamed out first, and we started the project at
10 that morning, and the guy I worked for delivered it to the
husband at about 8 that night, after we finished the ring and took
apart another piece to use the stones. We were giddy about 12 hours.
Can’t imagine 2. Either this guy’s friend is putting him on, or he’s
getting electroformed and plated wax from this “god.”

just my input,

He’s right I’ve seen goo do it in his work shop less then 2 hours,
just to show me how, while I was visiting him in Dublin OH.


Most casting protocols are cookbook-like and don't explain
what is going on. The objective of burnout is simply to get rid of
the wax in the pores of the investment to make it porous and
strengthen the mold so that it is more ceramic like than simply
hard plaster. As you pointed out, when the pouring cup is chalky
white instead of grey, all of the wax is gone. We can get to about
1350 F as fast as possible if the oven is already at that
temperature instead of starting out at room temperature or 300 F as
often suggested. The free water in the pores of the investment will
keep the mold temperature from rising above 212 F (the boiling
point) until all of the water has turned to steam. Then the
temperature rises rapidly to almost the oven temperature to
complete the burnout. I have placed a thermocouple in the center of
a 2 x 2-1/2 inch flask and showed that the core temperature stayed
at 212 F for about 20 minutes and then the temperature rose to
almost 1350 F in about another 40 minutes. 

I read the post from Fred Sias with a lot of interest and I agree
completely with the main theme of his teaching. I would like to
respectfully add a few little details and some context for people who
might be casting larger flasks. Fred and I had the same teacher if he
is talking about the late Dr. Carl Schwartz. It is true that keeping
the outer surface of the investment from drying before the interior
will help prevent cracks when the investment is heated rapidly.
However, you need to keep in mind that as the diameter of the flask
is increased the speed that it can be heated slows down
exponentially. In part this is because the investment is a good
insulator and like all insulators the thicker it is the better it

The Santa Fe Symposium has published many papers on investment and
burnout over the last 20 years starting with one by Schwartz and
followed by Ott, Schneller, Ingo, McKeer, McClosky Carter, Horton,
Loewen and me (These come to mind, I hope I didn’t leave anyone out).
The heating rate of various diameter flasks has been measured and the
results published in SFS '88 and '89 and they show that the first
inch of investment thickness next to the flask wall can be heated
fairly quickly when there is a large temperature differential between
the oven air and the flask as Fred points out. This is proven daily
by the hundreds who cast small 2-inch diameter flasks. By the time
the flask diameter reaches 4 inches (100mm) it takes a minimum of 3
hours to get the center of the flask dry. If you hope to cast into an
investment mold that is not spalled or cracked plan on about 5 hours.
On first heating, the watered investment is quite conductive, but as
the water is driven off it becomes isolative. Once the first inch of
investment is dry it insulates that which is further inside.
Interestingly, a four inch flask reaches temperature equilibrium (the
same temperature from the flask wall to the center) in about the same
number of hours wither it is heated as fast as possible, or with a
reasonably slow ramp rate. The bottom line is, it you cast larger
diameter flasks, don’t try to burnout in two hours, you need between
12 and 16 depending on the equipment and the load in it.

Set investment when mixed with water at a ratio of 40:100 is about
50% water by volume because the investment powder has a higher
density than and the binder already contains about 6% water. When the
water is driven off the space it took is empty and the investment is
quite permeable or porous. This is also why it becomes such a good

The reason the wax must be completely removed is the residues of wax
is carbon and if carbon is present in the investment when the metal
is cast a chemical reaction rapidly decomposes the gypsum used to
bond the investment. The result of the decomposition is the release
of gases that are detrimental to casting and the general health of
your metal.

When investment first sets it is quite fragile. Slowly the dissolved
plaster precipitates and gypsum crystals grow. Over a two hour span
what is called green strength increases until it is safe to handle
the flasks to remove the sprue base and start the burnout cycle. The
green strength will go up to 350-400psi compressive strength. During
the burnout most of the strength is lost and the typical invested
mold is only about 20% as strong when it is cast as it was when the
burnout started. The biggest factor causing this loss of strength is
the loss of the water. Then depending on how high you take your peak
burnout temperature, some of the binder is also lost starting at
about 1200 F. Still if everything is done correctly, the investment
is plenty strong to get good smooth as-cast surfaces and reproduction
of detail. Investment manufactures could make the investment stronger
but the tradeoff is, stronger investment is more difficult to remove.

