Bubbles problem with lost wax casting

Jewelry Discussion
1

My wife and I own a jewelry store and we are expanding into doing our
own casting inhouse. We bought all of the equipment from making the
molds to casting and finishing. We started with white bronze because
it was cheap to practice and now we are casting in silver. Our main
problems is the waxes. There are bubbles. and some of the castings
in both the bronze and silver have holes. We bought the wax clean but
it seems to make it worse. If there is a bubble the wax clean caves
it in.

Does anyone have any advise or tricks for us ? We are using pink wax
and have a top fill wax injector.

Thanks,
Buck and Angie

2

The most likely cause of bubbles in the wax is that the wax is too
hot.

You want it just hot enough. Even 2 or 3 degrees hotter and you will
start seeing problems.

If the rubber molds are not allowed to cool enough between shots,
that can also cause the same trouble.

Moisture in the compressed air supply can also cause bubbles. This
is usually from failing to drain your compressor and not having water
filters in the lines.

There is not much to it when you get all the little variables sorted
out.

But that is easier said than done.

Stephen Walker

3

For me, the injection wax makes a HUGE difference. If it is not the
correct wax for you and your setup, it is nothing but problems no
matter what you do.

Are you having bubbles in the wax or getting pits or other problems
in the casting? If bubbles in the wax, try a different wax, use
surfactant/releases in your molds, try different wax pot
temperatures. Heat your molds a bit as sometimes bubbles are water
vapor from very small amounts of moisture in your molds. What are
your molds made of? Are you using releases (do you need them, not if
silicon but even with silicon molds, sometimes a release helps).
There are just SOOOO many factors here, , and your info is
not very complete. What wax are you using? Is it in fact injection
wax? Are the bubbles open to the surface or “just under the
surface”? If just under the surface, they may not be any problem at
all, if open at the surface, fill them with a wax pen or soft wax.
Again, there are so many potential areas to look into…

Where are you? I am W. of Seattle about 1.5 hours and a ferry ride.
If close, come over and we can talk. If not, can you post pictures
somewhere? Want to call me, 360.681.4240 and we are in Pacific Time
zone. Also how are you “working the investment” Vacuum or not? What
type? Burnoutee? On and on…

Call if you like.

john dach

4

Hi Buck,

So, if I understand you properly, you’re getting voids (bubbles)
within the volume of your injected wax, which is causing pits in
your finished castings, correct?

Could be a whole host of things, unfortunately.

(A) which wax are you using? “Pink” isn’t much beyond a color. Every
manufacturer has their own recipes, and colors. Some waxes are more
prone to bubbles than others. Personally, I’ve got a big stash of
Sierra Red that I’m still working down. That was a Swest product,
years ago. Don’t know if anybody’s still making it, but I’m quite
fond of it. It might be worth looking at your wax. Also, the
’carvable’ waxes tend to have more trouble with bubbles (in my
experience, such as it is) than the straight injection waxes.

(B) what temperature are you melting the wax at? You’d be surprised
how twitchy wax can be. For my rig, a difference of 1 degree (F)
makes a noticeable difference.

Talk to whoever made your wax, and find out what they recommend.

© how long are you letting the pot pre-heat? Some of them take 6-8
hours to get up to temp and stable. You can get wax after 45 minutes
or so, but the temps will be all over the map. You have to wait for
the whole load to fully melt before you can get anything repeatable.
(My trick is to put a timer on it, so it kicks in at 0’dark thirty,
and it’s nice and warm whenever I get around to it.)

(D) for the truly ridiculous, you can install up a vacuum rig on
your pot, so that you can pull vacuum on it after it all melts. So
as to vacuum degas it, and pull all the trapped bubbles out of it.
I’ve never tried it, but I’ve seen rigs like that on sale, so
clearly somebody thinks it’s a good idea. That’d be the last
thing I’d try, (due to cost) but it is an option. (Vacuum as in
vacuum pump, not shop-vac. If it were me, I’d frankenstein a line
from the vacuum pump I use for investing, rather than buy a whole
’nother pump for it.)

