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A Bit About Shivering: Article or Project

Glazes that peel off of ceramic or clay bodies after firing. This is not to be confused with crazing or crawling which are entirely different issues.

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Shivering is a failure that happens with glazes during the firing process. It has long been credited to an incompatibility with glaze and greenware. Essentially, it is when the glaze does not 'fit' the clay body when cooled. There are many kinds of clay and slip available, many recipes. There are also many glazes on the market produced by a number of companies. When the wrong glaze meets up with the wrong clay body, the result can be ‘shivering’.

The term shivering is often confused with the terms crawling and crazing, but they are different issues. The common factor is an incompatibility between glaze and clay; however, shivering is when the fired glaze cracks and curls up or pops off the bisque-ware. The edges are sharp and the glaze continues to break away well after the piece has cooled. The item can only rarely be salvaged and because of the danger (cuts), it is best to dispose of it or put it on display and an example of ‘failed’. Glaze can pop of immediately when cooled or over a period of time, even years later.

If you have a glaze the 'lifts' off several clay pieces, then the issue is most likely the glaze formula. If you have different glazes on the same clay body and several 'lift', then the issue is probably the clay.

It has been interesting reading online posts from folks who have never experienced it before and how one thing in the kiln may fail and others not. It has been happening quite frequently of late which led my mind to wonder…. ‘why?’ There has been a noticeable increase of the occurrence with slipcast ware. The clay companies say, ‘Not our fault’ and same goes for the glaze companies. My analytical mind would not rest and then a possible answer struck me.

There have been so many changes in the industry both with glazes and clays. Closure of a major Talc mine, created a scramble with the clay/slip companies to reformulate their recipes. Involvement with the EPA in the 90’s required changes in both the clay and primarily with the glaze and paint formulas. The companies have worked hard to develop safe products that give optimum results. So why is the problem becoming more prevalent?

So here is my ‘theory’ for what it is worth. If the new slips are compatible with the new clays and there is still a problem of shivering, what could it be? My conclusion is that a lot of ceramists are using the old formula glazes and/or the old formula underglazes in their finishing techniques. But wait, there is more.

Many of the old formula of underglazes are primarily made with a ‘clay’ base. Aha!

So, here we have….

a new recipe of clay with an old recipe glaze… possible shivering

a new recipe of clay with an old recipe (clay base) underglaze and a new recipe glaze... possible shivering

a new recipe of clay with an old recipe (clay base) underglaze and an old recipe glaze… slight possibility of shivering, but less likely.

So, does this mean ceramists should no longer use the old paints and glazes? By no means quit using them, but consider doing some test samples … specifically old glaze on new clay and new glaze on old underglaze.

Remember, this is just a theory built from 60 years of working ceramics/clay arts. I welcome differing views. Please send us your thoughts.

** Note: photo credit to unknown source.

 

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