Everything You Need to Know About Porcelain

When many people think of The Bright Angle, porcelain may be the first thing that comes to mind. That's because we talk about it. A lot. So, what makes porcelain so special? Let's unpack this.

What is Porcelain?

Alright, chemistry nerds, get ready for the nitty gritty! 🤓  We choose porcelain for The Bright Angle for its ability to be mixed into as liquid slip and formed by plaster mold parts that capture the negative form of the plaster mold. It can pick up even the most subtle texture and create volumes. This method is known as slipcasting.

At TBA, we have done hundreds of tests to blend raw materials together. Thankfully, the ceramic art community is packed with educational opportunity. Masters of ceramic craft have shared valuable insight into their experience with different translucent porcelain recipes. They've shared their problems and how to solve them. To name a few; Ben Richardson, Matt Katz, and Jonathan Kaplan, have been a huge influence. We highly recommend taking the Ceramic Materials Workshop with Rose and Matt Katz.

First, we start with the whitest kaolin and halloysite available (this is the plastic clay component) for strength and workability. We have experimented with adding a white binder to extend the plasticity and workability of the halloysite and kaolin which are the only plastic materials in the recipe ("plastic" meaning malleable). A good test to see how plastic a clay is to make a small coil and bend it, watching at what point it start to crack and break. These plastic materials containing the majority of Al2SiO3 are what make ceramic ceramic.

We add silica (glass or flint) to our plastic alumina source to make the porcelain transparent, highly structured and more refractory to the temperatures we are firing to. The silica source that is most readily available has the most iron of all of the materials we use, even though it claims it is 99.999% SiO2. This is ironic for us, because iron makes clay dark and opaque (even porcelain). So in order to alleviate the need for silica, we add fritted glass which contains boron and other fluxes that are stable and predictable, because they are smelted and then milled to a powder. Almost half of our porcelain recipe comes from within 100 miles of Asheville NC. We make art with The Blue Ridge Mountains.

Finally, we add feldspar to extend the maturity range (or to reach its peak strength), but to also encourage the kaolin and silica to melt to a glass while keeping their shape in the hot kiln when the forms are pyroplastic (they get bendy!)  Some have described porcelain as a structure having kaolin bones fused to a mass of glass by fluxes. A matrix of mullite, cristobalite and quartz results from heat and time being applied. The bone structure helps the pieces keep their shape while it is pyroplastic at high temperatures. Glass melts to a fluid amorphous state but by introducing kaolin in place of fluxes the material will not become liquid until it reaches high temperatures (we're talking a couple thousand degrees Fahrenheit!) Pretty cool, right?

Where Does Porcelain Come From?

So, here is why we chose porcelain for our lighting. Our goal was to make ceramic vessels glow. Only porcelain can do that. Porcelain is the most refined ceramic material for utilitarian tabletop and home decor products.

Porcelain is not only stylish, but is typically used for engineering purposes. Ceramic engineering actually refers to forming with inorganic, non-metallic materials. Alumina oxide is a refractory, high melting point, chemical compound that is utilized for its crystalline structure and hardness, as well as heat resistance for knives, spaceship tiles, bulletproof vests, crucibles, for smelting other materials, and much more Kyocera. 

So porcelain is not just another clay body - it's precious. For centuries the technology to create porcelain caused world wars between the East and the West. [For more on the history or porcelain, see "The Arcanum: The Extraordinary True Story"]

What sets porcelain apart from other clay bodies comes from a mixture of the ingredients mentioned earlier. The first discovery of raw materials containing this unique and valuable mineral combination was on Mount Kaolin in China. This geological phenomenon explains the command the Chinese have over ceramic manufacturing. Whole cities were founded based on this discovery of porcelain! Other steps that allowed the Chinese to be porcelain pioneers is their engineering expertise to invent machines to mine and mill the porcelain rock to a formable plastic material when added to water. They had the expertise and tools for shaping, forming and manipulating the clay or porcelain, along with the ability to heat the material into the glassy stone-like material we know today.

This required the construction of well-designed and well-built kilns: structures designed to hold heat through the introduction of fuel and air with efficient combustion. They burned wood and coal and fired brick and stacked brick into kilns designed to encourage complete combustion and keep their structural integrity as they were heated to white hot temperatures for days. The rest of the world did not have the luxury of having a mountain made of porcelain. They lagged centuries behind on finding the right combination of materials to make porcelain. Not to mention, they lacked the kiln technology to fire their porcelain to a hot enough temperature to meet the standard set by the Chinese.

Many take porcelain for granted because white ceramic tableware is everywhere; however, forming a quality porcelain recipe from scratch, even today, with the materials currently available in America is fairly difficult. I myself avoided porcelain for a long time, instead opting for darker clay for the workability and the deep colors that can be achieved. I began using porcelain in 2013 for its unmatched castability and strength and heavy use for tableware in restaurants and the home.

My appreciation grew as I accepted the process of slip casting for forming and the white canvas it provided for bright glazes. It is an elegant material that requires experience with clay to control. I like the challenge of controlling it. Controlling porcelain chemically is simple in theory, because it reaches body maturity at a high temperature with a very simple combination of raw materials without variability. On the other hand, darker iron-rich clays have impurities and organic materials that drastically influence firing temperatures and stability.

Testing Translucent Porcelain

My favorite quality of porcelain is in its ability to be translucent. Porcelain was once described to me as a glass with a bone structure of white clay. The ratio of the materials discussed earlier yields varying results, so it is necessary that we do many blend tests with controlled variables to learn what characteristics each material has when combined with others. Here at The Bright Angle, the greatest challenge we've had while making our porcelain translucent is bloating, which happens when the glass melts beyond its full body maturity. When the melting exceeds body maturity, it becomes less dense and begins to delaminate and expanding causing bubbles and micro gas pockets in the porcelain and it loses structural integrity. So, there is a sweet spot between materials temperature and time to achieve the perfect melt. Our objective is to melt the porcelain as much as possible, leaving as much glass in the ceramic as possible, without it melting into a puddle.

When the combination of materials reach a certain temperature, they achieve maximum density, max shrinkage, with the lowest porosity. The contaminants that can affect bloating are iron and titanium. For all intensive purposes let us just say that iron acts as a flux above 2000 degrees as well as turning porcelain a warmer color such as yellow orange red or black. It is just a mysterious material with many applications, but if we are trying to avoid variables and control the whiteness, we have to remove the iron. We use rare earth magnets that pull the iron out of our powder as we mix it. This also prevents small black specks of spotting iron.

Titanium on the other hand is quite refractory, and hard to remove. But its crystal structure introduces grain boundaries that cause the ceramic to be translucent rather than completely transparent. So we chose to work with raw materials containing as little of the two as possible. As a result, we get a nice warm glowing white glass. We have invested so much time and testing to achieve a recipe that is as refined as we can possibly make it.