What Is Kilncasting? Tips, Tricks & Techniques

Kilncasting is the process of creating an object out of glass in a kiln. This is achieved by heating cold glass above or inside a mold until it gets hot enough to melt, flows and fills the voids within the mold.

Kilncasting is a relatively common process in glass making, but perhaps the most difficult part of the process is creating the mold. When glass casting, there are two types of molds to choose from: open-faced or closed/semi-closed.  

An open-faced mold creates a one sided reverse-relief, whereas a closed or semi-closed mold enables the creation of full glass structures.

What equipment will you need for glass kilncasting?

Wax

It is best practice to create your design in wax before building a mold around it. The wax can be easily manipulated using a range of common tools and can create interesting textures and shapes.

Plaster & Silica

The actual mold itself can be made using a combination of plaster and silica. Mix equal parts of plaster, silica, and water together until the mixture resembles heavy cream. Plaster makes the mold hard and resistant and silica is used as it can withstand the heat.

Scales

Scales will help you to weigh your glass and gauge how much glass you will need for a particular project.

Kiln and kiln furniture

The kiln is perhaps the most important aspect of your equipment. A kiln needs to be large enough to fit your mold in and also have the capacity for melting the glass into your mold and annealing. Controlling the temperature to get the kiln to the right temperature for both the melting and hardening process is vital and so electric kilns are certainly the recommended way to go.

Kiln furniture is also important to provide the relevant spacing between pieces to ensure that they do not stick together.

Coldworking tools

The finishing stage of your project will involve coldworking tools to finalize your project, smooth and polish it. Common items to use are tools such as a grinder or belt sander to provide polish to your finalized piece.

What is the kilncasting process?

Design your piece

It’s best to sketch out your project before you start shaping the wax into the form that you would like, but don’t create anything too big in order that the finished piece fits within the kiln. You should also ensure that you don’t make your mold too thick. A glass piece in excess of one inch thick can take over 24 hours total in the kiln. Thicker pieces can lead to kiln firing times that can stretch into weeks, which is clearly not practical. 

Next you need to shape your design in wax using any type of wax that is easily molded and malleable. You should make sure to create a wax reservoir to your design to enable the glass to flow through.

Make the mold mixture

At this point it is vital that you make sure that your work area is well ventilated, and wear a respirator when working with dry investment. Make the mix of silica and plaster and then build a simple wooden box around your wax model to ensure that the mold is secure. Pour the mixture into the box and let it sit for 30 minutes.

A good tip is to try knocking on the table when you transfer the plaster mixture into the mold as this will knock out any air bubbles. You need to avoid any bubbles because they will create holes in your final piece.

Melt out the wax

The best way to melt wax out of a small mold is using a microwave. Try and prop the mold up and place something underneath to collect the wax. Heat carefully until all the wax has melted out.

For larger molds, prop on a larger support frame with a bucket underneath to collect the wax. Use a wallpaper steamer to melt all the wax from the inside but be sure to wear gloves as the steam and hot wax can be extremely hot. Once the wax has melted out, rinse the mold so that any excess wax is removed and then leave to dry completely.

Measure out the glass

The best way to measure the amount of glass you will need is to use water. Pour the water into the mold until it is full and then pour this water back into a container, weighing how much water you used in grams. Multiply this weight by 2.5 which will give you the amount of glass you will need.

Insert the glass into your mold

Fill up your mold with as much cold glass as you are able. If you can’t fit it all in then suspend a container with a hole in the bottom above the mold which enables the glass to drip into the mold in the kiln.

Fire the glass

The temperature for your kiln really depends on the size of the piece. After your glass is melted, you must slowly bring the temperature down to anneal it. As mentioned previously, the thicker your piece is, the longer it will take to anneal. You must wait until the piece has cooled to room temperature before it can be removed.

Tip: check out our range of bead annealing kilns.

Clean your piece

When the piece is completely cool, the mold should easily break away. Clean any excess mold from the glass by soaking it in vinegar and using a brush to gently remove any excess away.

Coldworking

Coldworking is a key element of the process, which ensures that any rough edges are removed and the final piece is polished to perfection! A grinder can help to achieve the perfect finish.

Check out our extensive collection of glass kilns to create your glass casting

A kiln that controls the temperature is perfect for any kilncasting project. Electric glass kilns can modify and manage the temperature to ensure that the project can be sufficiently heated and then cooled to ensure annealing.

At Soul Ceramics, we have a range of high quality electric kilns, glass casting kilns, and wax burnout kilns which can accommodate small or large projects. Using a kiln to experiment at different temperatures will ensure that you can create your perfect project.

If you would like to know more about our range of kilns or you are looking to invest in a kiln for a hobby or as part of a business, please do not hesitate to contact us and we’ll be happy to advise you on the most suitable kiln for your project.

Additional resources on glass fusing

• An overview of glass fusing tools, supplies and equipment
• Common glass fusing issues and how to solve them
• How to fuse glass at home