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Casting frustrations

Jagman/Skipmeister: I just polished up some of the de-ox pieces
I did and NOOOOO----still got pits!!! What burnout schedule
do you use and what investment do you use? I’m wondering if
larger pits can be caused by investment steaming out into the
flask. Will that cause pits? It seems no matter WHAT I do I get
some pits. I’m using that AG100 investment from Rio. I heat soak
my flask for an hour at 800 F before casting, my pieces are
usually fairly chunky. The pits are just below the surface
usually. I’ve been doing this for 4 years now and cast
infrequently and really frustrated. I’m using propane/oxy with a
bud tip and if I’m getting pits with the de-ox stuff I guess
oxygen isn’t my problem. Is it really possible to cast without
porosity in a home studio? I use a kiln controller to set the
burnout schedule. This last cast was with injection wax and used
wax-web too. I even pray to the silver gods and they just laugh
at me…Dave

Kickass Websites for the Corporate World
Crystalguy Jewelry
Recumbent Cyclist’s Advocacy Group

Dave, Call me at 401-461-7803 to solve your casting problems ,
i need to ask quetions about your materials, equipment, methods
pieces etc.

Dan Grandi
this is on th eastcoast time … i am here late as well

Aloha Dave, Sounds like you are casting at too low of a
temperature (800 Degrees). You should be casting silver at 1000
to 1200 (depending on the item mass). Vacuum should be at 1200
degrees. The time it takes to position the flask in the casting
machine and then sucking ambient temperature air thru the flask,
will lower the internal temp, by a couple of hundred degrees.
Also, it is better to premelt your metal prior to pulling your
flask out of the oven (if you are not already doing so), situate
your flask, and then remelt, your already preheated metal. May
the silver gods smile upon you. I hope this was of help.

Best Regards and Happy Holidays,
Christian Grunewald
Precision Modelmaking

This suggests that what’s happening is that your flask is too
cool. metal hits the flask wall and freezes, and then shrinkage
effects as the rest of the metal solidifies more slowly, deplete
the subsurface area, creating shrinkage porosity below the

Increase your sprue size, so the sprue stays liquid longer. It
MUST be as heavy, or heavier, than the heaviest part of your
model, and it must be centrally oriented to the axis of the
flask. Then increase your heat soak temp to about 900,
especially if your using a vacuum cast. And THEN, when you
remove your flasks from the kiln, wait a couple minutes, letting
them gently air cool, sprue hole down on an insulating pad,
before you proceed with casting. What this does is create a
temperature differential between the outer portion of the flask
and the inner. The outer area of the flask will have cooled a
hundred degrees or so in that minute, but the core, with the
sprue, will not, too much. so your sprue and the portions of the
model at the center will stay liquid longer, allowing a better
sequential solidification to occur, and preventing that
starvation just under the surface that’s giving you that

Peter Rowe

Dave: It is indeed possible to cast sucesfully in a small shop. I
don’t go to all the trouble to “burn out” my crucibles, simply
cover them tightly with aluminum foil when I’m done. Use simple
boric acid powder (not a lot) for flux and usually have no
trouble at all. If however, you should still have a few
pits(especially the cloud of smaller pits on large flat surfaces)
it’s a small(3/4")wheel which mounts on your flex-shaft and
burnishes them away! After treating the spots, simply emery
smooth & polish. Works great. If you’re interested, I’ll send
you the adress of the supplier.

Steve Klepinger

Dave, Call me at 401-461-7803 to solve your casting problems ,
i need to ask quetions about your materials, equipment, methods
pieces etc.

Don: I’ll give you a call monday or tuesday nite, will give me
time to get all my info together also. Peter Rowe had a good
reply and maybe he’s right about the flask being too cool, though
it bugs me that on my Neycraft Spincaster when you melt the metal
you’re also sending a flame into the flask and wonder what effect
that has on flask temp…hmmmmmm…Dave

Kickass Websites for the Corporate World
Crystalguy Jewelry
Recumbent Cyclist’s Advocacy Group

Hi Dave, If it isn’t possible to cast in a home studio, I have
been deluding myself and the numerous client dentists that I’ve
serviced over the years!:o)

Dave, there could be a number of things wrong.

