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Flow lines on injected wax models


Hello Orchid,

I have been having problems with flow lines on my waxes, that is fine
lines that look sort of like a wood grain pattern that runs
perpendicular to the direction of the wax flow. It seems to only
happen with thin patterns that have a smooth surface. I have tried
various waxes at suggested temperatures as well as higher and lower
temps without really coming up with an answer. Right now I’m using
"Joe’s New" pink wax from Rio. It was working ok last year but since
I started making new waxes this spring I’ve a poor success rate.
Also, since I have only a hand plunger type injector (not hand air
pump) it’s quite difficult to be consistent with the pressure. So can
anyone tell me the exact cause of this phenomenon? It seems as if the
wax is hardening bit by bit as it flows in causing a line where it
has hardened, and then a bit more flows in and hardens, etc. like
growth lines in a tree. Higher temperatures don’t seem to help,
though neither does lower temp. I try to vary the pressure to
determine if higher or lower pressure is better but it’s difficult
with my very basic injector. Also I am using RTV silicone molds,
don’t know if that makes a difference or not. I’ve never tried rubber
with these patterns. It seems to be a kind of voodoo that happens
with my waxes where if I really need to make a lot of one item I get
a terrible success rate with maybe 1 in 4 waxes being usable, but if
I only need to make a few they all come out perfect. Am I missing
something obvious? Perhaps a better injector, though I don’t have
space or cash for a compressor. How well do the hand air pump ones
work? Your thoughts are appreciated, Thanks.



Most obvious first thing is that there is not enough vents to allow
air to escape. A rubber mold shrinks and makes it more difficult to
get a good wax when the model is thin. Talc and silicone spray
improve success. If you need more help e-mail me off line, would be
happy to advise.

Richard Hart G.G.
Jewelers Gallery
Denver, Co. 80210

Perhaps a better injector, though I don't have space or cash for a
compressor. How well do the hand air pump ones work? Your thoughts
are appreciated, 

The direct hydraulic injectors are very difficult maintaining
consistent pressure. I have one and need a really good reason to do
battle with it.

Air pressure is much better. No compressor is really needed, just a
storage tank and a bicycle tire pump. Injectors don’t use the much
air, just the pressure. Pump the tank up maybe once a day. I’ve used
a 3 gallon tank, an old modified1 lb propane torch tank (probably
broke a few laws), and an air pressure water proof watch tester
(didn’t even get fired for drilling a hole in a $500 machine with
minimal / no permission :-). All worked well, even the little tester.

If possible get a small pressure injector and a tank. Consistent
pressure is one less (major) variable. Then practice. Different
pressure, accurate temperature, and well vented molds. Talc the vents
and avoid silicone sprays on RTV. (seals the vents)

Demand Designs
Analog/Digital Modelling & Goldsmithing


Dear Douglas,

My experience with the kind of flow lines you describe is that they
are caused by a mold that is cold. That is, the rubber is not warm
enough and chills the wax as it goes in.

Typically these go away as you use the mold again and again, thus
warming up the rubber.

Michael Knight


I also use a plunger type wax injector. I am familiar with the flow
lines you describe. Yes, as Richard Hart says, use talc and try
silicone spray. Be sure to put talc into your vent cuts so that air
can easily get through, and try venting more. Speed is essential in
getting good wax into the mold!

What I really have to say is this: not every model is a good model
for making a mold to inject wax. Flat, smooth surfaces are often a
problem, since for some reason the wax gets sticky on the flat
surface where it will not do so if the surface is textured. Perhaps
there is some turbulence created by the textured surface that keeps
the stickiness from happening. The silicone spray may also help with
flat surfaces. But I have started to texture the back of most of my
broad, flat designs. I take the almost-finished metal model and
carefully texture it all over the back by repeatedly applying a
spinning ball bur to create what almost looks like a miniature
planished surface. This also has the advantage of finishing well with
mass finishing techniques. I have actually had good comments from
both retail and wholesale customers on the appearance of this
surface, by the way!

