Mars Clay

Martianware Covid balls the day after they were made

If you're a fan of space exploration, the most recent Mars rover, or clay, you might have heard that Seattle Pottery has made and is selling "Martianware" clay, a clay based on the chemical composition of soil on Mars. The idea is that if Mars had clay, this is what it would be like. Or maybe the idea is that people doing pottery think this would be amusing.

A freshly made Covid ball next to ones made yesterday.

As a potter, I found this amusing. If only to delight the 12-year old version of me, I bought some of this clay to play with. The wet color and even the texture does remind me of the surface of Mars that I made in elementary school for a science fair, though that was made of plaster and paint, I believe (and later was turned into a toy golf course after it sat in the basement for a while).

A freshly press molded bulb after being smoothed with a rib.

The clay is a low-fire, self-glazing clay, a bit like Egyptian faience. The materials in the clay include soluble salts inside the clay body. These salts react during the firing to form a glaze without needing to add glaze to the surface of the clay. This is similar to salt firing, where salt is added to the kiln during the firing. The salt adheres to and reacts with the surface of the clay, creating a slightly bumpy glazed surface.  

A bit of salt inside the raw clay

The clay feels very strange to work with. I only bought a small amount and this weekend I made some of my Covid balls shapes with it, as well as a couple of press-molded bulb forms. The clay is stiff and tends to want to crack, though it can be smoothed. It's work-able, but certainly not the most pleasant clay I've used. As I was cutting into my small block of clay, I encoutered several fairly large chunks of salt inside the clay block. I assume these pieces of crystalized salt had developed between when the clay was mixed and when I worked this it. I was easily able to crush the pieces, but they were large enough that I jsut removed them from the clay I was building with.

A press molded bulb resisting removal from the mold

It was fairly easy to build the hollow forms, but the clay did not want to be press-molded. Usually I can press clay into my plaster mold, leave it for 20 minutes and it just pops out. Though this clay already felt drier than usual when I put it in the mold, I couldn't get it out of the mold until the next day. After I tried it, I started wondering whether the salt of this clay was actually bad for the plaster of the mold. 
 

Thrown saggars for firing

I'm also slightly concerned about the elements in my kiln. Salt firing is only done in hard brick kilns fired by gas or wood because the firing process destroys electric elements and the soft bricks of most electric kilns. In fact, firing a non-salt firing in a kiln normally used for salt firing may yeild strange results, as the bricks themselves contain residual salt. For this reason, I also threw some containers to use as saggars, ceramic boxes to contain the clay. Firing the pieces in saggars should protect the kiln from the worst of the salt, but I think I'll double check Seattle Pottery's recommendations before firing, regardless.

Martianware Covid balls drying

The immediate change in the clay is interesting. I made some of the pieces last night and already this morning they've developed a salty fur over their surfaces. The salt is growing on the surface of the clay. It looks a bit like mold, but feels brittle and crumbly. 

my studio assistant was recently asked not to walk on my wet teacups

As I've gotten into the sudio fairly regularly over the last few weeks, its looking like I'll have a chance to fire fairly soon. Yesterday I mopped and cleaned all the tables, cabinets, bats, and my mixer. It's amazing how good it feels to work in a freshly cleaned studio.