How to flatten glass bottles

How to flatten glass bottles
How to flatten glass bottles

Flattened glass bottles can be an interesting piece of art, a dish for serving your drinks, or a chic cutting board. It is not possible to flatten glass bottles with regular household appliances, but once you have the ceramic kiln to do so, it becomes an easy to learn and fun experience to perform. Remember that if you have an accident with glass, you must call 911 right away.


Part 1 of 3: setting up the ceramic kiln

Flatten Glass Bottles Step 1

Step 1. Purchase a ceramic kiln

Glass needs to be heated to around 815 ° C in order to lose its shape. To get to this temperature, you are going to have to find a ceramic kiln to rent or buy one yourself.

A ceramic oven often requires a new electrical installation installed by an electrician. An oven connected to the wrong voltage may not be able to reach the desired temperatures

Flatten Glass Bottles Step 2

Step 2. Follow the safety precautions

When working with the oven, you should wear gloves and goggles specialized for this type of oven to protect yourself. Wear a mask when handling or cleaning up dust and splinters in the oven and always operate it in a well-ventilated area. Remember that the interior of the ceramic kiln heats up much more than a kiln or a fireplace. Before you begin, read the kiln operating instructions or seek the advice of a professional ceramist or glass artist.

Flatten Glass Bottles Step 3

Step 3. Protect the bottom and shelves

If you neglect this step, shards of glass could damage the bottom of the oven and the shelves while you are heating the glass. There are certain elements that are used to do this and you have to manipulate them while wearing a mask. You should install this protection whenever the glass starts to look distorted, when it is chipping or breaking down.

  • You can buy a glass separator (recommended) or ceramic kiln cleaner (suitable) as a powder that you will need to prepare to get a liquid. Spread at least four coats with a brush and wait for them to dry. Try to get as smooth a surface as possible, as any irregularities you leave there could end up on the glass.
  • Alternatively, you can cut ceramic kiln paper (fiberglass) to cover the shelf. Put some in the oven and turn it on to 760 ° C to blacken the paper which you can then use as protection between the glass and the shelf.
Flatten Glass Bottles Step 4

Step 4. Place the shelf in the oven

The oven shelf should always be above the bottom of the oven to allow air to circulate between the two. Place the shelf supports on the bottom of the oven before placing the shelves on top. When you get ready to work the glass bottles, you will put them on top of the shelf.

Part 2 of 3: prepare the bottles

Flatten Glass Bottles Step 5

Step 1. Make a ceramic mold (optional)

If you prefer the bottle to take a hollow shape like a taco instead of a flat shape, you have to press it into clay to create a mold. All molds should be protected with ceramic kiln cleaner or glass separator, as described in the previous section.

Use special clay that withstands a temperature of 815 ° C or it may melt when you turn on the oven

Flatten Glass Bottles Step 6

Step 2. Clean the bottle and remove the label

Scrub the bottles with hot water and soap or let them soak in a bucket filled with hot water and detergent for several hours. Rub any labels or stickers on the glass or scrape them off using a hard plastic object. Otherwise, if you want to keep the label, melt the glue with a heat gun.

  • Painted labels should be heat resistant, which makes them a great decoration as long as the bottle does not move during heating.
  • To avoid leaving fingerprints on the glass, wear gloves and wash afterwards with isopropanol.
Flatten Glass Bottles Step 7

Step 3. Apply a spray bottle containing devitrification agent (optional)

This product helps prevent devitrification or crystallization of glass which could cause a cloudy appearance. Be aware that not all glasses are susceptible to devitrification and you can prevent it most often by cleaning it. Use the spray bottle very carefully, especially on blue or amber-colored bottles.

Flatten Glass Bottles Step 8

Step 4. Add a hook (optional)

If you want to hang your flattened bottle up when you're done, take a piece of wire and shape it into a hook and then place it in the neck of the bottle. The bottle will close around the wire, so there is no need to hang it.

The best would be to use wire which is resistant to high temperatures. Most wire will do, but the aluminum will melt and the copper and brass can leave marks on the bottle

Flatten Glass Bottles Step 9

Step 5. Avoid the bottle rolling

Put the bottle or mold that contains the bottle on the shelf by laying it on its side. If you think they might roll, hold them in place using crushed glass or small rolls of ceramic kiln paper. This will leave a mark on the back of the bottle, but it's better than having a bottle that rolls around and damages the wall of the oven.

Take extra care to keep bottles with painted labels in place

Part 3 of 3: flatten glass bottles

Flatten Glass Bottles Step 10

Step 1. Heat the oven to 590 ° C

Heat the oven by increasing the temperature by 275 ° C every hour until you reach 590 ° C. This will allow you to heat the bottles.

If you are using ceramic molds, you could use a slower heating rate to reduce the risk of the mold cracking

Flatten Glass Bottles Step 11

Step 2. Hold this temperature for ten minutes

By exposing the glass to this temperature, you can heat all parts of the glass to the required temperature. Pay close attention to the steps below to find out how long you need to keep the oven at a certain temperature.

Flatten Glass Bottles Step 12

Step 3. Heat more slowly to 700 ° C

This time, heat the oven without exceeding a temperature rise of 140 ° C every hour, for a little over an hour. At this point, the glass will start to lose its shape, especially in the middle. You can hold this temperature for 20 minutes if you want to get a flatter, wider bottle in the middle or go to the next step after several minutes if you want the middle to keep its shape.

Flatten Glass Bottles Step 13

Step 4. Heat quickly to 790 ° C

Heat the oven by increasing the temperature by 165 ° C every hour if you are using a ceramic mold or faster if you are not. Stay at this temperature until the bottles have lost their shape and assumed the desired shape.

  • This is the step that causes the most change depending on the type of bottle, ceramic oven and desired shape. Consider these numbers as starting points for your first project.
  • Always wear eye protection when looking through the peephole. If your oven does not have a peephole or window, you will not be able to check the condition of the bottles.
Flatten Glass Bottles Step 14

Step 5. Quickly cool the oven to around 540 ° C

Lift the ceramic oven lid, being careful to protect yourself from the heat that will emerge, to quickly cool the oven until it reaches a temperature between 480 and 590 ° C. The less time the bottle spends at a high temperature, the less you expose it to a risk of devitrification, that is to say to the formation of a cloudy haze in the glass.

Flatten Glass Bottles Step 15

Step 6. Anneal the glass

Glass undergoes significant stress when you heat it and can crack or become brittle if not "annealed," a process in which glass molecules are rearranged into a more stable pattern before cooling. There are two main ways to do this.

  • The simplest method, which is usually sufficient for most bottles, is to let the oven cool down gradually without lowering its temperature to less than 80 ° C per hour. If the oven cools faster, you need to restart it quickly to compensate for the cooling.
  • To anneal glass more efficiently, leave the oven at 480 ° C for one hour. Different types of glass also have different temperatures for annealing them, but to be on the safe side you should leave it between 540 and (or) 425 ° C for an hour, starting with the highest temperature.
Flatten Glass Bottles Step 16

Step 7. Let the oven cool to room temperature

The bottles should be completely flat. If you used ceramic kiln paper and there are any fibers stuck in the bottle, wear a mask while cleaning the glass.


  • If you've removed the label from the bottle and want to re-stick it, consider sticking it to the underside of the bottle to get a more aesthetic look and to avoid damaging it.
  • Take notes on the exact process you follow each time. Only your different experiences will help you find the best method for the oven and the bottles.
  • If you can't find a ceramic kiln, you can find one at a fine arts school. It is also possible to find it in art studios or other places where works of art are created with glass or ceramics.

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