A buyers guide to handmade functional pottery
I am a potter who makes functional handmade pottery. There are certain FAQ's I get asked by the general public at my market stalls and I thought a buyers guide that answered those questions might be useful. I want to give you the tools to recognise certain types of pottery and allow you to have a meaningful exchange with the craftsperson/salesperson/gallery owner you are thinking of buying from.
What type of pottery is it?
Pottery is a ceramic material (fired clay). It comes in a range of types and styles defined primarily by the type of clay used, the firing temperature, the type of kiln fuel and atmosphere, type of decoration method and the forming method. I will not go into extreme detail with all this here, as to do so would require a book and I want to keep this simple and avoid technical complexities.
Basically, if you keep in mind that high firing temperature equates to strength, hardness, non-porosity, and durability while low firing temperature equates to bright colours but weaker strength and porosity, you will have the general idea.
What type of clay and firing temperature?
Porcelain - There are two types - 'hard paste' porcelain fired to very high temperatures of about 1350-1400Celcius the highest firing temperatures of all pottery, and 'soft paste' porcelain fired to temperatures of about 1200Celcius. The high firing creates a material which is very 'glassy' and completely vitrified (non porous - does not absorb water, even without a glaze). This is a very strong material and therefore pottery can be made with very thin walls. If fired to its maturation temperature and if the ware is made thin enough, it will be translucent if held in front of a light source. It should give a clear ring if tapped with the fingernail. If it doesn't ring clearly, it may have a hidden crack (a flaw), or 'crazing' in the glaze (a fine or broad network of surface cracks in the glaze, also called 'crackle', which is not a flaw if used as a decorative effect) or was not fired to its maturation temperature (has not completely vitrified - may or may not be a flaw depending on the intentions of the potter). In its normal state, porcelain is very white (look at the unglazed area on the foot) but don't use whiteness in itself to identify it, as some of the other pottery I am going to talk about can also be white. White porcelain can also have colorants added to it to give all sorts of other colours. Porcelain clay is the most expensive clay for the potter and so the finished product will normally be more expensive than the other types of pottery. It is also a challenge to throw thinly on the potters wheel and can collapse in the kiln, so the expense also reflects these high level skills exercised by the potter.
Bone China - This is similar in its fine qualities to porcelain and was in fact developed in Europe in an attempt to compete with imported chinese porcelains of the time. It has the translucency and strength of porcelain but reaches maturation (non porous vitrification) at a lower temperature in the kiln. It is unusual in that the glaze firing (at about 1080Celcius) is lower than the first or 'bisque' firing (at about 1280Celcius). It is usually a creamy off-white colour.
Stoneware - This is a very commonly used clay as it is not as expensive as porcelain, is easier to work with and yet still fires to become a non-porous and strong kind of pottery. It is the second highest fired type of pottery after hard paste porcelain and is fired to anywhere between 1250 - 1300Celcius. It is usually a grey or brownish colour (actually like 'stone', hence the name), often with visible flecks of other materials within the clay (look at the unglazed foot) but can also be quite white and uniform (although not usually as pure white as porcelain). In fact, my material of choice at DM Pottery is a very white fine stoneware. The difference to porcelain is it will never be translucent, no matter how thin it is made. The walls of pots are usually left a little thicker than porcelain. It is a robust and useful material very suited to functional pottery for everyday use.
Mid-Fired Pottery - Many potters decide to fire their pottery in a temperature range that is between stoneware and earthenware. Temperatures range from about 1200 - 1250Celcius. This allows potters to create a harder and more durable product than earthenware but save on fuel/electricity costs by not having to go as hot as stoneware. It is becoming more popular as potters try to be more economically and environmentally sound. Some mid-fired pottery may be porous while others are non-porous (vitrified like stoneware) - it depends on the clay and the firing temperature within the mid-fire range.
Earthenware - This is a low fired pottery type and is porous (can absorb water) on its unglazed surfaces. It is fired to anywhere between 1000 -1120Celcius. It will give a dull clunk when tapped with your fingernail. The glazed surfaces will often have 'crazing' or 'crackle' (a network of surface cracks in the glaze), either evident on new wares due to a glaze/clay thermal expansion misfit, or develop on older wares because the clay body has absorbed water and 'swollen' over time, cracking the glaze which cannot expand in the same way. Often this crazing is a desired feature of the ware and should not always be considered a flaw, however, keep in mind that crazed areas on surfaces that come into contact with food can stain and even be a microbe hazard (although it never bothers me personally - and it is said an aged earthenware teapot makes the best tea). Earthenware usually comes in warm tones of brown, and for this pleasant colour it is often a potters first choice. It can also be white, so like I have already said, never use only the colour to determine the pottery type. Earthenware glazes are usually brighter and more saturated with colour than other types of wares because the low firing helps retain the vibrancy of the colouring oxides. A couple of distinctive styles of pottery that are types of earthenware are majolica (brushwork over a white tin glaze) and slipware (coloured liquid clays applied in various ways over the clay surface) .
