Making Potash

"Potash" is a vague term referring to any of a variety of soluble compounds of alkali metals, mostly potassium carbonate, potassium chloride, sodium carbonate, or sodium chloride. All of these compounds can be found in burned plant ashes as a portion of the leftover non-flammable, non-volatile material left after burning.

I desire potash for one reason: it acts as a flux for silica compounds. I will use this in two different other projects. First, as a glaze for pottery that can melt and seal ceramic items without the underlying item melting, thus allowing me to waterproof earthenware mugs and pots. Second, to lower the melting point of quartz for making glass at reasonable temperatures.

When you burn things to create ashes, though, a lot of other substances also end up in ashes:

Iron oxides
silicon oxides

aluminum oxide

calcium oxide

magnesium oxide

manganese oxide

phosphorus oxides

unburned charcoal

The ratios of these and potash depend on the species burned. Willow wood yields a whopping 50% potash, and very little silicon or aluminum. English oak yields 23% sodium and potassium compounds. Rice husks only provide 1.3% potash, etc. I am using leftover ashes left over after other clay project firings, and I don't know the species. This is bad for achieving a consistent pottery glaze. Later, I will want to source a consistent supply of ash, but right now I'm happy with ANY result.

The best way to separate our desired potash from the other substances in raw ashes is to exploit potash's solubility. So first, we shovel some ash into a container, (I strained through a cheap spaghetti colander first to get rid of large chunks), flood it with water, and let it sit for a couple of days. It will look like this:

In the photo, the liquid on top is full of potassium, sodium, hydroxide, and carbonate ions, which we can now pour off into another container for further processing. The solids at the bottom are the non-soluble oxides that would ruin the melting point-lowering properties of the potash.

Don't get greedy. Don't pour off the liquid before the solids have settled, and stop pouring when you start getting any ashes pouring out. The non-soluble ashes will be counter-productive, because they are highly refractory and will raise the melting temperature of whatever you're making.

Careful, the poured liquid is highly caustic. It is not a cellular poison in the sense that something like cyanide is, but it will chemically "burn" you (turn your skin into soap) if you get it on you and don't wash it off quickly. Wear eye protection and gloves when pouring, and flush any splashed skin with large amounts of water. Treat this liquid as essentially Drano.

By the way, save the byproduct solid ashes. For two reasons: One, you can refill with water and repeat the process again for more liquid from these several times. Two, once you're all done, the remaining washed ashes are wonderful for making fire bricks for furnace linings, because all the remaining materials are very resistant to heat and have very high melting temperatures.

Anyway, back to the liquid: letting this air dry is ineffective, because crystals will start covering the water surface and prevent evaporation. Boiling the water off works better. The amount of water you see at the top of the jar poured into a pan and boiled dry yielded this:

Again, these crystals are caustic. They will re-dissolve and saponify your skin if you get them on you with any moisture (like sweat). Be careful. That said, I unceremoniously scraped mine off with a spatula. The potash won't ruin your utensils or pot, and you can use them for food later, as long as you VERY thoroughly rinse and wash the potash off first. Tiny trace remnants that remain after going through a dishwasher or a good scrubbing will not hurt you, they are not toxic beyond being strong bases. Think of it like having Drano or bleach in a pot temporarily -- you wouldn't throw out the pot, but you would wash it well before cooking with it.

At the end of the day I disappointingly ended up with this much potash from one pouring of the container liquid:

These aren't exactly fluffy white crystals, but that's okay. It might be just that there are several compounds mixed here, so they inhibit one another's crystal formation. Since all of the hydroxides and carbonates are useful, though, this is not a problem. We don't need to separate or purify them individually (also, the crystals are still damp in this photo).

Don't put the potash on aluminum foil. It will react.

This is only one pour off the jar of ashes. You should be able to continue getting potash for many pours in a row, leave a day or two between each one, until you stop getting justifiable returns. My second pour-off a couple of days later yielded about 75% as much as the first, for example.