  1. Your wax may have pits in it (I doubt it).

  2. Your investment might not be set yet or it could be out of
    date. (very possible)

  3. Your burnout is not getting hot enough to completely
    eliminate the wax and carbon residue.(At 800 deg.F that is a
    distinct possibility, so I would run it up to 1000 or 1100 deg F
    and then drop it back to 900 Deg F)

  4. You are very likely getting the metal TOO HOT! Oxy-propane
    in a rosebud tipped torch can be damn hot. Melt the metal
    slowly, take your time. Flux lightly and bring it up to melting
    temp. Slowly bring it up to casting temp. Watch for the metal
    to start rolling gently and also watch for the subtle color
    change from the orange/red to the yellow/white.(I don’t describe
    it very well but I know it when I see it!:o)

  5. You do not have the sprues large enough or possibly in
    enough numbers or possibly both. This is a very good

I cast with a Kerr centrifuge. I use Jelenko complete
investment which I bench set 'til it get cool to the touch. I
then put it in my Ney computer controlled COLD burnout furnace.
I raise the temp at 32 deg F per minute until it gets to 1200
deg F. This is generally too hot for silver(filigree is fine at
this temp)but just right for gold. When I’m ready to cast, I
put my cold crucible in the cradle and add the metal. I NOW PUT
. I start the melt with
the casting ring in place. When it gets hot enough to cast, I
let her fly. I let the broken arm slow to a stop then I may
wait longer before I quench. I pick off as much of the
investment as is possible and put the casting in the ultra-sonic
in a covered plastic beaker with either ‘Strip-It’ or 'No San’
investment remover. This acid will strip porcelain so it is
pretty strong, but it is not hydro-floric acid.

Were I to guess, it would be a combination of spruing, melting,
burnout temp and possibly incomplete setup of the investment.

Dave, I think that you have my phone number so you can give me a
call, or you can e-mail me.


Skip Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor

Steve, what is the 3/4 wheel your using to burnish porosity?
Thanks, Slone

Hi Dave, Your casting problem sounds like inadequate spruing. The
sprue must be slightly larger than the section you are spruing
to.You must also feed each isolated thick spot with it’s own
sprue. Remember that molten metal is in an expanded state and
will shrink and pull itself apart without adequate feed to each
of these “Hot Sots”. Also watch your metal and flask temps. If
things aren’t filling raise the flask temp NOT the metal temp.

Hi Dave, The old ‘flame in the hole’, as we techs call it, serves
to keep the mold warm and also any residual combustable gas is
’eaten’. Don’t worry.


Skip Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor

It may be as simple as … Do you use a vacuum oump to take the
air out of your investment? you did not say Good luck Ron

though it bugs me that on my Neycraft Spincaster when you melt
the metal you're also sending a flame into the flask and wonder
what effect that has on flask temp...hmmmmmm...... 

It may tend to keep the sprue area from cooling, or even heat it
a bit on the outside. Won’t do much beyond the exterior cone.
All in all, shouldn’t hurt, and probably is a beneficial effect.
But if it bothers you, try a sheet of thin stainless steel,
between the flask and the crucible. You’ll need to leave them
slightly seperated, and when the metal is ready to cast, slip
out that sheet, push the crucible to the flask, and let-er-rip…


Dave: You may not be shooting enough metal into the casting
cavity. You need to weigh your wax model with the sprue attached
to the model, but before actually sprued into the rubber flask
bottom. Then multiply the weight by the appropriate factor for
whatever metal that you are using and then add a little extra.
For example:

Sterling silver is 10 X 1 + 10%; 14k gold is 14 X 1 + 10% So if
the sprued model was 2 dwt, the amount of casting sterling would
be 2dwt x 10 + (10% X (2dwt X 10) = (20 dwt + 2 dwt) = 22 dwt

The additive factor at the end of the formula (the 10% part)
should be increased if you are casting a really large piece, or
several pieces that will be sprued together. This is because you
want the force of the hot molten metal to really pack into all
the void spaces of the investment before the metal cools. If I’m
casting something that calls for 40 dwt or above, I may increase
the additive part of the formula to 20% or 30%.

