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The Majolica Earthenware Process

Section: Glazes, Subsection: Low Fire

Description

How to make strong, durable functional ware from red terra cotta odies based on the traditional of majolica.

Article Text

Traditionally, “Majolica” is white-glazed red earthenware clay decorated with over-glaze brush work designs. But I am guessing you are not at this page for a history lesson. You want to make ware that looks like Majolica. Even durable functional ware. Although the formidable challenges took hundreds of years to overcome, with a methodical approach you can have the process working relatively quickly! Notwithstanding that, some aspects of earthenware are more difficult to perfect than with stoneware.

I am also guessing that you are open to improving the process and ware quality by taking advantage or modern materials and equipment. Today, there is no compelling reason to use tin to opacify your glazes, zircon is less expensive. You can even dispense with the white glaze and use a white engobe with a transparent overglaze. And certainly not a lead flux to melt glazes. It is also reasonable to fire a little higher for better ware strength (a lot better). Or even flux the body to get better strength. And why not introduce new decoration materials and techniques we have now?

Common Misconceptions About Low Fire

Majolica Characteristics We Could Leave Behind

Low Fire Advantages

Majolica is techically terra cotta with a white glaze. What are some advantages of terra cotta (especially at a higher-than-normal temperature)?

A few things to be aware of:

Getting Started

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.

Test bars of different terra cotta clays fired at different temperatures

Test bars of different terra cotta clays fired at different temperatures

Bottom: cone 2, next up: cone 02, next up: cone 04. You can see varying levels of maturity (or vitrification). It is common for terra cotta clays to fire like this, from a light red at cone 06 and then darkening progressively as the temperature rises. Typical materials develop deep red color around cone 02 and then turn brown and begin to expand as the temperature continues to rise past that (the bottom bar appears stable but it has expanded alot, this is a precursor to looming rapid melting). The top disk is a cone 10R clay. It shares an attribute with the cone 02 terra cotta. Its variegated brown and red coloration actually depends on it not being mature, having a 4-5% porosity. If it were fired higher it would turn solid chocolate brown like the over-fired terra cotta at the bottom.

Soluble salts on cone 04 terra cotta clay bodies

Soluble salts on cone 04 terra cotta clay bodies

Low temperature clays are far more likely to have this issue. And if present, it is more likely to be unsightly. The salt-free specimens have 0.35% added barium carbonate.

Stoneware from your terra cotta body? Is is very possible.

Stoneware from your terra cotta body? Is is very possible.

Some terra cotta clays can be used to produce stoneware by firing them a few cones higher. Terra Cottas are almost always nowhere near vitrified at their traditional cone 04-06 temperatures, so they can often stand much higher firing. However, clear glazes do not usually work well in higher firing since products of decomposition from the vitrifying body fill them will micro bubbles, clouding the surface. In addition, the body turns dark brown under clear glazes. But with a white glaze, these are not a problem. This is Plainsman L210 fired to cone 2. The glaze is 80% Frit 3195, 20% kaolin and 10-12% zircopax, it fires to a brilliant flawless surface.

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By Tony Hansen




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