The potash will lower the melting point of clay it is mixed with. So when mixed with crumbled dry clay, ground up, mixed with water, painted onto a piece of ceramic, and left to dry, the surface mixture will melt sooner than the underlying clay piece, creating a glaze. I will cover this topic in more detail in a future blog post, but I have already achieved early success in using my potash to make glaze. The black corner of the right side piece in this photo is vitreous glaze made with the above crystals and clay powder. If/when I can cover a whole piece with successful glazing like this, I will be able to make waterproof items:

Homebrew Pottery - Firing local clay

SO! I have now found some local clay and I have figured out the best amount of tempering to use. I also mixed up my pure clay with some different additives for the purposes that I wanted.

Now it's time to fire the clay into true ceramic! Several processes are involved, but mainly, the firing process mainly drives out water (only some water evaporates, and the rest is physically trapped or chemically bound), burns off organic material, changes the crystal structure of quartz components ("quartz inversion"), and sinters particles together.

My "kiln" at the moment is nothing but a Weber grill. The temperatures on the rack where you would normally put food only get up to maybe 600-800 degrees, but by completely burying clay wares in charcoal, the temperatures can get up to the roughly 1800+ degrees needed to begin to make true, low-fire earthenware ceramics (bisque temperature). The whole heating process needs to proceed SLOWLY. For more information, google "firing schedules." Details are beyond the scope of this blog, unless people are interested.

I'm firing simple bricks for now, to be used later as kiln components for a proper homemade ceramic kiln. The orange bricks in the photos are ones I fired earlier, and have painted with a homemade ash glaze as test pieces for glazing. This is simply part potash and part local clay, mixed with water and painted onto the pieces then left to dry in place. You can see the grayish ash on top of them (see future blog posts for more details).

First, I heat up the bricks around the outside of the grill, as the coals are lighting. This very gently brings them up to ~150 degrees over the course of half an hour to an hour, driving out as much water as possible without creating expanding steam that might crack the pieces:

Next, I move the bricks into hotter and hotter zones, eventually leading to a pile in the middle. This brings them closer to maybe 400 degrees, driving out the last bits of chemically bound water.

I remove the grill and very quickly (lest the pieces start cooling off) add more fresh charcoal to the fire to make a nice bed. I pile the pieces back on top of the new charcoal bed and leave them there for maybe another half an hour or so. You can see in one of the photos below that open flames are visible from organics burning off, and the bits of grass are charring away. this is somewhere between probably 600-1000 degrees. 

I did this part too quickly still and caused some black charred-looking areas, which is a sign of too little oxygen and too quick of organic fuel consumption (it has to do with the iron in the clay body reducing), but oh well, lesson learned for next time.

Once most of the organics looked burned off, I covered the pieces entirely with a layer of lump charcoal. This decreases oxygen access, so AS SOON AS POSSIBLE they need to have a forced airflow added to them at this point, or further "black coring" will occur, which is bad for your clay. I had a box fan pointed at the fire when I did it at this point, but this was probably not enough.

The upper charcoal is lighting, and you can see the red-hot core of the inside part of the grill where the pieces are. Open flames are still visible, but at this point I wouldn't be too concerned about it being organic material, it's probably just the charcoal itself. This is dull to cherry red glow around 1500 degrees maybe at this point:

The firing continued into the evening hours. The internal temperature is now sufficient to create bright red to orange hot ceramic pieces inside, as you can see in the photo where I briefly lifted the lid off to show a brick inside. This bright orange to almost yellow glow is probably somewhere around 1800 (+?) degrees. During this time, I was blowing air into the fire from a squirrel cage electric powered fan, positioned underneath through the ash collection hole, firing oxygen up through the fire. I got lazy and was inconsistent with this, but it really should have been going continuously, all the way until the fire burned down, if I wanted the strongest pieces. Since I let it go without forced air for awhile, it further reduced more of my clay's iron and made the pieces more brittle than they should have been.

This temperature was held for maybe another hour or so, adding charcoal as necessary. After that, I let it die down on its own all the way until cool (several hours). Then I removed the bricks and took the photo you see below. The bricks have been successfully made into true ceramic, with their oxidized iron components giving them a familiar brick hue. The especially light color is no doubt due to the sand mixture I added.

The gray/black spots you see are reduced iron from me being impatient with my firing schedule and not using enough forced oxygen. These reduce the strength and effectiveness of the bricks and are to be avoided.

