Nowadays, a lot of cookware is advertised as “ceramics”. Moreover, we became surrounded by the tone of misleading claims about ceramic cookware. Starting from statements about the quality and performance down to the safety “facts”.
From my beginnings of learning about cookware safety(see more on About me page), one of the biggest confusions that I had was understanding what are different types of cookware advertised under the name “ceramic”. I spent some time understanding the ceramic production technologies, and contacting the people with expertise to make it more clear.
In this article, I will go deeper into what ceramic actually is and make it easier to understand are utensils advertised under “ceramics” actually made from this material.
In general, most of the cookware called ceramics is not made from this material. There are two main categories of cookware marked as ceramics, pure ceramic cookware, and ceramic coated cookware. Unlike the first one, the ceramic-coated cookware is not made from ceramic material but it only has a ceramic-like appearance.
In this article, I will dig deeper into the topic of both ceramic-coated and pure ceramic cookware, ways to differentiate them on the market, and the exact materials that they are made from. Moreover, I will provide you with references to my other articles about the healthy aspects of mentioned cookware types as well as their performance.
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Is ceramic cookware really ceramic?
Two types of ceramic cookware exist on the market including ceramic coated cookware also known as non-stick ceramic cookware and pure ceramic cookware also known as pottery.
Unlike pure ceramic cookware(pottery) ceramic-coated cookware is not really made from ceramics and I will go deeper about it in this second subheading.
Ceramics is material made from thermally processed clay, and this is what pure clay cookware is made of.
Clay is a soil material made from very fine-grained minerals called hydrous aluminum phyllosilicates, or clay minerals. Those minerals mainly consist of alumina(aluminum oxide), silica(silicon dioxide), and some other elements that depend on the type of clay. During the firing process of pottery production, these elements melt and create a form of glass.
This newly formed glassy matrix acts as a glue that connects solid minerals together. Moreover, this process of embedding clay minerals in the glassy matrix is called clay vitrification. During that process, pottery becomes resistant to water.
The depending temperature at which clay is processed 3 main different types of ceramics are produced including earthenware, stoneware, and porcelain. Earthenware is produced at the lowest firing stoneware is in the idle while porcelain requires the highest temperatures for its production.
Additionally, there are some differences in the type of clay used for the production of these three ceramic types, which dictate some of the properties of final materials.
On my journey of learning about different ceramic types, I have spent some time traditionally making earthenware with local craftsmen (see more in this post), while I understood more about the porcelain and stoneware production from some of the fine ceramic galleries at my place(About which I will write more in my post on how porcelain differs from other ceramic)
Earthenware is the most common one used for cookware applications.
Clay minerals have a huge contact surface because of micropores in their structure. In Earthenware, After thermal processing below 1200C, clay saves a part of its porosity which gives unique properties to this type of ceramics.
In this article, I went deeper into the benefits of using earthenware(also called clay pots) where I summarized some of the conclusions and experiments that I did with utensils that I use for the last few years.
Compared to earthenware, stoneware, and porcelain, on the other side, are produced under higher temperatures. During this process, the clay mineral vitrification(turning to a glassy matrix) is more prevalent so they lose the porosity and some unique properties that come with it covered in the article mentioned in the previous paragraph.
Finally, it will be important to mention, that all types of pure ceramic cookware(earthenware, stoneware, and porcelain) can come in a glazed and non-glazed form which I will go deeper in the next subheading.
Not all pure ceramics cookware is left in the bare(non-coated) state. Some pieces are glazed, so the food doesn’t come in direct contact with ceramics. In this case, the glaze is the one that dictates performance and safety.
Ceramic glaze refers to a vitreous substance fused onto pottery through firing. The glaze has three basic functions. Firstly, it seals the inherent porosity of earthenware vessels rendering the vessels suitable for holding liquids. Secondly, it gives ceramics a tougher surface. And finally, glazes enhance the underlying texture or design painted, carved, inscribed, or unmodified.
Here is one picture to help differentiate the appearance of glazed and non-glazed earthenware
Basically, bare ceramics(either earthenware, stoneware, and porcelain) is rough under and it doesn’t have a shiny luster appearance.
You can easily observe the difference between glazed and non-glazed ceramic by taking the ceramic plate in the kitchen(They are in most cases made from glazed stoneware or porcelain) and turning the downside of the plate. You will observe that the plate bottom that is in the contact with pad is not glazed. This little exercise will help you feel the difference between what glazed and non-glazed ceramic looks and feels.
Finally, when you see some piece of pure ceramics painted on the parts that are intended to come in the contact with the food (e.g. inner side of the dish or cookware) or prints on them it is glazed in most cases.
But maybe you would ask, what are glazes actually made from?
Pottery glazes consist of three basic components which are applied to the surface of the ceramics (usually) in form of a dry powder which is fired together with ceramics and melted to form a glaze. First component counts for, glass-forming substances (silica or boron trioxide)(1.).
The second component is stiffening agents (alumina), which prevent a glaze from being too liquid when melted and staying on the surface of the ceramic piece.
Lastly, a flux component is used to reduce the melting point of glass-forming substances like silica, which has melting point(1710 C) much higher than the temperature used in the ceramic firing kilns
Finally, other additives are mixed with these basic components. They provide the color, determine glaze opacity and create other desired finishes.
To create proper glaze mixtures that contain a balanced amount of silica, alumina, and fluxes different naturally derived minerals are added. These minerals can contain one or more of these three main components used for ceramics. Sometimes, purified silica, alumina, or fluxes are also in use.
Some of the examples of commonly used maturely derived minerals are Flint(source of silica, alumina, and fluxes) BALL CLAY(source of silica and alumina), KAOLIN CLAY(source of silica and alumina), and FELDSPAR(source of silica and alumina as well as Fluxes in small amounts)(1.).
