The Process of Glass

Types of Glass Art


  • reacting
  • techniques
  • bubbles
  • wraps
  • optic molds
  • gold and silver leaf


  • process
  • coloring
  • frit
  • bar
  • opaque
  • transparent


  • equipment and techniques
  • functions


  • fusing
  • slumping
  • casting
  • kiln
  • hot

The Process


Glassblowing is a beautiful process to watch in person. The heat of the fire, dance of the teamwork, and the noise of the tools and equipment make watching the creation of a new piece a fascinating, visceral experience.

We will take you step by step through the process of glassblowing, describing the various techniques along the way. Carlyn Ray is the glass blower; she is also known as a gaffer, a term borrowed from factory work, meaning a person who creates or finishes pieces. Carlyn has been blowing glass for about 15 years and will make this look easy. Her team of artists and assistants are essential to her work and will be helping out.

This is our melting furnace; it contains about 500 lbs. of molten soda-lime glass. The temperature within the furnace is about 2100⁰ F. The furnace is fired with natural gas.

We start out with a blow pipe that has a hole that runs its entire length; it is hollow. All the irons are made out of stainless steel. We chill the skin of the glass a little bit on that stainless steel marvering plate it acts as a heat sink. We also squeeze the material out off the tip of the iron where we can inflate the glass.

This is when we put color on the piece when we use color bar. The ball of color is called a color drop. The colors are heated and once the pipe stops turning, the color literally drops on the piece.

If we want the color swirled, we use friction to twist the colors up. After it is shaped and smooth, we let it cool until it becomes hard and brittle. This enables us to go back to our melting furnace and gather a second time without this first bubble collapsing on us.

The molten glass inside of our furnace has about the same consistency as honey. Right out of the furnace, we use a wooden block to shape, center and cool our glass simultaneously. We always use fruit woods like apple, cherry or pear wood because of the material’s grain pattern, density, and resin content. The wood soaks and is constantly dipped into a bucket of water. Water creates a thin pocket of steam between the wood and the glass; stopping the hot glass from sticking to the wood as well as slowing down the burning of the wood.

Inflating hot glass does not require tremendous air pressure. It’s a medium breath, one to three pounds per square inch of air pressure is plenty to take care of the inflation. To remove the bubble, we create a neckline with a tool called Jacks. This line will become the top and lip of the piece.

To keep our piece hot, we continue to go in and out of the glory hole (reheating furnace) which is usually around 2,300 degrees. We can tell when the glass gets to the desired temperature by touch. Once the glass reaches the desired temperature then we can continue to shape the glass until we move to the next step.

Hot glass sticks to hot glass so we can add bits of glass, handles, and decorative elements. We use various steel and graphite tools to shape these additional bits.

We transfer our piece from the hollow blow pipe that we started with to a solid punty iron. We use a small amount of molten glass on the end of a rod as a glue. The molten glass sticks temporarily onto the bottom of the piece. This leaves a permanent mark called a punty mark which shows that the piece was hand made.

After breaking off the piece from the original blow pipe, the piece is very sharp and jagged. We melt these sharp edges with heat, a technique known as fire polishing. Once the glass gets hot enough to shape, we use tools, centrifugal force and gravity.

In the final heat, in pieces such as our signature butterfly bowls, we make the most dramatic change without touching the piece at all. The material softens with the heat and we begin to spin the piece. As we spin faster and faster, centrifugal force pulls the glass out and gravity creates the organic folds along the lip.

If glass cools too quickly and drops below 900 degrees it will crack. We put our pieces into annealing ovens that sit at 950 degrees and cool slowly until the glass reaches room temperature.

Once the piece is cooled, then we can flatten and ‘cold work’ the bottom of the piece. Cold working uses a series of different diamond pads, wheels and belts. We use different grits until we take it gradually down to a nice smooth surface.

