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When we talk about clay, there are thousands of clay vessels available for purchase. But there are 3 main types of clay commercially used for pottery. These are earthenware, stoneware, and porcelain. Primary clay is the purest form of clay, but most manufacturers do not prefer it because it is harder to work with or they may choose to use many additives to improve its performance. Keep reading to learn more about these types and which one is best for making clay pots.

Earthenware:

It is also called terracotta and is a combination of low fire natural clay and many additives. The potters either harvest it from the ground or buy commercially processed clay. It is not the purest form of clay and is called secondary clay.

The firing temperature ranges between 1479 and 2109 d F. It looks red or orange because of high content of iron oxide, which is essentially rust. Some makers use other additives to make it yellow, white, tan or buff.

The makers often add frit (glass powder) that melts during firing and increases its density, making it stronger and less porous. If no frit is used, the pot turns out so porous that it cannot hold liquids, so it is glaze fired. This means the makers paint, dip, or spray raw glaze (made from metal oxides and/or chemicals) onto the pot and fire it again. The glaze melts and hardens forming a glassy and shiny layer over the pot. This process makes it waterproof.

The excessive use of additives and glazes makes earthenware pots toxic. They leach and contaminate food while cooking.

Stoneware:

It is an umbrella term that refers to a variety of different clay bodies – all using secondary clay. In general, stoneware is tough when fired, is denser, more resistant to breaks and chips and is less porous. They are fired at higher temperatures – somewhere between 2010-2370 d F.

It comes in deep shades of grey and lightens up when fired as it loses all the moisture. It has a speckled look because of all the impurities. Broadly speaking, it is a mixture of feldspar, quartz, and ball clay.

The makers also add fired and ground up clay granules, called grog, to make it easier to work with and resistant to cracks. Feldspar reduces the melting point of glass forming impurities in stoneware. As a result, it produces more glass during firing that takes away the porosity and makes the pot waterproof.

These impurities and additives leach dangerous toxins into food that, eventually, can cause serious health problems.

Porcelain:

Sometimes also referred to as kaolin clay, porcelain is a more refined variety of clay. Kaolin is a white clay also known as China clay. It is high fire clay, and the firing temperatures are often above 2300 d F.

Once fired, the off-white color changes into a translucent appearance. The fine particles in porcelain are higher than that is earthenware and stoneware. This makes it non-porous, impermeable, and very dense. The makers often mix feldspar, quartz and ball clay into the porcelain.

It has a reputation of drying up too quickly and being challenging to work with. The makers need to use many chemical additives to slow down the drying and control its plasticity. These additives and the impurities in this clay make the final product toxic to food.

Two other varieties of clay – Ball clay and Fire clay are sold in powdered form. But they are only used as additives while making pots from the main varieties. They control shrinkage, resistance to cracks, plasticity, and heat resistance. Both are made from secondary clay mixed with reactive additives like kaolinite, alumina, silica and iron impurities. Using these as additives in the raw material makes the pot toxic.

Primary Clay: Why MEC makes cookware from only primary clay

As mentioned in the beginning of this article, most manufacturers prefer not to use primary clay. But this is the only variety that is free from impurities and can potentially make a 100% non-toxic cookware. Is it possible to make primary clay pots without toxic additives or glazes? The answer is yes.

Miriams Earthen Cookware (MEC) is a US-based company that makes pots and pans from lab tested primary clay. The manufacturing process demands a lot of effort and caution but is totally worth it. This ‘labor of love’, as the makers like to call it, yields the healthiest cooking pots that cook food without contaminating it and while preserving all the nutrients.

MEC individually handcrafts each piece and uses no additives or glazes, so the pot turns out as pure and non-toxic as the raw material. The pots are versatile and full of healthy features (read more about them here) which enables them to cook healthy and nutritious food. Sign up for MEC newsletter to get notice of cooking classes, recipes and other helpful MEC cooking tips (at the bottom of the page here).

Interested in cooking your next meal in MEC’s healthy clay pots? Head over to our online store and order a pure clay pot today.