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PROGRESS SEQUENCE. Small Skull

A PROGRESSIVE ILLUSTRATION OF

KILN CASTING

SMALL, LEAD CRYSTAL GLASS SKULLS.  

The following is a low tech, backyard casting sequence from a small sculpture studio nestled in isolated, bush clad hills of New Zealand’s Northland.

 

Mother Mold

Looks like something ready to go in the bin?

This is the casing or ‘Mother Mold’ which supports the rubber inside. In this instance it is made with fiberglass for strength and durability. Often made with gypsum, ‘Plaster of Paris’, for convenience.

Plaster, short lived and fragile compared to fiberglass.

Mother Mold Opened

Opened up, the rubber ‘skin’ into which wax is poured at 90c, is now shown fitting inside the ‘glass casing. 

Depending on ambient temperature the wax may be cold in 4 hours or thereabouts and ready for removal.

 

Rubber Mold

The catalytic, RTV silicon rubber skin mold for the making of small wax skulls.

Or another medium if such were desired. Polyester, acrylic, cements, reconstructed media, the choices are many and varied.

 

Withdrawing the pattern

Here the ‘master’ is being withdrawn from the rubber ‘skin. This silicon rubber is a very strong, tear resistant, flexible substance and when designed well for such a mold as this will be capable of innumerable reproductions before deterioration renders it unusable.

 

Extracted Skull

The master pattern released and the rubber ready for wax.

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SMALL, CAST WAX, SKULL

The quality of a wax casting is purely a personal criteria. Here particular attention was focused on the master before the rubber mold was made. Any unwanted blemish on the master would be also on the subsequent wax castings and require unnecessary time in the cleaning up before plaster molding. Or if not dealt to in the wax stage then eventually in the cast glass.

Small, Hand Held, Wax Skull

A clean cast in wax with minimal fettling.

Sprued Wax Skull

Sprued and cupped ready for the plaster molding process.

Wax Skull Mounted With Cup & Sprue

Seam and handling damage requiring attention prior to plaster molding.

Cast Wax Skull Sprued & Cupped

 

Cast Wax Skull to Fettle

Closing in on the most pertinent ‘dings’!

Evident in the upper portion of the image …. A finger nail mark gouged out in the enthusiasm when removing the wax from the rubber!

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FETTLING THE WAX SKULLS

Fettling Small Wax Skull

The flame is burning and wax skulls are ready to clean up before investing in plaster mold.

 

Touching up and finishing Wax Skull

Quick spots of hot wax to fill marks and the odd blemish from handling. The selection of dental  wax working tools assist in speeding the process.

 

Parting line to cleanup

On these small wax skulls this is the only part line and is quite easy to remove. The gouge from finger nail enthusiasm now filled and firm enough to dress back.

 

Finished Wax Skull ready for plaster molding

Finished and almost ready to mold up in plaster.

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PLASTER MOLDING OF THE WAX PATTERNS.

The elementary mold mix is one kg of gypsum, one kg of silicon flour to one liter of water.

 

Pre Coat Wax Skull for Plaster Molding

Critical attention applying this pre-coat of molding plaster is crucial to eliminating air bubbles on the surface of the sticky wax.  Any bubbles caught here will be on the subsequent cast glass and require tools and time to remove.  

Wax Skull Plastering for glass cast

Attention…          quickly…. before the plaster starts setting.  

Wax Skull Covered with 1st coat

As soon as that all important initial film is covering the wax pattern and air eliminated a repeated pouring of the still liquid plaster mix builds up the inner layer for the final molding.   

Wax Skull Pre-coat for Investment

The wax skull now covered with the pre-coat of molding plaster

Pre coat of mold plaster

In container for filling with plaster investment….

 

Plaster Encased Wax Skull

Invested ….. Wax encapsulated within the plaster mold matrix….

 

Invested Wax Skull for Casting

Ready to dewax by steaming out.

 

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STEAMING OUT OF THE WAX SKULL

 

Steaming out the wax skull
Steaming out the wax skull

 Steam being directed into the openings of the plaster molds to melt out the wax skulls.

 

Closer view of applying the steaming out process
Closer view of applying the steaming out process

 A closer view of introducing the steaming process showing the stalicmites and stalictites of molten wax building up.

 

Showing the dewaxing of the Small Skull Molds
Showing the dewaxing of the Small Skull Molds

 

 

A closer detail of the steaming out process.
A closer detail of the steaming out process.

A detail showing the wax base still in place at the initial introduction of the steam pipe.

 

A close up of the dewax sequence.
A close up of the dewax sequence.

The mold now clean of wax leaving a cavity in the form of the wax skull. Almost ready to prepare for glass and kiln.

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CLEAN & EMPTY PLASTER MOLD 

 

Dewaxed Plaster Mold for Small Skull.

Dewaxed Plaster Mold for Small Skull.

Steamed out, clean and waiting glass.

Extreme care to prevent contaminants from falling into the skull cavity.
 
