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Saving a hole-y casting


#1

I’m teaching myself wax carving, silver casting & soldering, and I
still have a lot to learn. I cast my first original wax carving in
silver last night. It came out with several holes in it. I’m not sure
why this happened–it was carved from a solid block of “perfect
purple” wax, and I didn’t see any air bubbles when I was checking the
thickness.

But the big question I have is, how can I salvage this piece and get
a halfway decent mold of it so I don’t have to start over from
scratch? My thinking is, if I can get a mold of it, I can fix the
problems better on a wax copy and make another mold of it once it’s
repaired.

I’m still lousy at soldering–I tend to melt things. The piece
has some delicate sections right near where some of the holes
appeared, so patching the holes with solder is out of the question.
What else can I use to fill in the holes at least long enough to get
a cold mold (RTV) of it?

–Kathy Johnson
Feathered Gems Jewelry
http://www.featheredgems.com


#2

Not knowing what the piece is or just what kind of “holes” you have,
the following may or may not be useful. If these are small enough you
may be able to fill with silver. Drill into the hole with a drill
large enough to give you a clean sided hole,insert a tight fitting
wire, clip off and solder. You will (almost) never be able to fill a
hole or a gap with solder alone. If however you have a BIG , rough
looking void you may have had incomplete burnout. Sometimes a pit can
be repaired by cutting a hemispherical depression with a ball bur
and soldering in a ball of the appropriate metal. The ball is made by
melting a piece of metal on a soldering block. Sometimes you can make
a saw cut and fill it by driving in and soldering a tight fitting
bit of sheet metal. Like it or not you’re going to have to improve
your soldering skills and the only way I know to do that is with a
little bit of study and a lot of practice. Of course the same can be
said for casting. With study and practice casting defects decrease
dramatically. Good luck. Jerry in Kodiak


#3

Well, if you are not good with soldering, then you have several
somple solutions. I am assuming that you are going to want to
eventually melt the metal of your original hole ridden piece, so I
will make suggestions that will burnoff during melt.

  1. You could use the purple wax that you have and melt it into the
    holes. Then smooth off the excess. Use this only if you are going
    to make a cold mold.

  2. If you have a hobby store near by, go and see if they have any
    model putty. The stuff is fairly easy to work and drie s, so you can
    buff it smooth or make adjustments as needed.

  3. There are quite a few 2-part plumber and wood epoxies that can be
    mixed with your fingers, and then tooled after they harden.

  4. Just check with your local hardware store or Lowes and
    HomeDepot. I am sure they have more than one product that can help
    fill your holes. Just make sure that the product you buy does not
    have any metal fillers, which would decrease the purity of the
    original metal if it is melted down for a re-cast.

Silverfoot-
www.firescale.com


#4

You can fill the holes with a soft wax and smooth it over or an
epoxy and sand it down. Then make your RTV mold. Frank Goss


#5

If you are going to make a mold of the ring anyway, whether RTV or
vulcanized, why bother filling the holes at all?

Simply make your mold, if rubber tears off (from flowing into the
hole cavities) after pulling your first waxes then so much the
better-- your holes will be filled in in subsequent waxes. If not,
then fill the holes in your injected, second generation wax w/ more
wax. I wouldn’t bother messing around with fillers at all, unless
you intended this item to go into high production.

Andy Cooperman


#6

Hi Kathy, I would like to talk about the problem that caused the
original pitting before talking about methods of fixing the existing
problem. Pits or bubbles in the casting can be caused in several
ways.

  1. There could be bubbles in the wax that pop when the item is
    vacuum invested. If I am concerned about bubbles in my wax
    assemblies I will pull a vacuum on them before investing them. If
    there are bubbles they will show up and can be repaired before
    investing.

  2. If the burn out is incomplete there can be particles of carbon
    left on the surface of the mold. This will cause indention’s in the
    casting. If the area with the pits is thick enough they can be
    sanded or abraded away.

  3. The combination of the metal and mold temperature is too great
    which causes the silver to absorb oxygen. Either the metal was too
    hot for the temperature of the mold or the mold was too hot for the
    temperature of the metal. The mold temperature is different for
    centrifugal casting Vs vacuum casting. You will find that all
    artist use temperatures that work for them and what works for one
    may not work for another. Normally these type of pits do not show
    up until you abrade some of the silver away. If oxygen is absorbed
    in the silver no amount of polishing with tripoli will remove them
    because they can exist deep in the casting.

If you intended to create only one piece of your design it may be
cheaper to start over and take precautions to prevent pitting in the
next design. Mold making can be pretty expensive. In the future use
a wax that is designed for carving. Kerr makes several grades of
carving waxes that can be filed, drilled, sanded and ground with
burrs. There have been several repair techniques described which
can be used if you intend on reproducing the item. If you plan on
making only a few reproductions of your item doing nothing to the
original may be the best time saver. You can make either a cold
mold or a hot mold from the unprepared original then correct the
injected wax.

If you plan on making many reproductions any of the methods
described in previous posts will work. If you are making a cold
mold almost any method of filling the holes will work. If you plan
on making a hot mold you will have to use a heat resistant method of
filling the holes. This process might require a material such as
epoxy which is readily available at any hardware store.


#7
If you plan on making many reproductions any of the methods
described in previous posts will work.  If you are making a cold
mold almost any method of filling the holes will work.  If you
plan on making a hot mold you will have to use a heat resistant
method of filling the holes.  This process might require a material
such as epoxy which is readily available at any hardware store 

Hi, You can also burn the pits out of the rubber molds that were made
by using your wax melting pen at full power so the tip is cherry
red. do very slow passes over the affected area until it is burned
away. Silicone rubber is more heat resistant to burning, so you will
have to leave the hot tip on it longer than with conventional
organic rubber. This is also how thin areas in rubber molds can be
made thicker… this becomes important when you copy a casting you
originally had no intention of doing and had to do so due to a
pitting problem. Unfortunately, even when you use non- shrink
rubbers, there will still be shrinkage factors… ( non-shrink
rubbers do shrink , but less than other rubbers( about 1%) ) wax from
injecting into the mold shrinks and your metal shrinks in the
casting process… My advice is that when you carve an original wax,
make it a little thicker, stronger just incase you do have a
problem… you can always remove material easier than you can add it
! Daniel Grandi

We do casting/finishing and a whole lot more for designers,stores and
people in the trade. We are an Orchid advertiser.Please
contact us off list at sales@racecarjewelry.com


#8

Fuse it… a little smith torch a fast tip and another torch to
provide base heat. Use a piece of ss and flux then as soon as you
see the surface get red you can move the small torch and ss wire
form a bead and lower it onto the pitted area… careful you ca melt
but if you just concentrated the small hot it will fuse to the surface. Ringman