Here is the picture of raw materials for ceramic and glazes that I saw while visiting one of the retailers in my country.
.However, not all cookware that contains the word “ceramic” in its name is made from real ceramic in it glazed or non-glazed. Apart from pure ceramic cookware explained above, there is ceramic-coated cookware, that is just advertised as ceramics but it does not contain this material.
So let’s see more about it.
What is ceramic-coated cookware and how it differs from real ceramics?
One type of cookware is particularly advertised in the last decades, and it is ceramic coated cookware also known as non-stick ceramic cookware.
Ceramic-coated cookware is made from a few millimeters thin metal base(usually aluminum or stainless steel) unlike pure ceramic cookware where the utensil body is from ceramics which is quite thicker(usually more than half cm).
In the ceramic-coated cookware, the base is covered with one or a few layers of silica(silicon dioxide) which is applied in thin layers on top of the metal base through gel sol technology. (See details in the next chapter). Because of this ceramic non-stick coating is sometimes called gel-sol coating.
This coating has a ceramic-like appearance, but it is not made from real ceramics. This is why it is commonly called,” ceramic-coated” cookware.
*If you are interested in a few additional tips on how to recognize the difference between ceramic-coated and pure ceramic cookware, take a look at this post.
Finally, maybe you would say okay I see the point that bare ceramic cookware(earthenware, stoneware, porcelain) differs from ceramic-coated cookware.
However, what is the difference between ceramic-coated and glazed pure ceramic cookware when it comes to their interaction with food?
The glaze used on pure ceramic cookware is kind of similar to ceramic coating since it is also mainly made from silica(silicon dioxide)?
Here I would distinguish a few key differences. Ceramic glazes are made of silica, but also some other minerals (see the first subheading), melted together at high temperatures (e.g. 1000-1200C wor earthenware)
However, gel sol coatings are made from pure synthetically produced derivatives of silica(See next subheading), which can join together and form a much thinner coating. Additionally, unlike the glazes, ceramic coating is made at lower temperatures.
The differences in the materials used and the ways how gel-sol coating and ceramic glazes are made result in different physical properties of these two coatings. Gel-sol silica coating has much higher nonstick performance compared to ceramic glazes.
However, ceramic glazes are much thicker than gel-sol silica coating on ceramic-coated pans. I found sources that mention the glaze thickness of 0.5mm while the ceramic nonstick coating is measured in micrometers or nanometers(see pages 6 and 7 of reference 2.).
The very low thickness in gel-sol silica coating is much more susceptible to damage and less durable. Additionally, after a relatively short period ( less than a year) ceramic coating losses its nonstick properties, which is one of the biggest advantages of using it.
If you are more interested in this, you can take a look at my post about the durability of ceramic-coated cookware where I have collected some information from personal experiences about how much non-stick ceramic cookware lasts.
Finally, it will be important to mention the difference in safety aspects of these two types of cookware(Ceramic coated and pure ceramics). Since the nonstick ceramic coating is easily damaged the metal base of cookware can come out.
In this post, I have summarized more data about the ceramic coating cookware safety.
Finally, In this post, I have covered the topics on how safe pure ceramic cookware(both glazed and non-glazed) and how to avoid some of the health concerns that can come along with low-quality non-certified products. Pure ceramic cookware can generally be very safe in contact with food when it is properly chosen.
How ceramic coated cookware is made? What is a ceramic coating made of?
Ceramic-coated cookware, covered with white non-stick coating through gel sol technology is often advertised as ceramics even if it is not related to this material as presented in the previous chapters.
But is actually gel sol technology and how ceramic coated cookware is made?
The name sol-gel derives from a process where microparticles or molecules in a solution (sols) agglomerate. Furthermore, under controlled conditions, these molecules/macro particles eventually link together to form a coherent network (gel). (3.)
The gel sol process has a wide number of applications from coating electronics to different components in cars. A range of molecules is used for the coating. However, in cookware production, a chemical derivative of silica called tetraethyl orthosilicate (TEOS) is commonly applied.
To present how this substance forms the non-stick coating on ceramic-coated cookware as simply as possible I made a chem below. You can imagine silicone atoms that like grey balls able to create four connections with other atoms around.
In the TEOS molecule, the raw material for ceramic coating, these connections are made towards green balls(ethyl groups).
To make the net between silicone molecules which creates the final coating the connection with green balls first needs to be broken. This is done through exposure to controlled Ph and temperature conditions.
During that time the split connections between silicone and green bales are replaced with direct links between silicone molecules, through which the silicone net is created.
The whole reaction is happening in the water or another liquid, so after finishing the reaction between silicon atoms the liquid is evaporated, and the silicone layer is left on the surface to build up the thin coating.
The great thing about the TEOS is that during the polymerization process silicone molecules also link to the metal atoms on f the utensils which provide a good adherence between the coating and the metal base.
To make a more resistant, thicker coating on cookware, this whole process is repeated several times. However, the final coating is quite thin( few micrometers usually)
Unlike real ceramics production which commonly involves temperatures over 1000C(which triggers requirements for energy input and thus increased costs), the ceramic coating process can be done at much lower temperatures and thus it is cheaper.
Finally, to apply the microparticles of TEOS(or other molecules used for gel sol), different techniques are used.
An example can be Dip coating where the substrate to be coated is immersed in a liquid and then withdrawn with a well-defined speed or spin coating process, the substrate spins around an axis that should be perpendicular to the coating area(1).
In the cookware industry, Spray coating is commonly used where the microparticles of the TEOS are sprayed over the metal cookware body before the reaction. Spray coating allows the increase in the process speed and reduction of the sols waste which has contributed to the wide use of this technique.
To demonstrate the whole process in reality you can take a look at the video below.
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