Most ceramics suppliers carry a line of clays, ranging from low-temperature, white casting slips to dark stoneware for throwing on the wheel. Specialized blends of clay are frequently available for salt/soda firing, Raku, mid-range porcelain, and slip casting. The appropriate choice for moist premixed clay depends on several factors that are distinctive to each potter: forming method, firing temperature range, kiln atmosphere, glaze, and fired color. Ceramics suppliers usually have several different premixed clays within a given range.
Before you choose a supplier, ask other potters for their recommendations. For example, choosing a supplier that sells low-priced clay but doesn’t have a good reputation ultimately can be very expensive, due to improperly mixed clay, random delivery schedules, lack of technical support, and substandard business practices. The price of a stock moist clay or private formula clay is really not relevant; the rate of defects produced by a given batch of clay is. (Ceramics suppliers for the most part do not keep these types of records, or if they do, they don’t tell this to customers. However, other potters can relay their experience with a particular clay, helping you choose a clay body with a good result for others.)
Establishing a good professional relationship with your supplier has several benefits. The ceramics supply company’s sales and technical staff can be an added help in obtaining information about premixed clays. They can offer advice on how other potters are using the clay and supply information on dry clays that are available for use in private clay body formulas.
Another thing to keep in mind when buying premixed clay is that your shipping costs will be lower from a supplier that is nearby. But keep in mind, the overriding consideration when choosing a ceramics supplier is not the cost or delivery charge, but the quality of the clay. Any small savings in choosing a clay just for its low price can be a negated if the clay formula is not sound or the mixing procedures inaccurate.
ORDERING MOIST CLAY
If you choose a local clay supplier, visit the clay mixing operation. This is a valuable opportunity to determine how seriously a ceramics supplier regards the clay mixing part of the business. Simple observations lend significant clues. Arc the clay storage and mixing areas reasonably clean and well organized? Do the people mixing clay appear motivated and knowledgeable? Are any special cleaning procedures enacted when mixing white clays or porcelain? (They are easily contaminated with non-white firing clays.) What quality control measures are taken when different clay body recipes are mixed?
ORDER EARLY AND OFTEN
Always reorder moist clay when only half of your current supply is exhausted. This will allow an opportunity to randomly rest fire the new clay while you are still using a proven batch of old clay.
Also, keep careful records for each batch of day, noting the production code on each box. A shipment containing several batches may have more chan one production code. Most suppliers package moist clay in 50-pound (22.7-kg) boxes char contain two 25-pound (11-kg) bags of clay. The clay is packed in plastic bags , which are semi-permeable,
and air will begin to harden the clay within a few months. Check the moisture content of clay in plastic bags pc.riodi cally co ensure ir has nor hardened. If it has, spray some water on the clay and reseal the plastic bags. You might have to repeat chis procedure several rimes co achieve a higher moisture content in the clay and a softer clay.
REPORT PROBLEMS IMMEDIATELY
If you have problems with the premixed clay, report them immediately to the supplier, listing the production code and a description of the fault, and be prepared to send a sample of the defect for evaluation. Do not continue to use a clay-or any product for that matter-once you have encountered a problem, because this can constitute acceptance.
As a standard business policy, ceramics suppliers have limited ability on dry and moist clay, which means, at best, they will only replace: the product if it is defective. Suppliers will not replace: kilns, shelves, or posts damaged by defective clay. Nor will they compensate you for lost time or potential sales caused by defective clay.
Keep in mind that suppliers will replace clay only if it can be proven the clay was at fault and you did not cause the defect through improper forming, glazing, or firing. So for example, if you mistakenly fire a cone 06 (1828°F
PRIVATE CLAY FORMULAS
When you buy premixed clay, you might discover that no ceramics suppliers’ stock clay bodies meet your specific needs. Perhaps you need a private clay formula, a formula designed just for you. Some suppliers offer this added service. You find or create a clay body formula, which the ceramics supplier will then mix.
Bear in mind that when a supplier mixes a private formula, the supplier docs not assume any responsibility for potential defects caused by the formula. You must fell confident that the private formula clay will work in the following respects: forming method, kiln atmosphere, glaze interaction, temperature range, and fired color.