How To make Terra Sigillata

What is terra sigillata?

Terra sigillata is a very smooth, lustrous coating of clay which resembles a glaze and is virtually waterproof. It is essentially ultra fine particles of clay suspended in water, which helps fill up the tiniest of pores on a bone dry clay surface. This allows for a mirror like finish if burnished properly. The name Terra Sigillata means “sealed earth” and has been used to refer to the Classical Greek Attic black-figure and red-figure painted pottery.

How Do You Make Terra Sigillata?

Making terra sig is easier than you may think. Let’s start with a list of materials needed and then we’ll go through the process of creating your first batch.

Supplies:

Mason Jar x2

Sodium Silicate

Siphon Hose

Making Terra Sigillata

Step 1

Find an area that you don’t mind getting messy. Also make sure that this place can be undisturbed for 24 hours as it will take a day for everything to settle before you can extract your terra sig solution.

Step 2

After finding a nice place, take a mason jar and begin filling it about 1/3 of the way up with dry clay. DRY CLAY is key here, wet clay will not work.

For this method, it does not have to be exactly 1/3, just eye ball it the best you can. Ball clay, or extremely fine clay that you have sieved through different meshes will work best for making terra sigillata.

Step 3

Add water to the mason jar, again when looking at the jar you should see about 1/3 clay to 2/3 water. The dry clay will break down quickly, shake or stir to quicken the break down.

Step 4

Add two drops of sodium silicate (yes really, you don’t need much at all, but there are many different uses for sodium silicate in pottery so don’t worry if you have a lot) to the mason jar mixture of water and clay.

Step 5

You will begin to notice an immediate change after adding and mixing in the sodium silicate. After mixing you will want to keep this mason jar on top of some books or bricks to keep it elevated for the next step. Make sure that you do not disturb the mason jar once it has been placed down. Let it sit for 24 hours and then come back to it to syphon off the layer of terra sigillata.

Step 6

Come back the next day and identify distinct layers displayed in your mason jar. There will be a layer of water, which is the lightest of the layers so it will naturally be at the top. The layer underneath that is terra sigillata. Underneath terra sigillata is a mixture of sand, silt and slip, unless you used store bought clay, which usually has all of the bigger particles out only leaving slip.

Step 7

Find the terra sigillata layer and place your siphon just before the transition from terra sigillata to slip. This is where you’ll want to siphon from, as it will pull the terra sig layer the most efficiently. Make sure to measure out the distance from the extraction point of one jar to the insertion part of the other jar. As you begin siphoning the terra sig, and it starts to disappear, keep an eye on the layer above (water) and the layer below (silt, sand, slip) and make a mental note on when you should kink the hose so that none of these other layers mix with your terra sig.

Step 8

You should be left with a layer of water and a layer of slip, silt and sand in one of your mason jars. The other mason jar should be filled with fresh terra sigillata.