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Pottery/Using Glass as a Glaze

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Question
Hello,
Let me preface this by telling you that my kiln is a Home Artist kiln that fires to 05/06. I like to try and make things that are food safe but still cool looking. I'm working on some sea life related plates and I'm struggling to find some cool glazes that are food safe in my cone range. I love using glass and was wondering if it is a good medium to use for that, either by itself or if I put clear glaze on that?  I know that glass will crackle, so I thought if I put clear glaze over it to seal it. I realize I have some some restrictions because of my low firing abilities... If it's not possible with my current situation, is it possible if I had a high firing kiln (for future reference)?
Thank you!

Answer
Dear Regina,

Thank you for your recent question. The use of glass as a glaze requires more than just placing glass on a clay body. It can be done, but the firing process is much different than firing with glazes to prevent shattering of the glass and crackling. Second, although the glass may have a color to it, the color in most cases will burn off or pool, creating a large area of clear glass and a small area of pooled color. The only exception to this rule is when using old cobalt glass, which is often rare to find and very expensive.

I am not sure why you are having problems finding low fire glazes that are suitable for functional ware such as ware that is food safe. Most low fire glazes are food safe, with the exception of glazes that have crystalline effects, foaming or metallic glazes. General color glazes are almost always food safe.

Just because your kiln only fires to 05/06, doesn't mean you are not reaching temperatures that are food safe. Food safe firing needs two properties. One, to adhere and fuse to the clay body in a complete uniformed flow and two, not contain raw materials that may leach into food products, i.e., lead. Leaching is most important when working with low fire glazes because raw materials such as lead does not burn off in low fire glazes. Therefore, you do not want to purchase glazes that have lead or barium in them. Thus, these glazes will state they are not food safe.

I have listed some links to websites where you can look at the types of glazes that would be suitable for your functional ware and your kiln firing temperature needs. Take a look at these glazes and see if these would be suitable for your work.

Furthermore, if you wish to use glass in your glaze work, success has often been achieved by placing shards of glass on the surface of the ware after glazing, letting it melt with the glaze. The glaze helps the glass adhere to the surface and flow with the glaze during the melting process. Sometimes you can get really great effects from this. However, using too much glass can cause a thick pooling of it in low areas, such as the bottom of a bowl or cup, so be careful as to how much you use. I would say a couple of small pieces about 1" each for a bowl or cup and maybe 3 or 4 1" pieces for saucers and plates. You do not need to seal the surface with clear glaze is you allow the kiln to fire to maximum cone of 05.

Below are the websites for the Cone 05 glazes.

Gloss Glazes

http://www.amaco.com/t/glazes-and-underglazes/low-fire/low-fire-gloss

http://www.amaco.com/t/glazes-and-underglazes/low-fire

Matt Glazes

http://www.dickblick.com/products/amaco-lead-free-matt-glazes/

Remember to read through each to make sure they are food safe. Most of these are.

I hope this helps you. If you have further questions, please feel free to contact me again at any time. I am always at your service. Please be sure and rate my service to you. Thank you kindly.

Sincerely,
Ms. Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat
www.earthstokenfire.com

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Ti Phillips

Expertise

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

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.

Organizations
Alliance of Pottery Artists Worldwide Association

Publications
Ceramic Industry - PPP Wyndstryder Press - Pottery Journal

Education/Credentials
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.

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