Streaky bubbles on surface of waxes

I’m at my wits’ end with my wax injector.

When I inject wax into molds of flat, smooth-surfaced objects, I get
weird streaky bubbles on the surfaces.

It almost appears as if the bubbles have been rolled or pushed as
the wax entered the mold, causing the streaks. Casting waxes with
these streaks produces castings with long shallow voids. Filling the
streaks with disclosing wax leaves marks on the castings. I have a
regular casting job that involves making a couple hundred flat
surfaced castings every few months. Every time I have to do one of
these jobs I waste several pounds of injection wax while trying to
get enough good waxes to fill the order.

I thought at first that maybe the wax pot had an air leak, allowing
air to get in as it was being injected.

I’ve gradually replaced every gasket and moving part on my
hand-pumped (note–no air compressor) Kerr Injectomatic II wax pot
that can be replaced, including finally replacing the entire nozzle

After the nozzle replacement, the streaky bubble problem
disappeared-- for a while. Now it’s back, worse than ever. I spent two
hours pulling waxes today and got ONE good wax.

I’m about ready to throw the danged wax pot away and buy a brand new
one, except that I can’t really afford to do that.

I keep the wax as close to the manufacturer’s stated melting point
as I can, and keep the pressure as low as possible. But I have tried
using hotter wax, cooler wax, higher pressure, pre-heating the mold
with a hair dryer, chilling the mold in the freezer, powdering the
mold with corn starch and various combinations of all of the above.
Nothing has helped. This happens with quite a few different molds, so
I’m certain that it’s not just the mold that’s causing the problem.
Any mold that’s fairly flat gets the streaky bubbles.

What could be causing this, and how can I fix it?

Kathy Johnson
Feathered Gems Jewelry

When I inject wax into molds of flat, smooth-surfaced objects, I
get weird streaky bubbles on the surfaces. 

Causes can be, not enough air vents, vents not in the right place,
allowing air to be injected into the mold at the very beginning of
filling the mold. When you pull the plunger up, as you start pushing
the plunger down, make sure wax is flowing from the injector. Flat
pieces are the hardest parts to cast…

Richard Hart G.G.
Denver, Co.


I can’t say that I know everything when it comes to wax injection,
because we are not a production casting facility. We do a lot of
castings, however, and use a lot of rubber molds which we make here,
from both rubber strips (vulcanized) and room-temp molds.

When you mentioned all the things you were trying to get a good wax,
I didn’t see a reference to your air vents. Can I assume you have
air vents cut into your rubber molds with a sharp scalpel? Air vents
connecting the outer edge of the mold cavity to the mold’s exterior
are vital to get the trapped air out of your mold so the liquid wax
can fill the mold completely. Our air vents are powdered lightly
inside with a light dusting of cornstarch, and the mold cavity then
blown off of the excess powder before injecting. The tiny particles
of cornstarch help hold the vents open slightly so air can pass
through the mold when injecting.

We DO NOT use a spray mold release (which would gum up the powder in
our air vents).

I sometimes see molds made by others that have incomplete ( not cut
to the outside edge of the mold ) or even missing air vents, which
can cause incomplete waxes from the mold.

I can’t make a suggestion for you about your hand-operated wax
injector, but I would recommend an air-compressor powered model. We
use an inexpensive Harbor Freight air-brush compressor to power our
injector, which works well for us. In this way, we can absolutely
control our injection air pressure, which is vital. Ideal air
pressure ( as well as wax temperature ) varies with each kind of mold
you’re shooting.

We are also finding our students prefer a carvable injection wax, so
they can modify their injected wax models easily if desired, but a
wax that isn’t too brittle to handle.

Good luck!
Jay Whaley

Jay can you say what type of wax you consider to be carvable? I love
making modifications after I make a mold. So I am always on the
lookout for a ‘carvable’ injection wax that I might not have tried

Thank you, Angela


Obviously the best waxes to carve are those hard carving waxes,
designed to be sawn, filed, burred, and scraped.

Some of my students still want to modify the wax models they
reproduce from their original castings. We are still experimenting
with injection waxes to see what works best.

I have long used Plastowax, which is very durable, injects well, and
is carvable, somewhat. A few months back, as a concession to my
students wanting a more carvable injection wax, we emptied out the
wax injector and replaced the wax with Rio’s “Carvable Injection
Wax”. It injected well, carved great, but was quite brittle. I
accidentally dropped a wax model a student had been laboriously
hollowing out, and it shattered on the wood floor. OOOps! Playing
chemist, I mixed about 25% Plastowax with the Rio Carvable, which
made the wax carvable, but less brittle.

Now we are playing with Eurotool’s carvable injection wax, which I
think everyone likes. For burring out injection wax, I highly
recommend the 3-finned wax burs, as ones with more fins load up with
wax far too easy.

Unfortunately, the injection waxes do not have the transluscent
qualities true carving waxes have, making them difficult to hollow
out in front of a strong light source.

I’m interested to see what other jewelers are using for carvable
injection wax.

Jay Whaley

Hi Angela,

Many times I have to adjust and re-carve cast waxes. Relief Wax, Wolf
by Ferris works really well for me, when small amounts are melted
onto the wax mold piece. Can even be worked with burrs. Hope it works
for you too.



I hate carving injection waxes. My solution is to inject blue carving
wax. Nozzel bored out, temp run up higher, presure up to 25 PSI. Use
care, I clamp the mold plate together and wear gloves, that stuff is
HOT. Much more of a challenage to inject but it is usually possible
and worth the effort.

Demand Designs
Analog/Digital Modelling & Goldsmithing

I’ve been trying some of your suggestions over the past couple
weeks. The biggest one was emptying the wax pot, cleaning it out and
replacing the wax with Plast-o-wax.

(The Plast-o-wax is MUCH easier to see than the purple Freeman
“carve-able purple” stuff!)

Changing the wax helped a little bit–I still got a lot of streaky
bubbles, but not quite as many. I tried adjusting the temperature
and pressure of the pot a few times and got an occasional random good
wax, but still had about a 90% failure rate. I kept notes of what
temp and pressure combinations I’d tried.

Then I had to leave the project for 3 days to go do something else.
I left the pot on as I always do.

When I came back and pumped it back up to the last pressure I’d been
using on Thursday, suddenly the thing is working almost perfectly.
I’m getting a small streak every once in a while, but I’ve gotten
quite a few good waxes back to back from both the old mold and the
new one I made last week.

I’d say my failure rate is down to maybe 10%-15% right now.

The only thing that changed from Thursday to Monday was the local

Can atmospheric/barometric pressure affect the output of a manual
wax pot?

Kathy Johnson
Feathered Gems Jewelry


Holding the wax at working temperature for that period of time will
alter the molecular weight distribution of the wax. The higher
molecular weight portions of the wax will degrade first, leaving a
lower median molecular weight and a narrower distribution.

Clearly, the alteration you achieved is a positive for you, while
it’s likely the finished molding will be more brittle than if the wax
was only briefly heated.

In your case, as long as the waxes burn out well for casting, you
don’t need to blush at the idea you just upset all the wax chemist’s
calculations. Burn baby, burn!

Mark Bingham
Fourth Axis