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Sandcast Glass - Design, Process and Art


Pouring a Sandcast Glass Sculpture



How is sandcast glass sculpture made?


Sandcasting requires a combination of planning, skill and patience.

A design is carefully considered and then poured with skill and patience. The flow of the hot glass determines the outcome of the executed piece.

Below you will find the various steps involved in this process.








Sandcast Glass Sculpture

The Basic Elements




A cool fluffy mixture of sand, powdered bentonite and water.



Handformed shapes (often in wood) used to create the sand mould.



Ladles of hot glass to fill the mould.



Cooling the glass in a controlled manner.



Sketch Concept of Sandcast Sculpture





Sketching the Concept


Sculptures begin by sketching concepts and by planning colour schemes, inclusions and textures.


The sketches are helpful in organising your thoughts, and determining the dimensions, proportions and often the modular pieces necessary to create a larger image.
(as in the drawing on the left).


Wooden Templates for a Multi-Section Sculpture



Cutting and Fitting the Templates


Templates are carefully planned and occasionally involve the design and testing of several assembled pieces for the final sculpture.

The sections are traced onto wood (solid wood, MDF, etc) and cut with an appropriate saw (band saw, jig saw).

The edges and surfaces of the templates are smoothed and filled with sculptors wax to achieve the right surface treatment. (also see the section on wax features)

If all of the template sections fit well and are balanced, then the glass pieces will also be balanced in the final sculpture.

Also, templates should not have any undercuts which would not allow you to remove the template without disrupting the sand mould (see below).

In the end this will result in pieces of glass that fit together successfully.



Creating a Wax Template Feature




Using Wax to Create Template Features


Sculptor's wax is used for a number of purposes.

First, the wax is used to "level" a template smooth its surface or create a texture.

Wax may also be used to create a sculptural feature onto the template surface that can be pressed into the mould.

The warmed wax is pressed onto the template and sculpted using clay and wax tools.



Applying Graphite to a Waxed Template

Click here or on image to see a video of graphite application




Graphite Treatment of the Template


Templates are often made of wood, clay, wax and found objects.These are often finished with wax (for either consistent texture or smoothness).

To prevent sand from sticking to the template when the mould is created, the template is coated with powdered graphite. This can be achieved by using a brush or cloth to burnish the graphite into the template surface.

The more time spent on preparation the templates, the easier it will be to create successful, tidy glass pieces requiring less finishing (or cold work).

Creating the Sandcast Mould


Creating the Sandcast Mould


I have two approaches to making sandcast glass using a sandbox method or a metal tray method

In the sandbox method - the sculpture is moulded in a large box of sand. After pouring the glass, the piece is just barely allowed to solidify, then lifted from the sand to be placed in the kiln for annealing.

In the steel tray method - the mould is created in a sand filled steel tray. The advantage of this approach is that after pouring, the pan containing the molten glass with sand can be placed directly in the annealer. This is my preferred method for sandcasting.

The inital stages of mould preparation are the same for both methods.

In this tutorial I will only explain the steel tray method in detail. An overview of the sandbox method can be found on the sancast process pages of this site.




Preparing the Sand

The sand used in sandcasting is a mixture of sand, bentonite and water.

The sand can be bricklayers grade - although finer sand allows for a more detailed impression.

Bentonite can be sourced from an agricultural supply centre.

Typically for 90 lb sand (~40 kg) I use about 5 heaping cups of powdered bentonite. This is mixed thoroughly with the dry sand.

Its most important to blend the bentonite and sand before any water is added.

Gently mix the bentonite and sand with a shovel or spade.

It is best to wear a mask when mixing the dried materials because the powedered bentonite creates considerable amounts of dust.



Preparing the Sand



Adding Water to the Mixture

It is important to note that a very small amount of water is required for the mixture - thus be sure to have some dried sand-bentonite in reserve in case too much water has been added.

The amount of water required can vary depending on many factors (your mixture, how wet the original sand was, relative humidity, surrounding temperature, etc).

Add water gradually (a half cup or less for every 20 lbs or so). Add this gradually while mixing the sand thoroughly by hand.

To test the proper amount use the sand toss method (pictured on the left).

1) First grab a fist-full of sand, closing your fist tightly.

2) When you open your fist you should have a mass of sand      that holds its shape.

3) Toss the mass of sand a few inches (5 cm) into the air

4) The mass of sand should completely disintegrate upon     dropping back into your palm.

When this is achieved you have the ideal cool fluffy sand mixture for creating sandcast moulds.



Steel tray method

Steel tray method - The Steel Tray

To create a sandcast mould sand is placed in metal pans or boxes. Most often, inexpensive catering pans (bain-marie pans) are used and can be obtained from catering supply shops.

Alternatively steel pans can be specifically made to fit a range of pieces or more importantly - fit the kiln.

It is also important to note that steel pans should be used (not aluminum, copper).

Also do not use chrome or zinc (galvanized) treated steel because of the dangerous fumes that would be created at high temperatures.


Creating the Sandcast Mould

Creating the sand mould


Select a metal tray large and deep enough to accomodate the template. There should be a minimum of 1 inch of sand below (3 cm) and 1-2 inches of sand from the edge of the pan after moulding.

Fill you metal pan with fluffed prepared sand.

Place the template on the sand and pound the template into the sand with a rubber mallet. At this point you may need to add more sand to the pan to build up the sides of the mould.

Pack the sand around the sides of the template to create a firm impression in the sand. The sand should be particularly well compressed around the edges of the template.


