When I moved into my house I did not have any grass. A light rain storm moved through the area moistening the surface of the dirt.
As I walked across the surface, I collected large amounts of mud and clay on my shoes. It was ridiculous.
Ever since then, I have had the desire to create pottery from the clay in my yard. People have done it for thousands of years. Seems like I should be able to do it.
To learn how to do it, I employed an age old tradition: I watched a documentary on youtube.com, googled some stuff about primitive pottery and clay harvesting, and set out to give it a shot. The links can be had below to the source articles.
Step 1: Harvest the clay
I tried two methods. The first was the dry method. I created a sifter by drilling small holes in the bottom of a flower pot. I then ground clumps of clay into dust while sitting on my front porch and sifted it.
Grinding the clay
I also tried the water method by swirling dirt in a bucket, allowing it to settle and pouring off the clay suspended in water. I then strained it in a towel and hung it up to dry. Both methods worked, though the water method yield a more even, finer clay. I also got a larger quantity of clay from the water method than I did from the dry method.
Step 2: Get the Clay Wet
If you are using the water method, then disregard this step.
For the dry method, I kneaded water into the clay as I would a loaf of bread.
The ball of finished product
Step 3: Testing it out
This is the test pot I created.
Firing different clay to different temperatures yields different results. I used a propane grill. According to wikipedia, the hottest a propane torch can get in air is 3,623 °F. That seems pretty hot, but I am pretty sure my grill is not as hot as a torch.
When firing clay, there are stages through which the clay passes. You can read all about it here, but I will summarize below.
Stage 1: Atmospheric Drying
Even after you let your clay dry, it will still contain some moisture. By the time your pot reaches 212 ºF the moisture will have been driven out.
Stage 2: Burn off Carbon and Sulfur
Between 572 ºF and 1470 ºF the carbon and sulfur will burn off.
Stage 3: Chemically combined water is driven off
Even after the atmospheric water evaporates, there is about 14% water chemically bonded in the clay. At this stage, it will be removed.
Stage 4: Quartz Inversion
Or Silica, if you are a potter. Quartz’s crystalline structure changes at specific temperatures and is called an inversion. One of these inversions happens about 1060 ºF.
Stage 5: Sintering
Clay particles begin sticking together at about 1650 ºF. This sticking together is called sintering. After a pot has sintered, it is no longer clay, but a ceramic material.
Stage 6: Vitrification and Maturity
Crystals form and bind the material together. Materials melt and fill in the gaps in the body.
Different clays mature at different temperatures.
So, how far did I get with my tiny pot?
I placed mine right in the fire of my propane grill. I did not have a temperature gauge that goes high enough to measure exactly how hot it got. The pot did hold water when it was done, but it was not very strong. I am not exactly sure why, but my guess is that I did not get it hot enough, or I did not leave it in the fire for long enough.
The final product:
For my next attempt, I am going to try a more robust firing solution using charcoal. It can burn at temperatures up to 4800 ºF. This should be more than hot enough to fire my clay.
This looks neat too. I think I will try this next time I go camping.
I pit fired my pieces. Check it out here: Finishing my Primitive Pottery.