Kiln Formed Glass

The article describes the basic challenges and the commonly used techniques in kiln formed glass.

 

The article is adressed to the common man. If you have already worked with glass it will probably not be very new.

 

 

It’s fascinating and exciting to watch, as you can see how it’s being formed, and it seems a little ’dangerous’ because the glass is glowingly red and between a 1100° and 1300° Celsius.

Working with kiln formed glass is something entirely different. The artist works with the glass while it’s cold, before and after it has been through the oven. You prepare the glass for example by cutting it in different shapes, using colors, maybe use several layers of glass. Afterwards you’ll put it in the oven, so it can be melted together.

The glass can be bought in plates, and it’s being prepared and cut before it shall in the oven. Here is a round dish being prepared.

 

Mostly the glass needs to go through the oven at least twice. First time to melt each glass piece together and second time to shape it, for example as a dish. It’s necessary to do it these two times, because if you did both at the same time, the glass would run to the bottom of the shape, because of the high temperatures there’s being used.

 

The shaping of the glass happens in a separate process in the oven with lower temperatures than the melting process. The temperatures when you melt the glass together are about an 800° and the shaping is about a 700° Celsius.

 

An oven with prepared glass, ready to be melted.

The final shaping happens by help from gravity in the oven, while it’s closed and you as a rule can’t effect the movements of the glass. It means you’ll have to plan the designs down to last detail before burning – especially if you’re making advanced sculptures.

 

The technique of the kiln formed glass is a 4.000 year old technique which original comes from the old Egypt. The technique has been forgotten in many hundreds of years, before it came up again in the end of 1960’s.

 

 

Glass is a fantastic material. It’s fragile but also very strong.

It’s psychically strong because it can tolerate for examples moisture, sun and frost.

But it’s also strong in its artistic expression. The nature, the colors, the transparency of the glass and the reflection of the light, makes the glass a perfect material to create exciting art. The transparency gives depth, and the reflection of the surface plays with the light. 

Because of the transparency of the glass, there has been created a depth around the eye, which makes the eye follow the viewer. The eye is built in 4-5 layers.

 

There’re also many challenges with glass. Here are some of them:

If you mix different glass, these tensions can come.

Or if you used a lot of other materials - like metal - in your design, it could create tensions. 

In this picture has the glass created a bubble of air, which then has exploded.

It’s always the layer on top which melts first. And because glass is a bad heating device, it takes some time for the glass layer in the middle to melt. It means; when several layers of glass melts together, they melt together on the edges at first. And air is trapped between the layers.

 

A piece of a picture of a glass plate with lots of bubbles.

 

Either you’ll have to accept the bubbles, or you can try hiding them, for example with some colored glass on top.

Different kinds of hardness

Even though the glass pieces you’ll use expose the same, they’re still able to melt at different temperatures. For example does black glass melt before white glass. This can mean that the black areas will grow more…

 

 

It takes time to create art using glass. Hand worked things of course always takes time. But as the glass needs to go into the oven several times, and because it takes time for it to heat down again, it takes many days (at least 24 hours + 24 hours, and that’s just what the small things need) in a oven, before it’s all done.

And it’s not before you’ll open the oven for the last time, you know if the result is as wanted. Glass is a living, unpredictable material, and there can come many different surprises in shape or color. It takes many tries, to get it as you want.

But that’s also the charm of working with glass.

 

To melt the glass together. For example a full-fusing, where the glass pieces melts totally together.

There’s also tack-fusing or relief-fusing, where the layer on top doesn’t melt totally together with the bottom layers.

The cat is relief-fused as the ears, eyes and legs aren’t totally melted together with the white body.

It’s the temperature, how long it’s on its highest and for how long, there decides how much the glass melts together.

Using slumping the glass lies in a shape, and takes after the shape.

It’s the gravity there does the shaping of the glass, as it falls down into the shape.

Here’s a slumped glass plate.

 

A type of slumping is bending. The difference is the shape, and that it often happens with a lower temperature, because there’s less glass lying on the glass shaper, so the gravity happens quicker.

In this technique the glass is softened above a hole in a square of wood, so the middle of the glass falls down the hole and creates a U-shape.