COLORING Examples:

Glass color is usually created by mixing metallic oxides into the raw clear glass. For instance, Cobalt creates blue and Iron creates green glass.

scientific: Glass that is colored by (1) impurities in the basic ingredients in the batch or (2) techniques of coloring glass by one of three main processes: (a) using a dissolved metallic oxide to impart a color throughout, (b) forming a dispersion of some substance in a colloidal state, and (c) suspending particles of pigments to form opaque colors.

Frit is crushed up pieces of colored glass. Using frit can achieve striations, swirls, or stripes in the glass. Hot glass is rolled on top of the frit and the bits of colored glass stick onto the surface like sprinkles on an ice cream cone. Once the frit is applied to the surface, the glassblower can keep the spots or use friction and twist the spots of color to create a spiral.

Unlike crayons, when you mix frit together the colors do not blend, there is still a ‘spot’ of color. But a yellow transparent color on top of a blue color will make green.

Color which comes from a bar gives a cohesive look, unlike the spots from the frit. Bar is usually applied early when the glass is a small bubble. As more glass is added on top of the bubble, the color is spread larger. The amount of color used is dependent on the density of color desired and the size of the piece.

<Photo of Bar>

There are three color companies which sell glass color Reichenbach and Kuglar from Germany and Gaffer from New Zealand. Each company has different hues and specilities, but the main colors are offered by all.

There are different types of color.

Opaque see opaque examples
Opaque color is where you cannot see through the color. When you mix two opaques together the color is separate and does not blend.

Transparent see transparent examples
Transparent color is where one can see through the color. Transparent colors can mix to create different colors. So if a blue and a yellow were combined, a green color would form between the two colors.

For fabricated glass and combining the hot shop glass in the kiln with various projects, we use sheet glass from System 96.

System 96:

Because the way to make the colors is with different metal oxides, specific metal oxides will react with other metal oxides. Many colors are known as ‘reactive’ or ‘reducing’ colors and will both react with the environment or another color. If the glassblower finishes the piece in a ‘reducing’ atmosphere, he/she can pull the metallic oxides to the surface and create a shiny look, often associated with “Tiffany Glass”. Browns can look like metals and whites can look like an opal shell, but this is only achieved when the colors are on the surface of the piece. If the color has clear on the outside (encased) then the metals cannot come to the surface to create this shiny look. Also some colors react with other colors creating a halo of another color where the reaction is. Sometimes this reaction color will be brown, blue, green, or even almost create a spider affect.


Creating bubbles:
Bubbles can be created in glass from either adding baking soda to the glass before a layer of hot glass placed on the outer surface of the bubble. This baking soda creates tiny gas pockets which create bubbles.

Another way to create controlled bubbles is with a mold called a pineapple mold which looks like a small grenade. When the bubble is blown into this mold, the little spikes pierce the glass creating divits. These digits capture air when the next layer is added to the surface, thus creating a pattern of bubbles.

Body wrap are when extra glass is wrapped around the body of the piece. These body wraps can either be controlled in a spiral or as a ‘wacky’ wrap having a more organic look.

Wraps can be melted into the glass to create a coloring technique.

Wraps can also be applied and left on the surface of the piece to create texture.

Lip wraps can be added to the lips of pieces to create a different color just on the top of the piece. No machine can create a lip wrap, so when you see a different color on the edge or a piece, you know the piece has been hand-made.

Rip Raps can be added onto pieces after they have gone into an optic mold. When a bubble goes into an optic mold and a wrap is applied on the peaks of the glass, it is just touching on those specific areas. Once heated, the glass shrinks where it isn’t touching and becomes spots where it was attached to the glass.

Optic molds
Optic molds are aluminum cast molds that glass blowers use to gain texture, change up color patterns, or create an end shape.

To create ridges on a pieces, the bubbles is blown into an optic mold and then shaped.

