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How To Slump Bottles - A Step By Step Guide

What is bottle slumping?

Bottle slumping is a process in which glass bottles use gravity and heat from a kiln to change the shape of the bottle. Bottle slumping has a range of possibilities and different shapes and the best thing is that you can use old wine bottles or similar, so no raw material costs. The bottle slumping process can make a number of different practical use pieces, such as trays and dishes. Beer bottles also make great spoon rests or can even be formed into a clock! Slumping molds can also be used to make some unique pieces of art.

In basic terms, the bottle slumping process involves the bottle laid over a mold on the kiln shelf. The bottle is then placed in a kiln at up to 1300 degrees Fahrenheit. As the glass is heated, gravity pulls it down over the mold. Once the bottle is formed into your desired shape, it is cooled (annealed) and brought back to room temperature to dry and harden.

how to slump bottles


What do you need for bottle slumping?

Bottle slumping is a fairly straightforward process. The main thing you will need is a glass kiln that is suitable for firing to a temperature in excess of 1500 degrees or higher. You will need to consider that not all kilns will be able to fit a bottle in them. Some are too small to accommodate a bottle and a mold, so you need to consider this when buying your kiln.

You will also need something for the bottle to sit on so that it separates from the surface, whether that's the kiln shelf or the mold. To be sure that your bottle does not stick to the kiln or the mold when removed, you will need a glass separator, or you can use primer which is painted directly on to your shelf or mold. Perhaps the simplest material is fiber paper.

You will also need the raw material, the glass bottles. You can use any old bottles, such as beer bottles or wine bottles - it all depends on what you want to make. You need to make sure that the bottles are clean and dry and that any labels have been removed. To remove the labels, soak the bottles in hot water overnight with some oxy-clean or similar and the labels should peel off easily.

Finally, and optionally, you will need a mold to create your desired shape. You can purchase a variety of different mold shapes or you can make your own using bisque. The important thing to remember is to cover the mold with kiln wash, glass separator or fiber paper. Alternatively, you can simply place the bottle directly flat on to the shelf but again you will need to make sure kiln wash or fiber paper is used to avoid sticking when the item is removed.


Bottle slumping firing considerations

There are many firing profiles for bottle slumping and much depends on the size and shape of your bottle. Slump glass can be a trial and error experience - sometimes the kiln manufacturer guidelines are not suitable as they do not always account for larger bottles or the type of glass. It's best to undertake a test piece or two, in order to master your program and get the process to work well for you. Generally the firing takes approximately 9 hours.

several slumped bottles


Step by step guide for bottle slumping

As mentioned previously, the slump glass firing method is relatively straightforward. The most important part of the process is in the preparation. Here is a step by step guide to slumping your glass bottles:

1) Place the bottle over your mold or flat on the kiln, ensuring that it is not directly in contact with the surface of the kiln or the molds.

2) Fire your kiln and raise it to a temperature of approximately 1100 degrees. Raise the temperature up slowly to avoid cracking your mold, usually by 500 degree increments. You should try and hold at this temperature for at least 10 minutes, so that all the bottles in your kiln reach this desired temperature.

3) Ramp the temperature up slowly by 250 degree increments, in order that the bottles heat evenly. If you want to create a slight concave form then you may hold the kiln at the temperature at 1300 degrees for less or more time, dependent on your desired outcome.

4) When the bottle has slumped, it will start to visibly collapse. Once you are happy with the shape that you like, you should start to cool the temperature.

5) The next step is called annealing. If you fail to do this step carefully, you may find that your bottle cracks once it has completely cooled. Simply cool your kiln to between 800 and 1000 degrees and hold it for an hour. This will remove any stress in the glass from its rapid temperature increase.

6) The final step is to cool your kiln right down to room temperature and allow your glass bottle to harden. A large bottle will inevitably take longer than a smaller bottle.

two slumped bottles


Important safety considerations

The high temperatures involved in slumping means that the kiln and glass can get extremely hot. Make sure that you wear heat resistant gloves when dealing with your kiln and wear safety goggles to protect from the heat.


How to flatten/slump bottles without a kiln

While traditional methods often involve using a kiln, it's possible to achieve flattening/slumping of a bottle without a kiln.

Firstly, make sure the bottles are completely dry before proceeding. Cut a piece of kiln paper or fiber paper to fit the size of the bottle. This paper will help prevent the glass from sticking to the surface during heating.

Place the kiln paper on a heat-resistant surface, such as a ceramic tile or metal baking sheet. Then, place the bottles upside down on the paper. Preheat your oven to a low temperature, around 200-250°F (93-121°C).

Carefully place the bottles in the preheated oven. Allow them to heat gradually for about 10-15 minutes. Once the glass starts to soften, it will begin to sag and flatten.

Once you're satisfied with the shape, turn off the oven and let the bottles cool down slowly inside. Avoid sudden temperature changes, as this can cause the glass to crack.



When looking to slump glass bottles, the key to an effective outcome is to have the necessary equipment in place. You will need a suitable glass kiln that is both large enough to accommodate your project and that can also get to the temperatures required. Soul Ceramics have a range of glass kilns suitable for any glass or bottle slumping project.

You will also need effective slumping molds should you wish to create a specific shape. Again, Soul Ceramics can provide advice on this should you need it.

As long as your bottle is washed and prepared properly, then your glass bottles or beer bottles will form a variety of fantastic finished goods, suitable for your own use or as part of a commercial venture.