 

This is made by sagging.

 

With this technique you’ll work with the glass when it’s liquid, as an exception to earlier writing. At first some glass is being melted in the oven. You can for example make a zebra pattern by using bars of glass, black and then white.

 

An example of combing where I with an instrument have torn in the glass two places.

 

When the glass is liquid, you can open the oven, and with an instrument tare in it, so the pattern gets a bit more exciting. You can use the result as it is, or just use bits of it, and put it together with another design. 

 

 

 

The molding is also a technique there’s used in kiln formed glass. In basic it’s about melting glass, so it fits into a shape.

Sand molding

In this technique you’re molding in sand, where you have made a shape in the sand. It’s the most free form of molding, and it’s very easy. You’ll just lay pieces of glass in the sand, and melt it in the oven. 

If you’ll turn the pieces of glass vertical, and don’t totally melt it, it will look like the fish above.

 

The result will always give a rough structure, and you can choose if you want some of the sand to melt together with the glass on the surface. This will happen, if you don’t put something to separate the glass from the sand.

Open gypsum molding

At first you’ll have to make a shape in gypsum, for example a shape to make a mask. Because of the talent of the gypsums it can be very fine and very detailed.

Like with the sand molding you’ll fill up the shape with pieces of glass, perhaps in different colors, and then melt the glass in the oven.

The glass which in the oven turns upwards will always melt to be flat, like the behind of the fish above.

Closed gypsum molding

In a closed gypsum molding you can make 3-dimensionel molding, as there is no need for very much of the product to be flat.

A closed gypsum molding is for example a gypsum ball, there's hollow in the middle – for example as the shape of a broccoli - which shall be filled with glass. It’s more difficult to work with the closed gypsum molding than the open, there’re a lot more challenges.

The gypsum form can be made by a shape which looks like how you want the result to look. It can be a real broccoli or a dancing woman made by beeswax.

You’ll built more and more layers of gypsum on the real broccoli or the wax shape until you’ll have a gypsum ball. Afterwards you’ll burn the gypsum form in the oven, where the broccoli for example will evaporate and then leave a hollow room, which will look like the real broccoli. 

A broccoli molding in a closed gypsumform.

 

And then you’ll fill the hollow room with floating glass, by making a little hole you can let it through.

 

 

Other techniques / effects

Basically you'll create your design as a mixture of shape, colors and patterns / figures. Though many artists also want to give their designs a little something else, and there’re lots of possibilities to do that.

Here’s illustrated some of the possibilities:

There’s a thin layer of metal in the colors of the rainbow. The colors play with the light, and give life to the plate.

Using of other materials and chemicals

There exist a lot of different metals in a lot of shapes, which you can use. Some of the metals change colors if there’s oxygen present during the burning, for example copper, which turns blue. But you’ll have to be careful with use of metals, because it can also create tensions in the glass.

Some of the metals can also be very expensive, and very hard to work with.

The appearance of bubbles and pretty colors can happen by using oxides, as manganoxyd which turns purple during the burning. Colorless bubbles can be made by baking powder. 

A plate where the blue in the middle is created by koboltoxyd.

 

Pearls and glitter can also be useful.  

Aftercare of the glass

The glass can be polished, graved, abraded or you can drill holes so it can be hung up.

Sandblasted glass can be matt and velvety on the surface. You can cover some of the glass, and that way decide where there shall be sandblasted, that way you can make patterns. 

This plate is partly sandblasted.

 

Some artists like to combine other materials with the glass. Then you often glue the stuff together after the burning.

 

Even the using of tools can be handy working with glass, which has made a Danish glass artist famous.

 

 

When the glass comes out of the furnace, each glass sheet gewts a number. If you cut a piece of the glass, and melt it together with any base glass, which is subsequently measured for voltages. This ensures that each glass can be used with other colored glass from Bullseye.

 

 

 

As mentioned before, coldgalss is many things. It’s a broad area with lots of possibilities – and challenges. And that is only some of it!

I sense that kiln formed glass is going through a development these years, and there constantly comes new techniques and new designs. I often look at other glass artists, and I’m always very impressed by the creativity and quality many of the coldglass artists have.