Eddie Bell

Eddie, It is about time someone got straight to the point in this
casting discussion !

Your dissertation is that and I am grateful for your in depth
analysis of the subtleties of casting and investing. I have on
numerous occaisions attempted to promote the use of small flasks for
single wax castings inasmuch as it is as much more expeditious way
of production for studio type operations. My old vertical casting
machine has been faithfully turning out quality castings using
1 1/4" x 2" flasks for several decades and…they typically take
only 2 to 3 hours from start to finish. Unfortunately, most of the
casting machines that are available to the small time operator do not
meet that need. Even the Neycraft is not particularly well suited for
use with small flasks. Don’t you think it is about time that we
produced a casting unit of this type? Dental labs have been using
this technology for a hundred years even though they are now using
equipment that is aimed more at high temperature , high production
applications. If I were burgled of my equipment, the first thing I
would mourn would be the loss of my ancient dental casting machine.

Ron Mills at Mills Gem Co. Los Osos, Ca.

My thanks to Eddie Bell for clarifying the requirements for large
flask burnout. My experience is mostly with small flasks. I see I had
some incorrect ideas regarding the change in investment strength
between the start and end of burnout.

I wish I had all of the Santa Fe Symposium papers you mentioned but
the university interlibrary loan folks got unhappy when I kept
ordering reprints of different articles. I couldn’t afford to buy all
19 volumes.

I would like to know if disappearance of the grey and a change to a
"chalky appearence" of the pouring cup is a “sufficient” indication
of adequate burnout even in the large flasks. Otherwise is there any
clear indication of sufficient burnout other than inserting a
thermocouple or allowing more than enough time?


Dear Fred,

I would like to know if disappearance of the grey and a change to
a "chalky appearence" of the pouring cup is a "sufficient"
indication of adequate burnout even in the large flasks. Otherwise
is there any clear indication of sufficient burnout other than
inserting a thermocouple or allowing more than enough time? 

The white color of the investment in the area of the flask where
metal will contact is a practical measure because we can look at
every flask before casting. It is not a guarantee that the cavity is
completely carbon free, but for the most part I look for other
problems when diagnosing gas porosity if the flask was white before

Why do we care about a carbon free burnout?

Chemically carbon acts as a reducing agent in investment. When there
is carbon present in the flask as a result of incomplete burnout it
drives the reaction temperature of the gypsum used as a binder in
the investment down below the casting temperature of most of the
alloys we cast. Carbon free investment starts thermal reaction at
about 1100C (2012F), which is high enough for our needs but if
residual carbon is present the reaction temperature is about 700C or
1300F. As the cast metal cools it gives up energy, heating the
investment until the reaction temperature is reached and sulfur
dioxide gas is liberated and absorbed by the hot metal. It is easy
for metal that is between 1600 and 2000F to raise the investment
from say 1000F to 1300F or higher.

Gold is pretty inert but all the alloying metals react with SO2 and
cause porosity and unwanted metallic/sulfur compounds and oxides.
Silver casting is much more sensitive than gold casting because the
silver contains about twice the energy per gram (it is better able
to heat the investment wall) and the silver likes very much to
combine with sulfur. A rotten egg smell on the casting as it comes
out of being quenched is an indicator that SO2 is present. Another
in-shop indicator is residual slag in the crucible after melting
metal that has been exposed to SO2. However, melting previously cast
items or sprues that are not completely clean of investment will
produce slag and contaminate the metal too. Pickle has been found to
be another source of contamination. It gets into the cracks and
pores on the sprue and will only rinse out in an ultrasonic tank
with clear water. If you see little green or blue spots on the metal
after it has been pickled and dried, it is a sign that the pickle,
which is a sulfur compound, was not completely rinsed away.

Some casters use forming gas (a mixture of 93% nitrogen and 7%
hydrogen) and that can be a problem too. According to Dieter Ott,
Hydrogen is another element that will act as a reducing agent in
investment causing the same reaction that carbon does, so if you use
forming gas and have problems that look like gas porosity and
contamination you might want to switch to argon.