For whatever that all was worth.

Brian

5

Hi Buck and Angie,

Pink was seems very soft when I work with it. I like to use the aqua
blue injection wax. My friend likes to use the purple injection wax.
Both waxes have more plastics in them and they seem to mold better.

Good luck!
Ken Moore

6

We have a stash of Serria Red too. Is/was a GREAT injection wax. The
"replacements" are not up to snuff as far as we are concerned, but
our foundry waxes have changes a lot is the last couple of years,
changes to the negative. I am sitting here just shaking my
head…

john dach

7

Dear buck & Angie,

I have used the New York City Pink wax for over 20 years. I would
not change.

Check you wax temperature. It should be no more than 158 f. You can
do this with a candy thermometer. There is a hole for it in the top
of most wax injectors it drops in. You can recycle dud waxes as long
as they are not dirty.

Each mold needs to have vent lines cut from the model out to the
side of the mold. The wax pushes the air out. If the air cannot
escape you have trapped bubbles. Look at your waxes to see if there
are parts that have the same spot with bubbles. That is a good place
to cut a vent line.

Rubber molds work well with a little spray silicone. Silicone molds
work better with baby powder. You need an air jet to blow out extra
baby powder after you apply it.

When you inject, hold the mold on the nozzle for longer times and
look at the waxes. Sometimes a longer injection will fill and
decrease the bubbles.

Hand holding may leave you various wax injections with some people
having different hand strengths. You might try a mold clamp. Again,
hold it on the nozzle longer to decrease bubbles.

Good luck,
Todd Hawkinson

8

Hi

in an old casting book, lost in space between workshops, they
recommend hand pouring for waxes.

Any wax will do this.

Time intensive, but better quality than injecting wax. However the
best waxes I have seen are from hot silicon pancake moulds spun on a
centrifuge made from an old record player, at 78 rpm.

Wax stays liquid and is forced into the moulds by centrifugal force
till the mould cools.

Although taught how to cast, I was told to send waxes to a
professional caster.

Yes extra cost but high quality castings, every time. Don’t have to
spend a few grand on casting machine etc.

Money better spent on metal and gems.

Casting has so many potential complicated problems when done in
house makes me think hand making, what I do, has many advantages. I
guess it depends on volume of the same design.

That said I want to try steam casting, some time soon.

However the responses on Orchid will give you many options and clues.
Richard

9

Hi Richard,

in an old casting book, lost in space between workshops, they
recommend hand pouring for waxes.

[snip]

Although taught how to cast, I was told to send waxes to a
professional caster. 

Yes extra cost but high quality castings, every time. Don't have
to spend a few grand on casting machine etc.

[snip]

That said I want to try steam casting, some time soon.

Hand pouring waxes using gravity can work well too, but you need to
think a little differently about how the wax flows. The trick is to
get a high definition gravity pour wax (awesome stuff if you can get
it).

I do agree with sending waxes to the casting house for economic
reasons, you just pay for the final casting, you don’t pay for the
button. Casting equipment for gravity pouring is very modestly priced
(assuming you make some of the equipment).

Regards Charles A.

10

Hi

in an old casting book, lost in space between workshops, they
recommend hand pouring for waxes.

Any wax will do this.

Time intensive, but better quality than injecting wax. However the
best waxes I have seen are from hot silicon pancake moulds spun on a
centrifuge made from an old record player, at 78 rpm.

Wax stays liquid and is forced into the moulds by centrifugal force
till the mould cools.

Although taught how to cast, I was told to send waxes to a
professional caster.

Yes extra cost but high quality castings, every time. Don’t have to
spend a few grand on casting machine etc.

Money better spent on metal and gems.

Casting has so many potential complicated problems when done in
house makes me think hand making, what I do, has many advantages. I
guess it depends on volume of the same design.

That said I want to try steam casting, some time soon.

However the responses on Orchid will give you many options and
clues.