Generally, the bricks were very brittle, probably too brittle to use. Not just from black coring, but from probably using too much sand and grass clippings in the mixture. Just from touching them, it is OBVIOUS though that they have huge insulation value. The bricks are very lightweight and very porous from the burned away grass, almost like pumice. All those tiny air pockets make them more effective at insulation, at the expense of fragility. These need a higher percentage of clay overall, because the balance is too far toward fragility, but it's a minor recipe tweak.

The other three pieces were ones that were fired earlier, and simply had glaze applied to them. You can see how they hold specific shapes much better and have little or no porosity, because these pieces were 100% clay in composition (on the inside/main body). You can also see how they are redder in color due to higher iron content when sand and grass are not mixed in.

The glazing experiment was a partial success. From left to right in the image below, glaze mixtures with a lower ratio of clay slip to potash are shown. The highest clay content on the left strangely seemed to have burned away completely, or perhaps got scraped off by accident, this one is confusing. The other two are as expected: the medium mixture in the middle looks like I just painted more earthenware right onto the block. This is no true glaze, and won't help to keep water out, etc.  But the high-potash content piece on the right shows signs of JUUUUUST beginning to form an actual glaze in the upper left, and a near-glaze (white) elsewhere. The black corner is actual glass, and is proper, waterproof glazing!

Getting the whole piece to be consistently covered will require a combination of just a slightly thicker coat of glaze painted on, a couple hundred more degrees of temperature, and probably more potash in the recipe. The more potash you add, the lower the glassifying temperature, but the more fragile and likely to crack (and harbor bacteria) the glaze is, so this is a careful balancing act, but I feel confident now that an actual waterproof glazed mug is within my abilities!

Next steps include making a more proper kiln with insulative lining to get hotter temperatures, adding better airflow and oxygen control throughout the process, and fixing the glaze and brick recipes.

Let's Build an Organ Pipe!

Part one here!

In this post, I'll go step by step through my process for creating an (unpainted) PVC organ pipe! An organ pipe has two parts: the resonator, which is most of the length of the pipe as a simple empty tube, and the fipple, which creates oscillations.

THE RESONATOR 

The resonator takes vibrations (or perhaps more accurately, oscillating air vortices that I don't entirely understand) from the fipple and resonates at a fixed, controllable wavelength, allowing specific tones for music. Each pipe is going to produce one fundamental tone, just like individual strings in a piano. A single pipe will create several other tones at once when sounded, equaling integer multiples of the fundamental frequency (harmonics). The smaller the pipe, the more prominent the harmonics, but the fundamental is always the strongest.

Here are some different harmonics fitting into a single pipe (top three waves) and a fundamental of a longer pipe (bottom), with distance from midline being relative min and max pressure for each one:

However, less so than composers, we don't need to concern ourselves much with harmonics for building the organ. The pipe will sound like the fundamental frequency when you play it. So what matters more for us is the bottom of the image above: When you make a longer pipe, it will naturally resonate at a longer fundamental frequency. Longer waves are heard as lower tones. So by making different length pipes, we make different notes.  One half the length of pipe = one octave lower, and other notes vary by even logarithmic steps in between. In other words, human perception varies logarithmically with frequency.

So the resonator, at the end  of the day, is just an empty tube of the correctly calculated length. I'm making mine out of PVC pipe. For tuning purposes, I also have slightly larger pieces of pipe on top that can slide up or down to make fine adjustments to the lengths for tuning.

Middle C is an open pipe of about 2 feet in length, as a point of reference. A concert tuner of the A above middle C at 440Hz is about 1.28 feet long. 

Closed pipes (with a stopper at the end) have twice as long of waves, roughly, because the wave has to "reflect" the length of the tube then back again from the fipple. A closed pipe sounds one octave lower than it normally would, so middle C would be about a 1 foot long closed pipe. This is useful if you want to fit big pipes in an apartment building.

THE FIPPLE

The fipple is the vibration producing part of the pipe. I'm going to be routing air to my pipes by plastic tubing, so it needs to convert a stream of pressurized air from a circular tube into a consistent vibration. The fipple is much harder to make than the resonator.