You also don’t want to keep the torch on the molten metal too
much longer after is has achieved a good liquid state in the

Good luck

Virginia Lyons

Hi, All, first let me say I’m happy to have the opportunity to
throw out a question to the group. I’ve been sort of following
the discussion of casting woes, and I have one of my own, since I
cast for the rest of the shop, for me it becomes a larger issue.
That issue is bubbles…you know those annoying little ones
that cling to the outside of the great ring you just cast and
some jeweler took two days to carve. So far I haven’t had any
really bad bubble incidents, but I’d like to nip this in the bud.
Now one or two tiny bubbles I could live with as long as there
not in a critical spot on the casting. But, lately I’ve got 10 to
20 little bubbles per casting. I use a debubbler fluid from Rio,
and the vacuum table I use can vibrate [manually] but the
investment instructions say it’s not necessary, so I don’t shake
the table much, and haven’t for quite awhile now. So I guess the
question is, why now? Oh ya, and some of the castings lately have
been with diamonds set in the wax, so I been adding 2% boric acid
to the investment, and on those castings the investment does
change consistency somewhat, but the rest of the process seems
to go fine. And I can’t really single out those castings as
having more or less bubbles than the regular ones. Is there a way
to be totally bubble free? I and the rest of the jewelers
currently chained to their benches till after the Holiday crush.
Would like your comments and suggestions, thank you. Best Regards
Brenda PS Thank You Dancing Horse for the welcome.

Interesting you use “flame in the hole”; the miners in Penna.,
WVa, Ky, etc., used to use “fire in the hole” to indicate to
others to lay low as a dynamite charge had been set and an
explosion was emminent. Sharon Holt (my dad was a coal miner
back in the late 30’s early 40’s in WV.)

Hello Brenda,
For many years, I designed , built and sold equipment for lost
wax casting (as well as other types of machinery) and their
related supplies. What i could tell you about bubbles beginning
to occur more frequently is the following.

  1. make sure that your bell jar flange is absolutely clean and
    if you have the capability, check that it is absolutely flat.

  2. check all seals… use plenty of water on the seals… this

  3. depending on your vacuum pump, do a complete service on the
    pump… remove any accumulated sludge, change the oil and filters.

  4. vacuum gauges also go faulty and may be lying , so if after a
    full cleaning, your pump should be able to " boil " water in the
    bell jar at 72o vigorously.

  5. test a different or new batch of investment.

  6. check your water temp thermometer for accuracy… If this does
    not cure the problem, then increase your water temperature by 10
    degrees and your water /investment will boil easier and set up
    about 20-30 seconds faster… so adjust your timing accordingly.
    We have used water temperatures as high as 120 degrees in
    emergency production situations with NO ILL effects… just
    realize that the invest ment will set up about 1- 1 1/2 minute
    sooner than expected. Most investing problems can be traced back
    to either the operator not following the investment
    manufacturers specs, malfunctioning machinery and periodically a
    bad batch of investment.

Merry Christmas and Happy New Year…
Dan Grandi

Hi Brenda, Vibrate the table by all means. Do you have a guage
on the table? It is always possible there is a small leak.
Good luck. Tom Arnold

Have been sitting back and reading all the casting info for a
few days. I may have missed some as I have been busy but in the
past I have had some problems with pits, more like porosity. I
mean this thing hung around for some time… I tried every thing
change investment handling, more water, less water… Cure the
flask underwater, You can do this just put it in a bucket full of
water. Changed burn out and even sat and watched burn out
thinking I got a temp spike some how. Well I was going nuts…
So I found out and I think it was on line here at (Orchid) a
month or so ago or it may have been in the archives but it
turned out to be the mixing of wax… injector wax for the wax
pattern, then sprue wax for the sprue, but I was using a
different kind of sprue wax for altering or repairing a wax
pattern and for attaching the sprue to the sprue base. The wax I
was using melted at a different temp and was keeping the already
melted wax, (injector or sprue wax) inside the design and boiling
so it was messing up the surface and even going deeper in to the
investment causing the problem… This all stared when a friend
brought over so injector wax for me to try with no information
about the wax… I was out and tried it it was ok … One thing
to remember is if you are having a problem with casting go back
to the basics, then check everything you do that is
different…Casting is not hard if you have the basics down…
In 800BC the Atruckins, I think or the Egyptians us cow Dung as
investment and a good old fire to do burn out…

Oh ya!! A burnisher is OK but using it to cover up pits is
that not just covering up a mistake??? That is like using solider
for a tip on a gold ring (Not using the gold half sphere)… If
you get a Pit drill it then fit a pin ( the same type of metal
you are drilling) and solider it in and refinish. If you get
porosity you must figure out what you are doing wrong… I have
used a burnisher on a job or several jobs but only after the
customer was made aware of the problem… See the metal that you
push over the porosity or pits will ware off in most cases as
pits and porosity are commonly found in wear areas of rings
unless something real wrong went wrong. In this case you need
more than a burnisher…The guy that taught me casting first of
all he would not teach me casting until I learned fabrication
because if you mess up a casting you should be able to fix it and
not just cast it over. That makes you pay attention when he tells
you something… Hope this helps…

   Oh ya!!  A burnisher is OK but  using it to cover up pits
is that not just covering up a mistake? 

