You are here:

Pottery/Process for Slumping Glass Bottles


I would like to start melting glass bottles. What size cone do I need to use for that? Can I use silica sand and lay the bottles right on the sand instead of using kiln paper? Kiln paper is so expensive, I'm just starting out. Also, can I use a regular ceramic mold to slump the bottles? Will kiln wash work as well?

Thank you very much for your time,
Sharon Whitt

Dear Sharon,

Thank you for your recent question. Slumping glass bottles is a fairly easy process and can be done with few and simple tools.

Yes, you can use silica sand or kiln wash to slump your bottles, however, you will only have a flat bottle at the end of the process. To create a bottle with a concave indention you will need a mold. You can purchase slump molds online by typing "glass slump mold" in your search engine. Depending on the size and shape, they run between $10 and $50, but because they are reusable, you can purchase them when you can afford them.

When slumping bottles, it is unnecessary to use cones as you will be altering your kiln temperature by ramping (increasing) or flashing (decreasing) your temperature throughout the slumping process. Therefore, a pyrometer with a thermocouple is used to gauge the temperature as you ramp or flash the kiln. These two tools can be purchased for under $100 dollars. I suggest getting a digital pyrometer for accuracy in reading temperatures. I suggest a 12" thermocouple Type K with a block as it has a longer wand so when you insert it into the kiln, you don't experience too much heat. Always wear gloves when using the thermocouple to prevent burns.

The site shows some examples of pyrometers and thermocouples.

The process for slumping bottles is below. I have also included a recipe for the De-Vitrification Solution so you don't have to buy it.


Glass Bottles
Kiln Wash
Bottle Mold (if desired)
De-Vitrification Solution (See Recipe Below)
Dish Washing Liquid
Pyrometer with Thermocouple
Kiln poker or metal rod
Kiln gloves or heavy grilling mits


1. Empty and wash the glass bottle with dish washing liquid. Be sure and remove any paper, metal rings or plastic from the bottle. Rinse the bottle well and allow to air dry.

2. Vitrification occurs when a bottle is colored or cools too quickly. It creates a matte finish on the bottle's surface. Although it can be created as a decorative surface, most glass artist's find it unappealing and choose to devitrify their glass with a solution, prior to firing, to assure this effect does not occur. Should a bottle vitrify, the bottle can be re-fired after several coats of De-Vitrification Solution is applied.

  Apply De-Vitrification Solution by spraying onto the bottle. Let dry completely between coats. Apply 3 coats. (See De-Vitrification Solution below)

3. Prepare the kiln shelf by applying kiln wash to the surface of the shelf. Three coats must be applied in a crisscross manner to assure the shelf is covered completely. Let each coat dry for 2 minutes before applying the next coat.

4. Carefully lay the bottle in the center of the kiln on the prepared kiln shelf.

5. Start your kiln with the peep holes open and the lid cracked to 2 inches. Turn on the lower element and let the kiln begin to warm for 2 hours.

6. Increase the kiln temperature by 250 degrees F for 1 hour.

7. Increase the kiln temperature by 250 degrees F for 1 hour.

8. Increase the kiln temperature by 250 degrees F for 1 hour.

9. Close the lid and plug both of the peep holes after the hour in # 8 and increase the kiln temperature by 100 F degrees.

10. After you have ramped the kiln in # 9, turn on the pyrometer and insert the thermocouple into the lower peep hole of the kiln, or a special thermocouple hole already drilled into the kiln. Check the temperature. Depending on your kiln, the temperature should be around 1000 degrees F. Since you are increasing the kiln another 100 degrees F, you will need to watch the kiln carefully until it reaches 1100 degrees F. Check the kiln every 10 minutes using the thermocouple until the kiln reaches 1100 degrees F.

11. When the kiln reaches 1100 degrees F, soak the glass bottle by keeping the kiln at 1100 degrees F for 10 minutes. Do this by keeping the thermocouple inside the kiln hole and watching the temperature. If it tries to go beyond 1100 degrees F, using gloves or a kiln poker, crack the lid to bring down the temperature to 1100 degrees F. If the kiln begins to cool below 1100 degrees F, close the lid. Maintain this balance until the kiln has soaked at 1100 degrees F for 10 minutes.

12. Close the lid, if opened, and remove the thermocouple. Increase or ramp the kiln 250 degrees F for 1 hour.

13. Increase the kiln to 1425 degrees F at any ramp speed you choose. Your bottle is in no danger of cracking at this stage.

14. Check the temperature of the kiln to assure you have reached 1425 degrees F. Once you reach 1425 degrees F you will want to flash or decrease your kiln quickly to 1100 degrees F. To do this, open the lid using gloves and the kiln poker. Use the thermocouple to gauge your temperature. This will prevent the vitrification of your bottle.

15. Once the kiln reaches 1100 degrees, the vitrification process is over. Lower the lid and turn off all switches to cool the kiln naturally. This is the annealing process. To prevent shattering the bottle, do not open the kiln during the cooling process. Allow the bottle to cool naturally until the kiln can be opened with your hands and the bottle removed without gloves.

De-vitrification Solution:

Follow the instructions below carefully to prevent spotting on your glass bottles


4 cups distilled water
1/4 cup 20 Mule Team Borax
2 Tablespoons Bullseye Glastac. You can try clear nail polish as I have used because it is much cheaper.
2 clean, 1 quart plastic containers with lids. I like to use empty milk containers.
coffee filter
rubber band


Mix all ingredients very well in one container by shaking for approximately 5 minutes.

Allow mixture to sit, undisturbed, overnight.

Insert the coffee filter into the mouth of the second container and until a pocket is formed inside the container. Using the rubber band, place it around the mouth of the container, over the filter to prevent the filter from slipping into the container.

Carefully pour the contents of the first container into the second, trying not to pour the settled borax into the filter. The purpose is to only retain the liquid from the mixture.

Discard the contents of the first container.

The liquid contents can be brushed onto the glass bottle before firing to prevent vitrification. Be sure and close the lid on the container tightly to reserve the liquid for future use.

I believe I have covered the steps in slumping glass bottles. If you have further questions, please feel free to contact me at any time. I am always at your service. Good luck on your future venture!

Ms. Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat


All Answers

Answers by Expert:

Ask Experts


Ti Phillips


Will answer any questions on hand building, wheel, glaze, firing. Speciality questions to include those in glaze calculation and development, firing techniques. Please do not send questions on identifying pottery. Although I would love to add this to my question topics, I have a retreat to run as well as the studio and volunteering on AllExperts, and therefore do not have the available time to research indentification and marks. Thank you for understanding.


Experience includes 30 years in pottery design and education. Have taught online and studio classes worldwide for the last 20 years. Own a pottery retreat specializing in firing techniques. Have 12 years solid experience in glaze calculation and formulation as well as problem solving in glaze chemistry. I am the first potter in the United States to have developed a complete package of pottery equipment blueprints for a studio. The blueprints include wheels, kilns, studio furniture, wedgeboards, raku kilns, slab rollers, ball mills and studio tools.

Alliance of Pottery Artists Worldwide Association

Ceramic Industry - PPP Wyndstryder Press - Pottery Journal

University of Sciences and Art's of Oklahoma, studied under Professor Jaymes Dudding.

Awards and Honors
Potter of the year with APAWA, various awards for showmanship and design.

Past/Present Clients
Available upon request.

©2016 All rights reserved.