Briefly, the concept of a basic flue pipe fipple (meant to sound something like a flute) is:

1. You somehow shape incoming air into a laminar air flow (a flat, non turbulent sheet of air).
2. You get that flow to pass right into a thin knife of rigid material, which will then vibrate.
3. The vibration resonates in the resonating chamber.

The way we make those things happen is by building something like this:

The pipe (red) has a cap on the end (black) with a hole for the air hose (green). There's also a plug in the pipe (orange). Air comes into the cavity in the back and has nowhere to go, except for a narrow section of pipe cut away at the top. This forces the air into a sheet, which passes over and under a knife shape cut in the pipe (red also). This vibrates, which then causes resonation in the pipe (left off the edge of this image). Again, I think it is more like oscillations of swirling air systems in a much more complicated way than just vibrating, but that's close enough for me to build it.

So without further ado, let's build it! We begin with a PVC plumbing pipe:

First, we need to cut a notch out of the end. The width of the notch is related to the diameter of the pipe, something around 2/5 the diameter. The depth of the notch depends on the system you're using for a cap. I used this tool here, a dremel with a grinding fiber/ceramic/something wheel:

Here's the notch cut out:

Then I used a much wider grinding stone (seen below), 100 grit sanding drum (not shown) and finally manual 220 grit sandpaper (not shown) to grind a sharp, gradual "knife edge" on the inside of the notch. Grinding stone:

Knife edge after all the dremeling work:

Knife edge after hand sanding:

We need a laminar sheet of air now. I achieved this by using the thickness of the PVC pipe wall itself as a guide for a sheet of air. So I need to block off the inside diameter, AND the outside diameter. The inner diameter is blocked using this section of a solid plastic dowel rod:

The corner is sanded down to aid aerodynamics (the air needs to be smoothly guided toward the knife). The plug fits into the pipe snugly. Notice how the pipe walls stick above the plug, so that when the cap goes on later, there will be a thin slice of opening:

A hole is drilled in the middle of the pipe cap. This is where plastic tubing will go to deliver the air supply:

And finally, the cap is attached. If you look closely, you will be able to see the thin slice of empty black space in between the plug and the cap nearest the camera. This is the guide for the airflow to make it into a sheet of air. It will then pass right into the knife edge, creating the musical vibrations, which resonate in the remainder of the organ pipe:

Again, here's the schematic now that you've seen the real thing:

NEXT TIME

In the next installment of this series, I will explain how the air system works, and I think I'm going to actually try out a new idea, different than my original plan, for how to activate air flow to individual pipes. I will try experimenting with homemade electric solenoids, versus the alternative of manual springs and levers and things.  If the electric version works, then the whole organ could be played either manually OR by computer program, potentially!

Creating Homemade Refractory Bricks

"Refractory" is just a word that means "very resistant to high temperatures." In the context of pottery and glassmaking, I need refractory material for the lining of my kiln(s) I am going to make. Regular, pure clay doesn't cut it. I can also use refractory for making bricks to hold up pieces in the kiln or to use for making the actual walls of a kiln, if I want to make one out of entirely my own materials.

For either of these purposes, I need a substance that is actually not only refractory, but also insulating. That is, it should neither break down at high temperatures nor should it let heat get past it. Tungsten metal is highly refractory but a poor insulator. Cotton is not refractory (will burst into flames at maybe 400 degrees F) but is a great insulator.

Pure earthenware clay by itself is mediocre at both of these things by itself--it will slump and melt at moderately high temperatures, and it isn't actually that great of an insulator (Think about how quickly your mug gets too hot to touch on the outside when you pour coffee in it). So we want to improve these qualities for furnace materials.

Refractory recipes can get very complicated, but for mine, I want only locally available ingredients. I am going to have 3 ingredients: dry grass, quartz sand, and some of the clay I prepared earlier here.