The Appropriate Volume of Glass to Fill the Skull Plaster Mold

The Appropriate Volume of Glass to Fill the Skull Plaster Mold

 In this instance a 1 kilo billet of ‘Rhubarb’dichroic Lead Crystal is the required volume of glass to cast this Small Skull.
Appropriate Measures of Glass For Casting

Appropriate Measures of Glass For Casting

 A hammer to break the crystal into appropriate weights for relative molds and patterns. Hand held in tough leather gloves and covered with news paper to shield from flying splinters.  Or displacement methodswith unknown weights are the best alterative to work out volumes required.

 

Loaded Lower Level of Kiln Ready for Firing

Loaded Lower Level of Kiln Ready for Firing

The lower level of this particular kiln used for  Kiln Casting Glass  is now filled with plaster molds of various patterns. Each with the appropriate amount of glass gently place in the resevoir .

 

This lower level is overlaid with the kiln shelf.

This lower level is overlaid with the kiln shelf.

Kiln shelving being set in place to support the upper level of plaster molds for
Casting the Lead Crystal Glass.

 

The upper layer of Kiln Loaded Ready to Turn on.

The upper layer of Kiln Loaded Ready to Turn on.

All fully loaded, the lid ready to drop and program the control computer for this firing of

Casting Lead Crystal Glass Skulls

With the accompanying plaster molds of other patterns a full week will be required for this sequence of stages to complete the cycle for a successful cast. Under the extreme conditions within the kiln during firing any small oversight in the preparation of these molds could result in disasterous consequences. 

Now the seemingly long wait!!    Patience !! 

 

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Six days Later

 Fired & Ready to Open the Cast Glass Molds

 

Fired & Ready to Open

Fired & Ready to Open

Upper and lower levels now cast and ready to break open and see the results of this firing of Lead Crystal Glass 
The lower level of Kiln Cast Glass
The lower level of Kiln Cast Glass

 

Skull removed from Kiln and now to be broken open………
 
The precoat of plaster evident as a separate layer in the mold matrix.

 

 

 The outer plaster breaks away quite readily from the inner precoat layer

 

 

 

 

 

Cracks in the pre coated plaster cause ‘flashing’. Thin veils of glass bleed into the fracture making for more clean up time.

Can occur by numerous causes.  A couple of common ones are the wax expanding when warming up through the steaming out process and moulds too wet when placed in the kiln and the temperature ramped up too quickly causing the trapped moisture in the plaster to boil with no way to escape.

 

 

Thin, fragile veils (flashing) of glass showing through the fractured plaster matrix.

Final lifting off of the remaining plaster and a quick rinse under the hose…..  

Washed off plaster mold residue and now to cutting off the sprues and dressing. 

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DRESSING OFF THE CAST GLASS SKULLS

A selection of diamond tools and silicon carbide to finish these small Lead Crystal Skulls.

 

Cutting off the Glass Sprue.

Cutting off the Glass Sprue.

A 10 inch, sintered diamond, trim saw quickly cuts off the sprue.
Diamond Cutting the Sprue

Diamond Cutting the Sprue

The water cooled diamond saw makes short work of removing the glass sprue on these small skulls.
Sprue cut off the Skull

Sprue cut off the Skull

  The detached sprue to be recycled for a cast another day. The remaining stubb on the rear of the skull to now be dressed back .
Mounted Diamond Wheel

Mounted Diamond Wheel

A 7″ sintered diamond, 220 grit, grind wheel mounted on a point carver system.

 

Initial Grinding on the Diamond Wheel.

Initial Grinding on the Diamond Wheel.

Initial Grinding & Finishing 

Wet Grinding on the Diamond Wheel

Wet Grinding on the Diamond Wheel

The Diamond Wheel is also run with water acting as coolant and lubricant.

Micro-Motor Handpiece

Micro-Motor Handpiece

A 50,000 rpm Micro-Motor hand-piece using a selection of diamond points to dress back ‘flashing’ and other imperfections on the surface of the Crystal Skull.
Note the ‘bubbles’ of glass in the eye sockets which have to be ground away.

Hand tooling the Skull

Hand tooling the Skull

Final Hand grinding of the skull prior to sanding and finishing.
Again water is the coolant and lubricant which is fed through the brass fitting to the work area on the surface of the glass. 

Final dressing off of the Cast Skulls.

Final dressing off of the Cast Skulls.

Final sanding performed on a 5″ inflatable drum sander mounted on the Point Carver system.

  

Final Sanding

Final Sanding

Steady pressure on 220 grit, wet & dry, silicon carbide belts remove the harsh diamond marks.
Notice the glass ‘bubbles’ in the eye cavity is still to be ground out.  

Finished!!

Finished!!

A small, hand held, Kiln Cast, Lead Crystal Skull finally finished.
The matt texturing from a light sandblasting imparts a deep glow.
Blue Lead Crystal Skull

Blue Lead Crystal Skull

Many colors are these made in.