Designing a Pot Melt

The Pot Melt process creates a colorful glass disk. Compatible scraps of glass are heated in a clay pot inside the kiln.

The glass when heated to a high temperature flows from an opening in the bottom of a clay or stainless steel container. This flowing thick syrupy glass substance will result in a spiral or circular pattern.

Each piece will be a unique piece of art and impossible to duplicate. These disks can then be used intact or cut up and used in fusing projects.

Always wear protective eye wear when looking inside your hot kiln. High temperature gloves are recommended when firing glass to such a high temperature. Cotton fabric clothing is recommended, because synthetic fabrics are extremely dangerous at these temperatures. Try to avoid opening the kiln to peek at the pot melt when it is at 1700F. If at all possible, place your pot melt so that your can observe it through the peep hole.

Three things that will affect the final pattern.

1. The way the glass is layered in the pot. There are different looks depending on how the glass is placed. By standing the glass on end the colors retain some of their individual identity. Laying the colors flat will mix and blend the colors.

2. The size, shape and number of holes in the pot. A round hold will produce a proportioned spiral, while a slot will produce various effects. More than one opening will cause the glass to react like several crucibles are being poured.

3. The height of the pot in relationship to the landing point. When the pot is placed higher, the flowing glass is thinner and the outcome is a finer detail.

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Materials depending on your individual need:

  • Clay pot
  • Chisel, knife, scissors, drill
  • Glass scraps
  • Kiln posts, fire bricks, dams, Kaiser Lee Board
  • Kiln wash, fiber paper, or thin shelf paper
  • Prepared clay saucer, kiln bottom or kiln shelf
  • Kiln
  • Select a pot that will fit comfortably inside your kiln once supported and lifted. Clean and dry the pot in preparation for the melt.

    Enlarge the hole in the bottom of the pot to your desired size. Try using a chisel, knife, a pair of scissors, or drill to enlarge this opening.

    A circular opening will produce a swirling effect in your pattern. Try making a rectangular opening for more of a folding effect in your finished product. A couple of holes will produce an even different look in your design.

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    You will need to build a support for your pot melt. This support can be made using kiln posts, fire bricks, long dams, or Kaiser Lee Boards. The idea here is to build a support that will not only hold your pot with the opening at the bottom being clear and free from obstruction, but also allow the glass to flow onto an open area. I chose to cut up some Kaiser Lee Boards to use for my supports.

    Prepare the space below your pot. If using a clay saucer, the bottom of your kiln, or a kiln shelf, the surface of any of these items will need to be prepared with several coats of kiln wash. Using kiln paper on a pot melt can lead to the paper moving and being stuck in the glass. Pot melts are very hard on a kiln shelf, so try to use an object like a washed clay pot to catch the molten glass.

    Build your support and place it inside your kiln. The pot should be placed so that it is in the center of your support and so that the hole in the bottom of the pot is not obstructed. Make sure that the area below your pot is prepared and not obstructed so that your glass can freely flow.

    Do not put kiln wash inside the pot that is holding the glass. Place pieces of scrap glass inside your pot. Make sure that all these pieces are compatible. Experiment with different color combinations. Try not to use too many dark colors as these can over power your lighter colors. One pound of glass in a four inch pot will give you a disk of about seven inches in circumference. Three pounds of glass will make your disk about eleven inches wide. You can place a piece of clear scrap glass in the bottom of the pot to support your scraps, but this is not necessary.

    Firing Schedule

    Since the pieces of glass in the pot are small, they will heat up quickly without the fear or worry of thermal shocking. Heat up your kiln as fast as possible to about 1700 degrees Fahrenheit. (It is suggested that these melt should only be fired to 1600 degrees Fahrenheit and soak for about 45-60 minutes. This is because firing the kiln to 1700 degrees Fahrenheit can be harmful to the kiln, coils, and the pot.)

    Hold the melt at this temperature until the pot is empty, or you don’t see any more glass flowing from the bottom of the pot. Now turn the kiln down and bring the temperature down to about 1450 degrees and hold for about 15 minutes. This will allow the molten glass to flatten out more. Then lower the dial and bring the temperature down to about 960 degrees Fahrenheit and hold for another 30 minutes. Bring it down at about 50 degrees per hour to about 800 degrees Fahrenheit and hold at this temperature for another 30 minutes. Turn it down again and bring the temperature down at about 200 degrees per hour to 700 degrees Fahrenheit and turn off the kiln. Allow the kiln to cool to room temperature.

    At the end of cooling off period, you will notice that some glass has stuck to the inside of the pot. You can reuse this pot a few more times, but it is best to do so using the same color scheme. Don't put kiln wash on the inside of the pot; you might get pieces of kiln wash in the final melt.

    This schedule is for a 4 inch pot melt. For larger melts holding time for the annealing should be increased to about 60 minutes.

    Pot melts are very hard on your kiln shelf. There is always the chance that it might ruin the actual shelf. For this reason, some people dedicate a separate shelf for doing these melts, or use a mold to melt into.

    Firing schedules are meant only as general guidelines. Kilns will vary and you will need to experiment with your kiln to see what will give you the ideal results. Make notes in your firing log to help diagnose successes and problems.

    Read the section on annealing . This will help you understand the process and why it is a very important step in the fusing process.

    Do some kiln-watching of your individual kiln to see how long it takes your kiln to cool through the annealing zone. Check that time along with the thickness of the glass piece and the manufacturer's published recommendations. It is always better to be safe than sorry . It would be terrible to lose a great looking pot melt because of poor annealing.

    Some reasons that a melt might crack:

  • Uncompatible glass mixed in the melt
  • Foreign particles in melt like clay from pot
  • Sticking to kiln shelf
  • Some things to keep in mind when doing a pot melt:

    1. High temperatures can cause one or more colors to shift their COE a little. Oranges, reds and yellows are more prone to shifting COE than other colors.

    2. Kiln wash begins to break down at these high temperatures so give the saucer or kiln shelf more coats than a normal wash protection.

    3. Stuck glass can cause cracks or breakage, since the glass and saucer cool down at different rates.

    4. Purchase Italian, German or US made pots for this procedure. The ones made in Mexico tend to crack in the heat.

    5. Do not kiln wash the top container that holds your pre-fused glass. The wash will come off and drop down into the melt.

    6. To determine how much glass for a particular size of melt, check out the Pot Drop Calculator .

    7. If kiln wash is stuck to the bottom of your melt, once it is cooled, soak it in some vinegar.

    8. Lower and longer temperatures will help avoid kiln wash sticking on the melt.

    For some different affects try:

    1. Place a clear circle of glass under the glass to be melted and allow the molten glass to flow on to this area.

    2. Try using the pots that have the drainage holes on the side of the pot instead of the bottom.

    3. Use shallow stainless steel dishes instead of a pot and drill holes in the bottom.

    4. Place various colors of stringers and frit on the shelf or in the catching container and then fill up the pot with clear glass. As it pours down it will swirl the colors and leave clear sections.

    5. Use fiber paper underneath your pot for a more textured back.

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