• The clay forms the main body of the material and holds everything together. It is also, of course, reasonably heat resistant.
• The sand raises the melting point of the material significantly, since quartz melts about 500 degrees celsius higher than earthenware clay does (note: sand is locally available, but this particular batch used hardware store sand just for now). 
• The oven-dried grass helps hold everything together at first, since the clay mixed with sand is crumblier than pure clay (see here [link]). Later, the grass will burn away in the kiln and leave lots of tiny air pockets that will help insulate against heat transfer.
• ...another ingredient I could have added is wood ash. WASHED wood ash. I.e. the stuff left over after you have soaked new ashes in water and drained off the potash a few times (this will be the subject of an upcoming blog post, since potash is used for glass making and pottery glazes). Washed ash stuff is much more heat resistant than quartz, so replace a little or a lot of the sand with it, if it's available. It must be washed ash, though: raw ash contains potash, which is a chemical that actually lowers the melting point of quartz, and thus is counterproductive.

The ratio I'm using is about 50/50 clay and sand by volume and then about another equal part as the sum of the first two ingredients in dry grass by volume, loose (not packed!). In reality, it's probably something like 70/27/3 by mass for clay/sand/grass, but I don't know. It's easier for me to measure volume, so I'm just using that. Mix it all together, and you get something like this:

This is essentially adobe in it's raw form. You can build some pretty strong buildings out of this in dry climates if you let it bake in the sun for awhile, although you'd probably want more sand and grass in it.

The adobe is much harder to work with than pure clay, but making things like bricks is still easy. Below are some examples of bricks that I made out of this material and then fired (I'll cover firing in a later post). Click for a larger size. As you can see, the grass has burned away and left them porous. These things are super lightweight and feel like pumice, and their insulation is probably excellent. Unlike the raw adobe, though, the fired bricks are also extremely brittle and easy to break, since the binding strength of the grass has been removed and now actually hurts the strength of the material by leaving air behind instead. 

The examples below actually used more like 60/65% sand, 35-40% clay by volume, and the fact that they are so brittle is why I'm now suggesting a 50/50 mixture instead (I also toned down the grass slightly from these bricks):

Notice the gray spots all over -- there was not enough oxygen and/or not enough time during firing. This is the same issue as that cheap hardware store pot I showed in an earlier post. It's not the end of the world, but it does increase brittleness even further, and I need to fix it. I'll discuss this more in my post(s) about firing clay.

You can also see a crack in the middle brick that formed just from roughly piling them in this stack! That's how brittle these are with the sand-heavy recipe... Again, use more clay than this (which I will be doing in the future).

HELPFUL LINKS

Probably the most popular recipe for homemade refractory online is this one:
A version using perlite for insulation and cement as well.
It does not use local materials though. Even less local and not homemade are commercial versions:
An example of hardware store refractory.

My own version is adapted from commercial versions and the backyard metal casting website, but substituting locally plausible materials (the sand and clay are literally locally gathered) to fill all the same roles in about the same ratios.

Making a Homemade Pipe Organ

One of my long term crafting projects is to build my own working pipe organ. Do I know how to play the organ, you ask? The answer is no. No I do not. Why did you ask that? I hardly see it as relevant.

Moving on, this will be a "positive organ," or in other words, a small desk-sized one. In the layout below, the entire table there is about 4 foot by 2 foot, and the largest pipes are 2" in diameter and would just barely clear a typical apartment ceiling (top pipe in the splash image above). The color coding is for commercially available widths of PVC pipe, my primary building material:

I don't remember at all what made me interested in this project, but hopefully it will be capable of creating wonderful art when it's all done, whether or not I'm the one making art with it!

Overall, a pipe organ requires the following components, and thus these are the major areas of the project:

