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The Majolica Earthenware Process

Section: Glazes, Subsection: Low Fire

Description

Understanding the advantages and disadvantages of low fire ware and the chemistry of physics of the glazes and bodies used is a key factor to exploiting this type of ceramics

Article Text

Majolica (or tin glazed earthenware) is a very old pottery process that has long fascinated collectors. The term 'majolica' is Italian (from the port of Majorca), however, the technique was also perfected by the Spanish, French, Dutch, and Slovaks. It is characterized by white-glazed red earthen-ware clay decorated with over-glaze floral and other brush work designs.

Advances in ceramic materials, kilns, and stain technology make it possible or you to produce attractive and exciting majolica-like ware today that is technically superior to any of the classic ware of the past. Although the formidable challenges took hundreds of years to overcome, with a methodical approach now you can have majolica working in weeks! However, some aspects of earthenware are much more difficult to perfect than with stoneware. Glaze manufacturers in the ceramic hobby market have shielded users from this complexity, but at a cost.

Forgive me, however, for not holding true to the traditional materials. In this sense, I use the term 'majolica' loosely. For example, there is no compelling reason to use tin to opacify the glaze and lead flux is no longer needed or even legal. It is reasonable to fire a little higher and longer for better ware strength, and introduce new decoration materials and techniques. In fact, it is not even necessary to use a white glaze with overglaze stains if white and colored slips can be covered with a transparent glaze.

If you have studied or seen majolica ware, you may have dismissed it for a number of reasons. But are they valid? You might say:

Majolica's Advantages

A few things to be aware of:

Getting Started With Your Own Majolica

Repeat the above process until the glaze fits well. You now have a reliable transparent glaze.

Add 12% zircon opacifier (i.e. Zircopax or Superpax) and mix the glaze and try it again on a tile. If the color is not white enough, increase the opacifier to 15% or more, but be careful since zircon increases glaze melt viscosity, and thus, raises the likelihood of crawling and pinholing.

When the desired opacity is achieved, stress test, as above, to reveal possible shivering. This needs to be done because zircon will lower the expansion considerably. If the problem appears, replace part of the frit content with a higher expansion frit and redo the test. Repeat the process until the fit is good. You now have a reliable white glaze.

You now have the over and underglaze colors ready.

Apply the slip in a thick layer to a leather hard tile. Dry the tile. If the slip shrinks and cracks into flakes with curled up edges, remove the bentonite and retest. If it still does it, add kaolin at the expense of ball clay. If the slip flakes and falls off during drying, add ball clay at the expense of kaolin (10% to start).

You now have a working slip base. The final step is to develop some colored slips.

Now you have everything ready and you know it works. You are in control. I suggest you glue all successful glaze and slip samples on boards and hang them up in plain view as inspiration and direction.

To begin production, I recommend you get a 50 lb. bag of frit (about $100) and mix 5-10 gallons of white and transparent glaze. It is always better to dip the ware completely to get an even layer. If you don't have a pair of dipping tongs, be sure to get some.

Armed with the above working materials, spend the rest of your life investigating the infinite number of combinations, colors, and decorative techniques possible. Enjoy.

Which is stronger: Cone 10R mug or cone 03 mug?

Which is stronger: Cone 10R mug or cone 03 mug?

The mug on the left is high temperature Plainsman P700 (Grolleg porcelain). The other is Plainsman Zero3 fired at cone 03. Zero3 has a secret: Added frit which reduces the porosity of the terra cotta base (therefore increasing the density) dramatically. How? The frit melts easily at cone 03 and fills the interparticle space with glass, that glass bonds everything together securely as the piece cools. Although I do not have strength testing equipment right now, I would say that although the P700 mug likely has a harder surface, the Zero3 one is less brittle and more difficult to break.

Low fire nirvana: Use commercial underglazes but make your own clear over glaze

Low fire nirvana: Use commercial underglazes but make your own clear over glaze

Decorate ware with the underglazes at the leather hard stage, dry and bisque fire it and then dip-glaze in a transparent that you make yourself (and thus control). These mugs are fired at cone 03. All have the same transparent glaze (G2931K), all were decorated with the same underglazes. Notice how bright the colors are compared to middle or high temperature. On the left is a porous talc/stoneware blend (Plainsman L212), rear is a fritted Zero3 stoneware and right is Zero3 fritted porcelain. When mixed properly you can dip ware in this glaze and it covers evenly, does not drip and dries enough to handle in seconds! Follow the Zero3 firing schedule and you will have ware of amazing quality.

G2931K Zero3 transparent glaze on Zero3 Fritware Porcelain

G2931K Zero3 transparent glaze on Zero3 Fritware Porcelain

This is an all-fritted version of G2931F Zero3 transparent glaze. I formulated this glaze by calculating what mix of frits must be employed to supply the same chemistry of the G2931F recipe. The mug is made from the Zero3 porcelain body (fired at cone 03) with this glaze. This glaze fits both the porcelain and the Zero3 terra cotta stoneware. The clarity, gloss, fit and durability of this glaze are outstanding.

Three low fire bodies need three different clear glazes. Why?

Three low fire bodies need three different clear glazes. Why?

Glaze fit. The left-most clay mug contains no talc (Plainsman Buffstone), the centre one about 25% talc (L212) and the right one is about 45% talc (L213). Talc raises thermal expansion. The centre glaze is G2931K, it is middle-of-the-road thermal expansion (Insight-live reports it as 7.4) and fits the low-talc bodies (and Zero3 porcelain and stoneware). But it crazes on Buffstone and shivers on L213. The lesson is: Forget about expecting one clear or base glaze to fit all low fire bodies. But there is a solution. I adjusted it to reduce its expansion to work on zero-talc porous bodies and raise it to work on high talc bodies. How? By decreasing and increasing the KNaO (in relation to other fluxes). The three fire crystal clear and work the best in a drop-and-hold firing.

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By Tony Hansen




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