I have sometimes had to re-make a model after trying to inject the
mold I made of it. It can be a learning process. You can go thinner
with short wire-type forms than with sheet forms, it seems. I usually
start with 18 gauge sheet when I am fabricating for a model for a
large pendant (over an inch in diameter), to allow for finishing,
mold shrinkage, and the engraved lines or depressions I may add to
the piece.

M’lou Brubaker
Minnesota, USA’louBrubaker/


After you have injected several waxes, your mold begins to heat up
and can cause problems with fill… Wait a while or cool with
compressed air. If you need to make a lot of waxes, it sometimes
speeds things up to make several molds of the same pattern. When
using the plunger injector, just push with the tip of your extended
index finger. That way you don’t get too much pressure and can
better control it. If you don’t have a clamp, put a metal plate on
each side of the mold and wrap a thick rubber band two or three times
around each end. This provides uniform clamping and the mold can
easily be held with one hand.

Dave Anderson
Erik Jewelers


Hi Douglas,

I’d suggest that the “flow lines in your injected waxes” would have
to be a Temperature issue. I know you stated that you’d tried higher
and lower temps…with no success.

There is more than one way to address this. My first thought would
be that the mold itself is cold/cool and that could cause the wax to
"chill" and possibly leave the “flow lines”. Or that the wax wasn’t
hot enough when injected(that’s my gut reaction), OR a combination
of the two.

I’ve found that almost every mold…and different wax have specific
temps and pressures to get optimal results. That is something that
is only determined with experimentation.

That being said…I’d suggest that you try a higher wax temp. which
will have two effects. One…should allow the wax to flow longer
without the “chill lines” and it will also “preheat” the mold. It
only takes a few “injections” to get the interior of the mold warm
enough to not be an issue. Once that variable is taken out of the
equation…then you just need to “dial in” the proper wax
temperature and pressure for injection.

THE good news is that you’ve gotten GOOD waxes out of the mold
before. So you know it’s doable. ONCE you find out the “perfect” temp
and pressure I’d suggest that you mark that on the mold. IF pre
heating of the mold is ALSO needed… make a note of that too.

I must admit, I’ve never used a “hand plunger” to inject wax… that
could be part of the problem… being able to get consistent with the

best of luck getting better waxes. Let us know what you figure out.
dos centavos, :slight_smile:

Bill Roberts


Hi Douglas,

About the flow lines on your wax patterns from silicone molds. First
off, make sure that the molds aren’t cold.

The silicone fits so tightly, it creates a seal. Try cutting some
very fine ‘whiskers’ on a diagonal from the pattern to the outside of
the mold. (If the cuts are diagonal, you aren’t as likely to crack
the wax when you flex the mold.) With a scalpel, cut a line from the
model to the outside edge of the mold. Now make the cut again, on a
slightly different angle, removing a skinny skinny V of material.
Now the air will leave the mold, and the wax can fill it quicker.

I hope this helps!
Kate Wolf in Portland, Maine hosting wicked good workshops by the bay.


Hi everyone, I’m having some problems with flow lines on my waxes,
where the wax seems to solidify and then flow over itself causing
small lines in the model. I have tried varying the pressure and
temperature without any conclusive results, sometimes they’re there
and sometimes not. Using a flameless smoother works but then my nice
clean lines are lost. The molds are rtv silicone from hand
fabricated 16g hammered filligree mandalas, not too thin to cast but
apparently difficult to make good waxes from. Any suggestions?
Thanks, Douglas


Try heating the molds. Fine work can be very difficult to get good
waxes from any mold, but heating the mold has pretty much "fixed"
the problem. Also a different injection wax might give you relief.
Better air relief in the molds could help, getting the mold filled
faster. If you are using a pot that uses air pressure to move the
wax, make sure the pressure gauge is accurate. If a hand pump unit,
just try all sorts of time dwells, temperature settings and different
waxes. Also with silicon molds, the 2 parts often fit so well
together, the air has trouble being expressed and powdering the molds
can cure freeze lines. There can be so many different things causing
them, in your particular process, , but once you figure out how to
overcome them, clean nd wonderful waxes become second nature
(seemingly). Best of luck on this.

john dach


It sounds like cold wax and not enough pressure.

Have fun and make lots of jewelry.
Jo Haemer