1. A frame of some sort -- this can be anything from a modified table to a huge gilded architectural wing of a building. In my case, my most important design consideration is portability - I am keeping the organ small and desk-sized, and I want to be able to break it down for transportation.
2. A lot of pipes -- My organ has five octaves (61 pipes) in flute-like sound, give or take a few pipes possibly for different harmonies at the end(s). One octave is a 2x difference in pipe length. You can "cheat" your way for one bonus octave without longer pipes by making ones with stoppers in the ends which effectively doubles the virtual length. Thus, my organ will have pipes from about 4 foot to 6 inches. They also get narrower as they get shorter. I am planning 2-3 additional redundant octaves in something much more fun. Tentatively, "bubble" sound. I.e. bubbling water, but in specific pitches. Because reasons.
3. A keyboard (called a "manual" on an organ). This doesn't have to have a key for every tone, although it is convenient and mine will. The color coded keys above are ones that would be able to play either/both bubble and flute pipes, based on a pull-control knob (a "stop").
4. A "wind" (air) supply, including some sort of fan or bellows, as well as a regulating reservoir to control for consistent pressure despite however many keys you are playing at once. Without a regulator, an 8-note chord would play 8x more softly than a single note. We want consistency, which requires building up a reserve of air pressure. i will use a squirrel cage electric fan and a box with a rising, weighted lid for a reservoir.
5. A windchest, which is an interface that takes in the main air supply, and uses linkages from the keys and any number of control stops to distribute wind to the appropriate pipe or pipes.I plan to take advantage of plastic tubing to greatly reduce the mechanical complexity compared to traditional church organs. Basically all I need are some small boxes and flap valves for each key, and some airtight gaskets, and that's it. Possibly one sliding board to convert between flute and bubble pipe voices.
6. Finish. Most of the pipes in my organ are going to be made out of PVC plastic plumbing pipe, so paint is a high priority to hide that fact. A tentative paint scheme is something like this (the arrangement of pipes here is not realistic, just slapped on the image):

(Possible paint scheme of my organ. An air pressure reservoir is on the floor. 

The tube sections on top of the pipes are tuning slides.)

In my next post for this project, I'll dive right into the design and airflow diagrams for individual organ pipes, which are all homemade here, mostly out of PVC.

In the meantime, here's a sound clip of the four pipes from the splash image. In order from the top: 1,2,4,3. Sorry, the highest note is a bit wheezy and cracks its voice--it's not the pipe, it's just that I can't play it as hard as it is designed for without blowing out the audio on my microphone. At normal strength, it is crisp.

HELPFUL LINKS

I'd like to extend deep thanks Raphi Giangiulio, who I have never written or talked to myself, but whose website about homemade organ building has been my #1 go-to resource for this project so far: Mr. Giangiulio's homemade pipe organ. Here's a sound sample using flue pipes similar in construction to what I have planned (mine would be less warm and rich): Giangiulio sound sample

Matthias Wandel's project has also been especially helpful as an inspiration: A less ambitious but still awesome homemade pipe organ

(I don't think either of these guys knew how to play the organ either, by the way!)

Homebrew Pottery - Tempering local clay

People in ancient Mesopotamia didn't have the luxury of driving over to Blick art supplies and buying a clay that had exactly the physical properties they wanted. When you dig your own local clay, you have to consider including additives to change how "plastic" the clay is, how strong it is versus how easy it is to work, how well it dries and avoids cracks, etc.

TEMPERING

"Tempering" clay is adding some amount of non-plastic material to a clay body to change its working properties. Namely, appropriately tempered clay is supposed to crack less easily and shrink less (which also makes it more thermally shock-resistant) than non-optimally-tempered clay. You can make temper out of:

• Crushed shells
• Crushed old bits of already-fired pottery
• Sand (if it has sharp-edged grains)
• Really, anything else that can take the heat of a kiln and that has particles with "bite" to them

For my temper, I chose crushed pottery, also called "grog." The pottery in question was a boring old terracotta pot from the hardware store. (The black core is because the manufacturers were cheap and fired the pot too quickly, so the iron reduced to a different oxide. It's fine for my purposes)

(By the way: I'm going to be "cheating" on my "from scratch" rule to start early on at various steps, only as I am learning. Like by using hardware store pots. Later, once I know what works, I will go back and do things like make grog out of pottery I made myself instead!)

MAKING THE TEMPER

First, I crushed up the pot between an old sheet for eye-safety (use goggles as well!). You'll probably have to re-fold the sheet over and keep hitting several times to get enough small pieces:

This leaves you with a variety of different sized bits at any given point. Once I had them pretty small, I poured a handful of them all into this burlap bag, to sift to a common size (I had no idea if this is the optimal size ... SCIENCE!), and sifted them onto a clean area:

This is now my (unusually fine) grog. Apparently people tend to use larger grain sizes than this, but I didn't know that at the time. I might get better results if I try again with a larger mesh.