Optic molds can also disperse color. If a green is placed on top of a white color and then the bubble is placed in the optic mold the color is pushed into the ‘valley’ and then stretched out where it peaks giving it a beautiful color affect. If this is twisted and then done again, a scaled or crosshatched look is created.

The same is true when a wrap is placed around a piece before it goes into the optic, the wrap becomes zig zagged .

Glass has a memory and remembers the thick and thin areas. If a plate is spun out after it has been blown into an optic mold, the edge will have a ruffled affect.

A few metals are compatible with glass because of the shrink rate of the different materials.

Gold and silver leaf are often added in sheet form to the glass and it creates an shiny surface and depending on the thickness or amount of gold or silver, the look can be subtle or intense.

Adding copper leaf with a layer of clear glass on top usually creates blue bubbles.

The metal copper can be used in glass if worked quickly and is sometimes used when working and assembling multiple small parts on an armature.

Cold working as it sounds, is changing the shape or surface texture of glass using tools and processes that do not rely on heat. Cold working methods include grinding, carving, engraving, polishing, sandblasting, and other techniques.

Cold working is usually its own profession in different glass blowing facilities and factories. There are many various techniques and styles which at a high level take strength, skill, and patience.

We are lucky to have Clayton Spaulding who was professionally trained as a cold worker under the Fulbright scholar and professor Chad Holiday who received the majority of his training in Czech Republic.


Flat Wheel
Flat wheel has several different diamond coated disks with various grits ranging from 60 grit to 600 grit. Then there are some pre polish pads and serum polishing pads. A cold worked uses the most abrasive pad necessary first and then grinds down on each pad until the desired polish is on the bottom. The flat wheel is usually used to achieve a flat surface such as on the bottom of a vase, bowl, paperweight or sculpture.

The belt, like the flat wheel, has several different grits including a cork belt to achieve a rounded edge. Belts are used to round out an edge.

Lathes come with several different diameter wheels at different grits to achieve a round spot on the bottom of a piece or to create a texture called battuto.

Hand Grinding
Many artists place grit on a piece of window glass to maintain control of the piece and achieve optimal results if a piece is highly delicate and would not tolerate the high speed of the flat wheel.

The wet tile saw uses a continuous diamond blade to cut the glass. There can be different blades to cut different types of glass. Usually after the glass is cut, it then needs to be polished on the belt or the flat wheel.

The dremmel is used to engrave a piece or also to create a hole in the piece. Different attachments to the dremmel can also allow the cold worker to grind down small areas to a polish and or bevel the edges of flat surfaces after being used on the flat wheel.

Bowls and Vases
Most blown pieces are cold worked on the bottom so that they have a uniform flat surface. Most often they are ground down an several different grits until the surface becomes smooth.

Holes can be drilled, with care, into the glass pieces.

Kiln Forming

Glass can be formed in kilns and ovens to achieve various looks and techniques.

Glass fusing uses heat bonding to combine different sheets or pieces of glass together.

Using heat and gravity, art glass can be shaped over and/or into molds in a kiln to create an almost endless variety of forms.

Color for fusing and slumping projects we use Bullseye primarily.


View the casting color options.

Glass fills up a mold and creates the negative of the mold. The mold can be made out of numerous materials, the most common being plaster/ silica.

Hot Casting
Hot casting is ladling the glass from the furnace into the mold.

Kiln Casting
Where as kiln casting involves measuring glass and filling a reservoir or the actual piece to heat up to melting temperature and slowly fill the mold.


Flameworking, scientific glassblowing, and lamp working are all the same term for the same technique. There are different types of glass that flame workers use that have different properties, but the technique for the both are very similar.

Flame workers use an oxygen and propane mixed torch and hold the glass rods and tubes into the flame to heat up to a workable temperature. They are able to blow, shape, and sculpt the glass into several different shapes.

Flame working is used to create artwork, including beads, figurines, marbles, small vessels, Christmas tree ornaments, and much more. It is also used to create scientific instruments as well as glass models of animal and botanical subjects.