Richard

11

Helpful hints on investment casting: troubleshooting casting problems

DEFECT - CAUSE - SOLUTION -

Cracking - Quenching too soon - Wait 15-20 minutes

Cracking - Metal cast too soon - Increase casting temperature

Cracking - Flask too cold - Increase flask temperature

Cracking - Incorrect sprueing - Modify sprueing

Cracking - Contamination of gold or alloy - Refine metal

Cracking - Oxide build up in metal, over-use - Refine metal

Cracking - Hydrochloric acid di-vesting - Use alternative di-vestor

Incomplete fill - Metal too cold - Increase casting temperature

Incomplete fill - Flask too cold - Increase flask temperature

Incomplete fill - Insufficient vacuum - Check vacuum for leaks and
seal

Incomplete fill - Wrong speed on centrifugal caster - Adjust speed

Incomplete fill - Insufficient burn out - Modify sprue

Incomplete fill - Incomplete burn out - Use proper burn out schedule

Inclusions in castings - Sharp corners or bends in sprueing - Round
out sharp corners and bends

Inclusions in castings - Crucible old and deteriorating - Replace
crucible

Inclusions in castings - Oxide build up in crucible - Clean or
replace crucible

Inclusions in castings - Foreign particles or oxides in metal -
Refine metal

Inclusions in castings - Investment erosion or breakdown - Follow
investment manufacturer’s mixing instructions

Brittle prongs on castings - Improperly alloyed metal - Pre-allay
gold and master alloy

Brittle prongs on castings - Flask temperature too cold - Increase
flask temperature

Shrinkage prorsity - Incorrect sprueing - Sprue to heaviest area of
casting

Shrinkage porosity - Inadequate sprueing - Use larger sprue or
multiple sprues

Shrinkage porosity - Flask too hot - Use lower flask temperature

Shrinkage porosity - Castings too close to sprue button - Leave 1"
space on tree above main sprue button

Gas porosity - Metal overheated - Reduce casting temperature

Gas porosity - Inadequate burn out - Increase top end burn out time

Gas porosity - Inadequate air supply during burn out - Assure oven
has good air supply & exhaust

Gas porosity - Flask too hot - Reduce flask temperature

Gas porosity - Scrap reused too many times - Refine metal

Gas porosity - Too much oxygen on torch flame - Use reducing flame
when melting

Gas porosity - Investment residue on remelted scrap - Remove
investment residue before remelting scrap

Rough castings - Flasks not cured before burnout loading - Let
flasks set 1-2 hrs. before burnout loading

Rough castings - Incorrect water-powder ratio in invest. mix -
Follow investment manufacturer’s instructions

Rough castings - Flasks heated too rapidly - Follow investment
manufacturer’s instructions

Bubbles/nodules on castings - Investment not mixed, vacuumed or
vibrated sufficiently - Follow investment manufacturer’s
instructions

Bubbles/nodules on castings - Vacuum pump not working properly -
Check vacuum pump oil level and

Bubbles/nodules on castings - Wax patterns not coated with wetting
agent - Coat wax patterns with wetting agent

Andy The Tool Guy

12

I like this guy, (Richard). You mentioned hand pouring wax and steam
casting in the same post. Now we are cooking with fire!

As I am new to goldsmithing and so far self taught, I am astounded
at the the lack of on how lost wax casting can be done
without electric hogging burnout ovens, vacuum machines, and
investment that comes with instructions that require 17 different
temperature holds for 17 different time periods.

There has to be an easier way to cast. I know that the reason for
the equipment is probably for consistent results and to have less
finish work, but Iwonder if there is possibly a less finicky
investment formula to be more energy efficient? The steam casting is
easily explained and works well, butwhat did the first goldsmiths
use as investment?

Rick Powell

13

For casting a production line I have found that it is more cost
effective to job it out. For quick needs better to do it in house.
Thus a casting machine in house is needed.