TESTING THE TEMPER

But anyhow, the next step is to take some test clay and divide it into some equally sized bits. We are going to add different percentages of grog to each bit and see which proportion of grog gives us the optimal working characteristics for this particular local clay, going in 10% increments (I just did it by apparent volume). Here are my clay bits and grog before being mixed:

(Don't know why it looks ashy gray here. It's the same reddish grog as above.)

Once you have thoroughly mixed a set of 0% 10% 20% 30% 40% 50%, etc. balls of clay/grog, smash them into discs. Make note of how easy or difficult they are to work with while still moist.

Then wait for them to fully get bone-dry. This means "dry looking but also room-temperature when touched, which indicates no more deep evaporation is happening, either."  Whichever mixture cracks and shrinks the least is the proportion you want. In my case, any amount of grog seemed to be a bad thing (0% performed best)!

From left side, going clockwise: 60% grog, 50%, 40%, 30%, 20%, 10%, 0% (pure clay):

After drying, the situation hadn't changed. The pure clay didn't crack at all, and the tempered clays all got worse.

Since doing this test, I have tested another few mixtures for furnace lining (see future posts!) but all of my test items themselves are pure, un-tempered clay. That doesn't necessarily mean that's the best solution. If I were to be very thorough, I would want to test other types of tempers (shells? sand?) and also different mesh sizes of temper.

Homebrew Pottery - Finding and Refining Local Clay

In this long term project, I'm going to make a drinking mug completely from scratch. I will dig my own clay, make my own additives, refine my own high temperature fuel, fire it all in a homemade kiln, and apply homemade glaze then fire it again. In the process, I hope to get more fully in touch with all of the items and the effort that go into a single, simple tool in my life. This is a project about attaining a broader perspective.

Also... I get to play in the mud.

SO LET'S BEGIN! FIRST WE NEED TO FIND SOME CLAY

 

There are many kinds of clay, and you should be able to find some sort nearly anywhere you live:

"Earthenware" clay is easy to find most places. This is clay that has a significant number of impurities, notably iron oxides. As a result, it falls apart at lower temperatures than higher grade clays do. It also turns red when fired from the iron content (or black in an oxygen-starved environment). Earthenware won't vitrify (turn to a glass-like state during heating), so the products aren't waterproof unless you glaze them.

"Stoneware" clay (also called fire clay) is a purer clay that can be fired to much higher temperatures, where it can vitrify and be watertight naturally. You CAN also glaze it if you like. It is white or light gray in color and is usually deeper underground.

"Porcelain" clay (or china clay) is an almost pure "kaolinite" mineral of silicon and aluminum and oxygen, which allows for the highest firing, whitest, slightly translucent pottery wares. This is rarer than fire clay, harder to work with, and you're very unlikely to find any on your own.

Personally, I was only able to find local earthenware clay. Not too pretty right out of the ground:

For earthenware, just look around your neighborhood or yard for areas that LOOK like clay when wet (pretty technical stuff, I know). A good time to notice this is after a storm. Also check any bluffs/cliffsides/ravines that show you a cross section of soil. River or stream banks are also good bets.

Another method is to go to this website (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm), hit "start WSS," highlight your neighborhood as an area of interest, then go to the "Soil Data Explorer" tab and run a map of "clay content" - it asks you for a depth first, so choose something like 0-12 inches.  You will see a colored overlay of your neighborhood with % clay of nearby soils. Find a spot where you might get permission to dig that has a lot of clay, and start there!

Once you find what you think is a high clay content soil, get it sort of wet, and roll a "snake" between your hands about half an inch thick. Try wrapping it around a finger. If it wraps without breaking apart, then you have a good amount of clay in that soil. You can still work with lower content soils, it will just take longer.

NOW TO REFINE YOUR CLAY

Chances are, if you dug up some local clay, it's going to be impure. The process of purifying is pretty labor intensive, but also entertaining! You get to explore your inner child and go play in the mud a lot.

You will need: A couple of 5 gallon buckets (if you used one to dig clay, that counts as one), some twine or rope, straining cloth like muslin, a sieve or loose burlap, an old large spoon, and one or two nice wide wooden boards or a piece of plywood for drying.