I could hardly disagree more. Burnished metal is very much like
rolled metal. Considerable pitting can be cleaned out and closed
up by a couple of burnishing-annealing cycles. I often will
burnish an 18 karat casting before doing anything else. More
often than not I can eliminate filing and sanding by burnishing
over the entire surface. I’ll go right to tripoli. Another
advantage is that more burnishing means less stock removal thru
abrasion. The surface has a new grain and takes the highest
possible polish. No science here, just my experience.

Bruce D. Holmgrain
Maryland’s first JA Certified Senior Bench Jeweler


 Burnished metal is very much like rolled metal. Considerable
pitting can be cleaned out and closed up by a couple of
burnishing-annealing cycles. 

Have to agree with Bruce here. The thing to keep in mind is
that there is no such thing as a completely porosity free
casting. Even the best possible casting has some degree of
porosity, even if you can’t see it. Engineers will tell you that
the density of a good casting can be in the high 90s percentage
of the actual theoretical density of the alloy, but you never get
100 percent density. A 97% density is pretty good, but what’s
the other 3%? Air, oxides, shirkage pores, etc. And it can be
much lower percentages than that in some cases. We all know that
rolled, milled, die struck jewelry or metal is “better” than
castings. This density, as well as the finer grain structure,
is the reason. when you burnish the surface of a casting, you’re
creating a surface skin that then has the same density and grain
structure that a die struck piece would have.

Also, catagorically calling all porosity thats visible enough to
see and need burnishing, a mistake, is a nice theory, but it’s
pretty impractical in the real world. Dealing with experienced
professional casters, you’ll still see a little bit of porosity
on many castings. Very few will have none anywhere visible. If
you insist on sending all of them back for redos if you can find
any pits or pores, you’re gonna be pretty unpopular with your
caster. If you do it yourself, then you’re gonna be pretty
frustrated. It’s just the way it works. Especially with higher
karat golds and platinum.

Yes, you want to be as rigorous and methodical and careful in
your casting techniques as possible to get the best castings
possible. But that done, you then also want to use the most
effective means possible to convert those castings into the best
piece of jewelry. Burnishing is a vital part of that process.
It’s also capable of some things that a buffing wheel is not.
You can burnish well, for example, right down into a square
corner. Try doing that with a buff. You can brighten and
sharpen an edge, cleaning it up, straightening it’s line if need
be, all without actually removing any metal. Again, try that
with a buff… Burnishing, like many skills, is something to be
learned. it’s not a cheap trick. It’s not always easy. Neither
is the use of a simple file or a saw frame, when done well.
handled properly, a burnisher can give you effects that are
unique to itself, as well as better metal.

You suggest, or someone did, for example, drilling out and
filling a pit with a soldered in plug when a defect in a casting
is found. When you do that, you’ve introduced the different
color and melting point of the solder, which is almost always
visible (unless you burnish it well). Burnishing a pit doesn’t
just cover it over, it closes the opening down, compressing the
metal around it to fill it in, and litterally closing the large
opening down to an invisible pore. That has a lot more integrety
than a soldered in plug. Won’t discolor, won’t flow when someone
else has to work on the ring later, and doesn’t use up expensive
solder. There are, of course, pits too big to burnish, where
some sort of filling is needed (actually welding/fusing the plug,
instead of soldering it in, is better, if you can do it) but
when you can work over the surface to clean it up, instead of
soldering and welding it, you’ll have a better product in many

By the way, dont forget that there are many ways to do this. A
rub with a burnisher (and there are many shapes, sizes, and types
of burnishers too) is only one. You can forge the metal with a
hammer, planish a surface with a hammer or hammer handpiece or
chasing tool, bead blast with glass beads (which have a
burnishing/hammering action in addition to creating a texture),
or tumble polish with steel shot. All will serve to compact a
castings surface.

Peter Rowe