BIRTHING THE MOLDS...

GRB Bells recently participated in our VIVA [Vashon Island Visual Arts] Spring Tour the first two weekends of May. [Our Holiday Tour is the first two full weekends of December.]

As part of the studio's presentation I demonstrate wax injection, one part of the process of the bells' manufacture which I am capable, within the constraints of time, to demonstrate simply. I am thus encouraged to explain here the process of making the mold into which the wax is injected.

Here are the castings made from my original wax carvings for several designs plus their clappers. I call these the "masters" & I securely archive them in order to be able to remake any of the rubber molds which might break or wear out. They are also the best form of copyright, since the molding process will shrink the design slightly & all bells made from them will be smaller. 

You see them sitting upside down on their "sprues", which are the rods which were the channels through which the molten metal entered the temporary plaster mold to make the casting. A bell has at least two pieces -- and the clappers must be made separately, of course.

This group includes The SEAHORSE Bell with its unusually complex, three-piece clapper on the left. [The two bells on the right are the SUFI SURF & the CLOUD PALACE Bells]

This is the raw silicone rubber, which is soft & resembles a dense putty. It comes in strips protected with peel-able plastic on both sides. I cut it to size with scissors & pack it around the master in an aluminum mold frame, with the sprue touching its interior side. At this stage I must begin to think "inside-out" as I work to fill the negative space around the bell with the positive rubber.

When the mold is filled I label it with a thin aluminum or brass tag into which I emboss its name with a stylus. The mold press has two electrically heated platens between which the mold is sandwiched. A heavy screw with a large handle tightens to press it all tight. 

Under that pressure its heat of 350 degrees 

vulcanizes the rubber in about an hour.

The result is a solid block of harder rubber completely enclosing the master, squeezing a slight excess, which insures that all the details of the master have been captured. It shrinks a bit as it cools, freeing itself from the sides of the mold's interior. 

I trim the excess with scissors & peel out the tag, 

leaving the name permanently as part of the mold. 

Next comes the difficult part! I use a scalpel to very carefully cut the block apart to free the master, while also making "keys" to secure the fit when the mold is put back together.

It is fascinatingly puzzling to dance between thinking positively about the negative! It requires bringing the cuts from the bottom of the sprue ever closer to the still invisible master, prying the dense rubber apart with the help of a hook mounted to my desk. It is important to land the cut at the best place on the design to make the mold function well, both to promote the escape of air pushed ahead of the molten wax & for ease of removing the cooled wax.

The mold stretches & wants to snap closed. I must use brute strength of one hand while keeping the other facile enough to aim the blade cutting delicately into narrow-sighted space dancing between positive & negative space...

These photos show the process arrested by being held open with toothpicks... Each piercing in the design must be cut cleanly so as to efficiently re-close, recreating that detail in wax. 

I cut down from around the skirt of the bell to create a core which is pulled from the interior of the master, with another tricky part involving the clapper loop which clings, being filled with rubber in the top of the bell's interior, difficult to reach with the blade. Even with a collection of tricks over years of experience, I often still struggle with this part of the process!

Below you can see that core sitting-up in the center, atop the left & right half of the mold, which shows the positive wax which was injected into it. 

Outside are the halves of the second mold containing the 3 clapper parts.

The wax injector is a heated pot filled with wax under about 5 pounds of air pressure. 

Near-liquid molten wax is injected into the sprue of the mold when pressed against its nozzle, thus engaging the pressure sensitive valve behind it.

 Here is a video of an actual injection:

The result is a wax replication ready to be cast into metal to make the bell I will sell.

POLISHING & MOLDING THE MASTERS...

The Open Studio Weekends were happily successful in terms of attendance, pace & sales. I used the castings to demonstrate the process verbally which I can now share from the photographs I've made as I have polished & molded them in the week since.



I spent a great deal of time & care in the finishing processes to develop the "complexion" of their surfaces without disturbing delicate details. Much attention was paid to the interiors, which will help the mold quality as well as sweeten the sound by fining the proportions in a way almost impossible to perceive in the wax.

I can actually hear the resonance now that they are translated into metal... but that is affected unduly by the fact the sprues add considerable weight which will ultimately be gone.

Polished interior surfaces will allow smoother release of the wax injection from the mold...

[Note: Click on the photographs to view at larger size...]



Notice the tidy new buttons replacing those crude ones used for the first casting... These will connect tightly to the nozzle of the injector shown at the bottom of this post, if your curiosity is impatient. They will build that capability into the molds which are next to be made in this series of rather technical processes bringing the designs into production.



I use a silicone rubber, which comes in strips protected by sandwiching layers of slick thick paper which curls as it is peeled off the soft unvulcanized sheet .25 inches thick... it resembles putty in texture. It cuts easily with scissors to fit inside the aluminum mold frames, stacking & mushing around the polished master suspended inside but still connected to the outside via the button & sprue.

Since one cannot write on the silicon rubber with any permanence, I embed a tag of brass or aluminum thin enough to emboss identification of the design, which becomes then part of the surface of the mold during the vulcanization process, which takes place under the heat & pressure between the plattens of this press.



At just above 300 degrees... & all the pressure I can build with the screw... the rubber solidifies into a tough flexible solid block surrounding the master inside.



Out of the mold frame the molds await my attentions with a scalpel to cut this block open in such a manner that it will release the metal master & then fit tightly back together again.



Beginning at the cavity left by the button I follow the sprue into the block with my knife... cutting the keys which will lock the two halves back together. I must "think inside out" as I prepare this solid rubber version of what is negative space in the normal world.

This becomes a birthing process of sort... leaving the space shaped by that master, ready & waiting to become filled, with melted wax this time... again & again... making production copies of this design in wax. A wax which makes the plaster waste mold, as described in the previous post. Remember that a wax is melted for each metal bell, hence: "lost wax casting".



I used toothpicks to keep the springy rubber half cut mold open enough to make the photograph.



The wax injector is simply a tank of molten wax with a tight lid & under pressure from an air compressor or even a bike pump... it only uses about 4 psi. By inserting the pressure sensitive nozzle into the button/receptacle of the mold which is held tightly together with both hands, one pushes to allow the wax to enter & fill the mold. After several minutes to cool & harden the mold is opened to release the wax, which must next be touched up to repair the parting lines left by the mold seams.



The bell mold has three pieces... one pulls out of the core of the bell first, while it is being hugged securely by the outside halves.



Here the molds lay open to expose the injections...



This is the resulting production wax, prematurely assembled for one more portrait of thois stage in the new life becoming the SEA HORSE Bell.

The molds are now at the foundry & I am anxiously waiting for the first prototypes in silver... savoring my anticipation to actually hear its voice at last. Because all these processes change the bell's size & proportion due to shrinkage, from hot to cold in both wax & metal, this then holds the final mystery!