1. With the clay in a 5 gallon bucket, pour in about 2 parts water for every 1 part soil you dug.
2. Use your hands to break up any big chunks underwater. You want the smallest possible sized bits of clay. Be careful NOT to compress clay together! This will will slow everything down, because water won't get to your clay particles as easily. Just loosely break up clumps, and swish water into all the nooks and crannies.
3. Let this sit for a full day (you may want to put a lid on it if it's outside, due to bugs and leaves and stuff). The smaller the bits you crumbled up, the faster the clay will "slake" into fully wetted clay water.
4. The next day, stir up the mixture just a bit to get settled clay off the very bottom. The idea is to get tiny clay particles in suspension again, but then wait just a couple of minutes for sand and silt to settle out again.
5. What you're going to do is pour the clay into some muslin or similar cloth to let it drip out excess water. A small scale version I did looked like this:
   
   
   
6. But it's more efficient to do everything at once. Since then, I've changed to 5 gallon buckets with muslin tied around their rims, with the water dripping into the bottom of the bucket. So tie off some muslin VERY SECURELY (4-5 tight wraps of twine, it needs to hold heavy weight!) around the rim of a bucket, leaving about a 1/3 bucket height worth of room at the bottom for dripping. Then position a strainer and pour your clay water through it into the cloth, to remove the floaters. As soon as you see anything other than clean, smooth looking clay water coming through, STOP pouring:
   
   
   
7. Discard everything left in the first bucket, which should be a bit of clay, lots of sand, rocks, etc. Also discard whatever the strainer caught (usually remaining floating things). From my small scale versions, this is what some of the leftover material in the bottom looked like:
   
   
   
8. You may want to repeat steps 4-7 if you still feel sand or sediment at the bottom of your bucket, but really it's not that big of a deal.
9. Around 1-2 days later, check on your clay. A lot of water will have dripped off, but it should still be fairly wet. If it is dry enough to spread onto a board without running off the side, then you're ready for the next step. Usually a "milkshake" consistency is enough to make it not flow off the board. If it is still too wet, let it sit another day. Note: the clay will compact a bit on the bottom near the cloth. It may look like pure water on top, but be milkshake consistency or thicker underneath still, and it might be ready. Check the actual clay.
10. Now take a spoon or your hands and glop your clay onto your wooden boards or plywood, and spread it maybe 1/2-1 inch thick. Scrape off as much as you can from the cloth.
11. Set the boards outside in full sun if available, and they will dry out the clay rapidly. A fan blowing over them works pretty well, too, at night, but sunlight is much less tedious. In sun, check every 10 minutes or so and remix if necessary to make sure that the edge clay isn't drying too quickly. With a fan, every 20-30 minutes. You don't want it to ever get crumbly-dry.
    
    
    
12. When the clay is of a good strong pottery building consistency, put it in a plastic bag or wrap in plastic wrap or similar, so that it stops losing moisture. Now you should be able to store it and treat it like any store bought earthenware clay. When it's all dry, it works just like commercial clay! Here's some freshly sunned clay:
    
13. Be sure to "wedge" your clay before building with it, like you would a commercial clay. If you don't know what I'm talking about, wedging means just mixing it together to make it an even consistency. There are many ways to wedge clay, and I can't explain them as well as online tutorials can. Check out several methods here: wedging/kneading methods. Then build stuff:

    
    (I know, I'm a masterful potter, eh?)

IN FUTURE POSTS

I will go over the remaining steps to making pottery wares (assuming I can get them to work!):

• Tempering the clay: adding crushed pottery bits, shells, or sand to the clay to make it less likely to crack. This requires methodical testing to find the right amount to add for a given clay.
• Making some sort of kiln: I will be attempting a wood or charcoal fired kiln to continue with the "from scratch, if possible" theme. In another post, I may also attempt making my own charcoal. Ideally, the kiln would be made out of homemade refractory bricks, but I might need a source of fire clay first, if I'm to do that.
• Firing the clay, and possibly glazing it usefully somehow, although I understand glazing is difficult to do with low temperatures and with non-exotic, local materials. We shall see.