Because there are variables beyond my control (clays, papers, water, mixing errors and etc) always pre test fire what you have before a big project. No guarantee can be offered that 'alternative" commercial paperclays now on the market will meet the all the performance advantages of my high performance trademark P'Clay® brand only available from licensed manufacturers/distributors.
"P'Clay® / P'Slip® product line of ceramic paperclay specific paper (cellulose fiber) ingredients have been tested and certified safe and non toxic for art clay use."
quote from the Duke University lab report. Duke University lab certified ingredients meet or exceed ACMI non toxic art material standards.
ceramic paperclay and paperslip safety certification and info links
Unlike traditional ceramic clay which is usually aged, P'Clays®P'Slip® should be used AS SOON AS POSSIBLE after purchase. P'Clay® should arrive with a normal appearance. When not "fresh" and if stored in some hot and humid climates "over time" in some, but not all, base clays there is a chance of mold growth. Usually this shows as dark streaks similar to mildew on the sides of the moist block that can be scraped off the surface with a rib or blade, and the interior is still fine.
If within a week of purchase your P'Clay shows signs of "age", you should get a discount on it's price, or have it exchanged for some fresher batch. When P'Clays "dry out" the conditions for mold growth are less favorable and most stop completely. A kiln fire further destroys and burns up residual traces of mose microbial growth.
Bleach is never used in a recipe for any trademarked product and is discouraged in any form. Preservatives may have been added to some clay bodies to extend shelf life. Shelf life of moist paperclay varies from months to years depending on clays used and temperatures of storage. Microbes will grow faster on the terra cotta blends and slower on most porcelain blends.
As with all art materials, those with skin allergies may want to wear gloves and test a small sample first.
Use at your own risk as there are too many variables of individual users, climate and storage conditions to offer a 100% guarantee here.
You may insist on only the freshest possible batch used within weeks or months of purchase to reduce risk further. Particularly so if working with children.