Leveling the template


Leveling the template


During the moulding process, it is very important to keep the surface of the template level.

By using spirit levels, you begin the process by making sure the surface on which you are working is level.

Use the spirit level to check the level of your template - coaxing it with your mallet you adjust the level of the impression in the pan. (note that you need to ensure the table on which you ultimately pour your glass is also level).

Maintaining the level of the will enable you to pour an even thickness of glass.



Templates in Sand after Packing and Leveling




Templates in Sand after Packing and Leveling


In a properly packed mould - the templates are level. The sand is firmly packed around the templates with no loose sand, particularly around the edge of the templates.




Removing the Template from the Sand Mould



Removing the Template from the Sand Mould


To remove the template from the sand mould, the template is gently but firmly nudged horozontally in all directions (i.e. back and forth and then side to side) to create a very slight gap around the template. The template is then pulled straight up out of the sand.

As noted in the template preparation section - templates should not have any undercuts. Undercuts would not allow you to remove the template without disrupting the sand.

Once the template is removed, you now have a mould in which to pour the hot glass.




Finishing the Sand Mould


Finishing the Sand Mould

After removing the template there may be some cracks or displacements of sand at the edges of the sand mould. These can be gently repaired by gently pressing the sand by hand or with a small wooden tool.

Excess sand can be removed by brushing it away from the edge of the mould.

Adding the Carbon Release

Once you have made the impression in the sand you must add a layer of release, to keep the sand from sticking to the glass once it is cool.

This can be done using various methods. One is to lay a light layer of carbon using an acetylene torch. This is done by allowing a "dirty" acetylene flame (no oxygen) to deposit a layer of carbon on the surface of the sand mould. This procedure should be done wearing a mask (sorry, old photo).

Another method is to dust the sand's surface with graphite powder, and some artists spray the surface with a mixture of molasses and water.

I do not use this method because the molasses can interfere and stick to the coloured powders and frits I apply to the sand.

Adding a release layer should be completed before adding any other surface treatment (colours, inclusions, etc.).





Adding Coloured Powders and Inclusions




Adding Coloured Powders and Inclusions


Coloured glass powders and frits are added to the mould to colour the resulting sculpture.

Glass powders are finely crushed coloured glass where Frits are small chips of coloured glass which can be obtained in various grades.

Typically I use frits and powders produced by Kugler, Zimmerman, Gaffer or Bullseye.

Other surface colors can be obtained by using jeweler's enamels. These powders are very fine and create a glaze-like surface on the glass.

The frits and powders are typically placed in the mold after it has been carbonized. These colourants can be added using sifts, tea strainers, fingers - any approach to give the desired image.


A Collection of Cut Glass Inclusions


Inclusions add another dimension to the piece and can add to the narrative within the sculpture.

Glass inclusions can be cut coloured glass shapes or pieces of glass thread or cane. Inclusions can also be made of copper, brass, bronze or steel in solid, wire, foil, or mesh forms.

The inclusions can either be placed on the surface of the mould or can be placed between the layers of hot glass, as the glass is ladeled into the impression.

Regarding the use of inclusions please note that when glass inclusions are used - the glass type must be compatable with the batch of glass being poured.

The compatability is related to the relative expansion coefficient of varying types of glass. The coefficient of the inclusion and the molten glass must match.


Adding Coloured Powders and Inclusions

Adding Coloured Powders and Inclusions

The inclusions can either be placed on the surface of the mould or can be placed between the layers of hot glass, as the glass is ladeled into the impression.

When placing an inclusion between layers of molten glass its normally best to place the inclusion where it will be fully encased in glass and not (for example) placed too close to the edge of the mould. This helps avoid cracking in the piece.

Its best to experiment and have fun with colours and inclusions.


Pouring Molten Glass


Pouring Molten Glass

Ideally glass should be poured from a clean steel ladle when it is at a temperature where it runs very freely. This is often at a temperature considerably higher than that used to blow glass.

After gathering the glass the strings and threads which follow the ladle should be immediately cut with glass sheers by an assistant.



Pouring Molten Glass

Pouring Molten Glass

One should pour away from ones body into the mould as soon as possible to allow as much of the glass to be poured from the ladle as possible.

When the pour is nearly completed the ladle should be tilted to allow a very thin thread of glass to form above the piece - which can be cut with glass sheers - by an assistant as near as possble to the glass surface.

In the Annealer


In the Annealer

When the mould is filled with hot glass it is time to take the piece to the annealer. Using the steel tray method the entire container is loaded into the annealer.

The glass (in the sand) remains in the annealer long enough to slowly return to room temperature. This timing in the annealer can range from a matter of hours to a number of days. This length of time is determined by the dimensions and total mass of glass in the piece

Please refer to Henry Halem's "Glass Notes" for detailed information on how to calculate an annealing cycle.


Cleaning and Finishing the Piece

Cleaning and Finishing the Piece

After the piece has been annealed, loose sand can be removed from the glass surface by using a wire brush. The piece can be cleaned by soaking in warm water to wash off any residual sand and graphite residue.

If required (for leveling, etc.) the piece can be further cold worked on a linisher, flatbed grinder or cut with a diamond saw.

Any further embellishment can be done to the surface for example sandblasting, engraving, etc.





Multi component pieces or pieces that are attached to metal frames or ave additional non-glass components can be assembled using silicone caulk.

I normally use a commercial grade, water resistant, clear or translucent silicone caulk. I have found that this forms a very strong bond when there is a tight seal (without air pockets) between the components.



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