After moving to Panama and seeing the quality of castings here I have
bitten the bullet and invested the $50,000 to buy the equipment
needed to do quality castings. For over 40 years I have not needed to
go this route. As i lived in the U S.

Enjoy living in a country that has good casting companies that you
cast and send work out too at a reasonable cost. Keep designing and
making what you love.

14

Hi Rick,

Depends on where and when, but the ‘ancient’ investment involved
clay, straw, and animal dung. (Generally horse, in areas where there
were horses. Smells least bad.) Having had horses at one point, I
was moved to try it. Wasn’t tremendously effective, and certainly
nothing like modern investments. Smelled wonderful burning out
too. Quantitatively worse than cuttlefish. Also MUCH more labor
intensive and finicky than modern investment. (out of four molds I
think I had ?one? that didn’t crack, spall or do something else
dire.)

Four molds was most of a day to prep, and then another half day to
fire. I could have had four flasks invested and waiting for burnout
in under an hour with modern investment, without half trying.
Depending on the rig, you could do that in 30 minutes if you were
serious.

Modern investments have become noticeably less fussy even in the
last 20-30 years.

If you’re looking to make a point of being ‘lotek’, knock yourself
out. (Downwind of me.)

If you’re looking to make jewelry, I’d spend your energy elsewhere
than trying to re-invent a covered wagon in a world that’s long
since moved on.

Regards,
Brian

15

Well Rick, it is well and good to use “old time methods and
materials” but part of evolution is using newer setups too. Ditto
goes for almost any area of ones life today. You could shop wood for
cooking the wild meat you harvested, and for the fire to keep you
warm tonight. Take a cold washing, not hot water (out of the
pressurized piping system in your house) and take the dirty water
out to water some of the garden you are growing (no
supermarkets/food purchasing), no canned items, no frozen, no
restaurant. How far BACK do we want to go and live every daye Yes
the kilns use power, electric or gas, but so does your car, your
lights, heating your home, etc. Older methods are great to know
about and to try, but to make a living using them in todays business
systems is a bit nuts. Fine if you want to struggle but nuts.

As to needing “17 different temperature holds for 17 different time
periods”, you need to get a different investment. As to an
easier way to cast, that is what “pre mixed, formulated, tested,
tried and true” investments are for. Ditto with temperature/timer
controlled investment kilns are for. As to casting, repeatable
alloy/metal mixtures give repeatable and consistent castings. Do you
not think that with all of the 1000’s of folks dealing with all
sorts of investing/castings processes that “they” would have by now,
with todays technology, have come up with some of the most
successful, repeatable casting processes/materials mankind has ever
had availableee?

Some of the “first investments” were horse or other non ruminating
animal manure or cow or other ruminating animal manure mixed with
chopped straw alone with sand and clay and water. Long burnouts,
lots of failures, poor alloys (inconsistant) and lots of chopped
wood or dug out of the ground coal. Easier?!?!?!?!?!? I don’t think
so, but growing all of your own food isn’t easy either. AND, where
did the “first gold smiths” get their gold, files, vises,
magnification units and, and, how the heck did they solder anything?

Don’t know where that all came from, but it is out now and I do feel
a bit better!!!

Good carving, molding, waxing, casting and finishing, how ever you
choose to go about doing it!!!

john dach

16 
can be done without electric hogging burnout ovens, vacuum
machines, andinvestment that comes with instructions that require
17 different temperature holds for 17 different time periods.

We mix the investment, vacuum, pour, vacuum the flask. You can do
without vacuum butit’s WAY better. Let it set at least an hour,
usually more like 6. Put it in the kiln, turn it on to 6 1/2
(Neycraft right now), 6 hours or so later we turn it down to about 3
and we cast an hour later or more. Been doing it that way for 30
years without any problems, ever. Other problems yes, burnout
problems no.

17

Hi

can’t find the link to steam casting but google it and there is a
metal work teacher

who has some great info. About forty bucks set up.

Richard

18

Thanks Andy for sharing this info. wish I had had it 40 years ago.
Will share it with others I know here in Panama.