Post #380649 by Babalu on Thu, May 15, 2008 11:18 PM

Sorry Mad Dog, I didn't see your question before. Your cone 5 slip will shrink more than the lower fired slip, but it will also tend to be a stronger mug than the low fire ones will be. There is not a ton that is different, cone 5 clay will be more vertrifyed and will not be able to handle all the different colors that a lower fired clay will. Below is a discription of clay bodies that I pulled from an old Clay 101 class I had on file...kind of long...but hey, I guess I will see you at my studio sometime this weekend.

Clay is a compound of minerals and organic material resulting from the natural decomposition of certain igneous rocks (for example, feldspar and granite are two common sources of clay minerals). As these mineral deposits age and get moved around by natural forces (wind, water, glaciers), chemical changes occur which cause the materials to become clay. The two major classes of naturally occurring clay deposits are primary clays and secondary clays. Primary clays are those that remain at the physical location where the parent rock decomposed. These clays tend to be the most pure, but tend to be less plastic than secondary clays. Secondary clays are deposits that have been transported by wind, water, or glacial activity. These clays, while still very pure, generally have had other materials introduced into their basic composition that change their performance characteristics (color, plasticity, etc.)

Types of Clay

Clays can be grouped or classified several ways: according to the way they are found in nature, by their physical and chemical properties, by the way they are used tomake finished properties, and so on. One of the first ways to classify clay is by the methods used by Mother Nature to create clay deposits. The major types of naturally occurring clay are as follows:

Kaolin or China Clay

Chemically known as Al2O3-2SiO2-2H2O this clay is almost pure white as a primary clay and slightly less white but more plastic as a secondary clay. These clays are a major component of most high-fire porcelain clay bodies and are frequently used in stoneware to lighten the fired color.

Ball Clay

These are secondary clays that have been transported to swampy areas where organic acids have broken down the mineral particles to ultra fine size. These clays are extremely plastic – if used alone they will shrink quite a bit, causing severe cracking.

Earthenware Clay

Earthenware is the most common surface clay found throughout the world. These clays usually contain high amounts of iron, which gives the fired wares the characteristic terra cotta color. True earthenware clay cannot vitrify, which means the clay body remains porous after firing.

Stoneware Clay

Stoneware tends to be kaolins that contain more impurities - usually calcium, feldspar, and iron - resulting in clays that have finer particle sizes and higher flux content. The flux materials cause the clay to vitrify at lower firing temperatures.

Fire Clay

Similar to stoneware clays, fire clays generally contain less flux (especially calcium and feldspar). Fired alone these clays won’t fully vitrify – even at high fire temperatures.

Bentonite Clay

Bentonite is formed from the decomposition of volcanic ash. Bentonite has the finest particle size of any natural clay. It is very useful as a plasticizer but it must be used in moderation – too much of it in a clay body will result in cracking during the drying process.

Slip Clay

These are naturally occurring clays that have a high iron content. At high temperatures these clays melt to form a glaze; no additives needed. Pure natural clays almost always have shortcomings – in a potter’s eyes. The production processes and ultimate use of the piece dictates the properties the clay needs to have – either during the forming stage or as a finished piece. Aclay body is a mixture of clay and other materials designed to meet the needs of the user. Design objectives for a clay body may involve making it more plastic during the throwing stage, improving the body’s stability in large-scale work, helping the body resist thermal shock from firing, and improving general properties such as vitrification and density. The “other materials” in a clay body perform a specific function to make the final product work better for the clay user. Ageneral description of each component and its purpose are discussed below.

Components of a Clay Body

All clay bodies involve combining clay (many recipes call for several types of clay) with non-clay additives. The basic types of additives and the purpose for each are as follows:

Flux

These materials act as melting agents, helping to lower the maturing temperature and assist in the formation of glass - the essential binder in all ceramics. Some clay contains higher concentrations of fluxes naturally–feldspar and iron are the most common.

Glass-Formers

These materials react with fluxes to form glass. The most common glass-former is silica. Pure silica melts at very high temperatures – the proper mix of flux materials and silica allows for glass to be formed at more manageable temperatures. This balance must be carefully achieved – too much flux produces a weak glass, too much silica can lead to reduced thermal shock resistance.

Refractories

These materials stabilize the body, providing the physical

Hope you can make since of all this...