Digitalfire Ceramic Glossary



•The secret to cool bodies and glazes is alot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com

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Ceramic Material


At first it might seem strange to define this, but it is not as obvious as it seems. In ceramics the concept of a material is different for different people. To a purchasing agent it is a commodity. To a geologist it is a mineral or mix of minerals. To a mining crew it is a stockpile of rocks or clay. To a processing department it presents a set of challenges to grind, separate, purify, size and package. To a production department it is a powder that makes up part of the recipe of a glaze or clay body. To a lab technician materials have a physical presence that can be tested and the results of these tests can be expressed on a data sheet. Labs can also deduce the chemistry of a material. But to a glaze chemist, a material is especially a warehouse of oxides. He/she assesses the physical and chemical contribution it makes to determine how to use it in a formulation. Recipes theoretically become 'material independent' (with limitations of course), the oxide needs can be supplied from whatever materials are at hand. The manufacturers of each name-brand material publish their chemistries.

Pictures

The recipe mixing area of Tony Hansen

Tony's lab work area of mineral and chemical powders for mixing test glazes and clay bodies. Stoneware and earthenware glazes are made from dozens (even hundreds) of commodity industrial mineral powders.

This is what a semi-trailer load (40,000 lbs) of talc looks like

Talc is not nearly as dense as many other materials. If this was silica these pallets would be half this height.

New Zealand Kaolin original container

The original bag of this product in 2014.

Ceramic materials can vary widely in density

A bag of magnesium carbonate beside a bag of feldspar. Although the former weighs 25 kg (vs. 22.7 kg for the feldspar), clearly it is a dramatically lighter (per volume unit) material. Lifting that bag of Mag Carb feels like lifting a pillow!

An example of a 50 lb bag of soda ash (or sodium carbonate).

Soda Ash is soluble and is thus not useful in most ceramic glazes. However that very solubility makes it very useful to control the electrolytics of ceramic slurries.

An original container of manganese dioxide

This bag will give you a clue as to what manganese dioxide is mainly used for.

Original container of Lithium Carbonate

An original container bag of Tricalcium Phosphate

A material storage rack

This material storage area employs a rack to keep pails off the floor so the area can be hosed down easily. The materials in each pail are sealed in plastic bags or the pail is covered with a lid.

Refined 200 mesh materials are not guaranteed to be such

Each of these eight pallets of kaolin are being sampled to screen them for oversize particles. The 50 gram samples needed can be taken without having to open the bags, they are filled through a valve at the top and it can be opened easily. Kaolins and ball clays especially are suspect and body manufacturers must be vigilant about this (each can tell you disaster stories about making product with faulty raw materials containing grit, carbon and iron particles). The samples will be washed through 70, 100 and 150 mesh screens to spot any particles that could introduce grit or fired speckle into the bodies.

Each 50 lb VeeGum bag is packaged in its own box

This is a quality but expensive material!

Raw red burning clay stockpile

The raw Plainsman M2 clay stockpile before it is ground. This is mined in Montana and imparts red color to various middle and low temperature clay bodies. It is a remarkably consistent material.

When both mineralogy and chemistry are shown on a data sheet

Some material data sheets show both the oxide and mineralogical analyses. Dolomite, for example, is composed of calcium carbonate and magnesium carbonate minerals, these can be separated mechanically. Although this material participates in the glaze melt to source the MgO and CaO (which are oxides), it's mineralogy (the calcium and magnesium carbonates) specifically accounts for the unique way it decomposes and melts.

Do not rely on material data sheets, do the testing

The cone 6 porcelain on the left uses Grolleg kaolin, the right uses Tile #6 kaolin. The Grolleg body needs 5-10% less feldspar to vitrify it to zero porosity. It thus contains more kaolin, yet it fires significantly whiter. Theoretically this seems simple. Tile #6 contains alot more iron than Grolleg. Wrong! According to the data sheets, Grolleg has the more iron of the two. Why does it always fire whiter? I actually do not know. But the point is, do not rely totally on numbers on data sheets, do the testing yourself.

Bulk 2500 lb bulk bags of Pioneer Kaolin

The material is much less dense than most other ceramic materials (that is why these bags are so tall). When moved the powder within becomes unstable and they are prone to falling over.

What can you do using glaze chemistry?

There is a direct relationship between the way ceramic glazes fire and their chemistry. Wrapping your mind around that and overcome your aversion to chemistry is a key to getting control of your glazes. You can fix problems like crazing, blistering, pinholing, settling, gelling, clouding, leaching, crawling, marking, scratching, powdering. Substitute frits or incorporate better, cheaper materials, replace no-longer-available ones (all while maintaining the same chemistry). Adjust melting temperature, gloss, surface character, color. Identify weaknesses in glazes to avoid problems. Create and optimize base glazes to work with difficult colors or stains and for special effects dependent on opacification, crystallization or variegation. Create glazes from scratch and use your own native materials in the highest possible percentage.

Out Bound Links

In Bound Links

  • (Project) Ceramic Materials Overview

    The study of ceramic materials is at the center of...


By Tony Hansen




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