Terracotta - This is really just a type of earthenware. It deserves its own category though because of its very distinctive colour ranging from burnt reds to bright oranges. It is the pottery that garden planters are made of, but can sometimes be found made into such things as robust cooking pots.
Raku - Again, really just another type of earthenware, but this kind of pottery has a very distinctive firing process and is fired to an even lower temperature (about 1000Celcius) than the average earthenware. It is removed from the kiln while the glaze is still molten and quickly cooled and usually put into a 'reduction bin' (an enclosed space with combustable materials which chemically removes some oxygen atoms from the ware). The unglazed surfaces are usually black or nearly so, and the glaze will usually have crazing, here definitely used to decorative effect as the cracks will have gone black like the underlying clay and stand out clearly and beautifully. The glaze colours are usually bright and sometimes lustrous. The clay must be resistant to thermal shock due to this firing process and is therefore very course grained which helps with this. Usually wares are decorative only, due to the porous and weak quality of the fired material, but traditionally in Japan it was and is used for vessels for the tea ceremony and is used throughout the world today for functional pottery as well. Not recommended for everyday items though, as they will become chipped easily.
Pit firing /saw-dust firing / Smoking - There are some firing techniques that involve relatively low temperatures, often without conventional kilns. A fire over a hole in the ground, or a bin full of slow burning saw-dust are examples. Glazes are rarely employed as the temperatures don't get hot enough to melt them and the wares produced, although often very beautiful, are fragile and porous and should be for decoration rather than for serving and eating food.
What type of kiln fuel and atmosphere?
The type of kiln fuel/power source effects the atmosphere inside the kiln which in turn effects the colour and other characteristics of the glaze on the pottery.
Reduction atmosphere - Anything that burns with a flame, such as gas, wood or oil makes it possible to have a reduction atmosphere in the kiln. 'Reduction' means the atmosphere in the kiln is starved of oxygen. The flame is so desperate for oxygen, it takes atoms from the glaze itself, changing the colour of some. A typical example of this is a copper red glaze. It is only red in a reduction firing. It is green in oxidation!
Oxidation atmosphere - Oxidation is where the kiln atmosphere has plenty of free oxygen present. Electric kilns have oxidation atmospheres.
Soda/salt atmosphere - This produces a distinctive type of pottery. The glaze is formed in the kiln by adding soda bicarbonate or salt to the hot kiln. It vaporises, moves through the kiln with the flames and settles on the pottery forming a special glaze. Colours are typically oranges or blues and greens and you will often see an 'orange peel' dimpled surface on the glaze.
Wood fired atmosphere - A wood burning kiln has a lot of ash from the wood flying through the kiln with the flames. This ash settles on the pottery, forming a distinctive glaze that pools and runs as it flows over the pots. Where the pottery does not get covered with ash glaze, the bare clay gets 'flashing' marks - beautiful orange and red marks where the clay has been in contact with flames.
What type of forming method?
It is nice to know how the pottery was made. The three broad categories are 1. wheel thrown, 2. slip cast, 3. hand built (from coils, slabs, pinched).
Wheel thrown - often has visible throwing rings and a symmetrical form (but not always). Throwing rings are the lines left by the potters fingers while they were shaping the form and are a lovely reminder that the pottery was handmade. Usually the walls are thicker at the bottom and thinner at the top, although a well thrown form will minimise this.
Slip cast - made with liquid clay in a plaster mould. This is still considered 'handmade' pottery if the work is not produced on a massive scale and the subsequent stages of production are done by hand, particularly the decoration. The original form from which the mould was made could have been designed and made by the potter also (but not necessarily). When it comes out of the mould there are seams where the parts of the mould meet. These seams are cut away, but if the wares aren't carefully made, the seams (or the cutting marks) may still be visible. Slip cast wares will usually be lighter and thinner than thrown pots and have a rounded quality to edges and changes in direction on the form.
Handbuilt (coil, slab or pinch) - often organic or non-symmetrical shapes that would be otherwise difficult to make on the wheel. Walls can vary greatly in thickness and evenness.
Sometimes more than one method can be employed on the one piece. For example, I sometimes use slabs (a kind of hand building technique) which I later add to a thrown base and continue to then throw on my wheel.
There are other forming methods like Ram-pressed, or Jigger Jolly (funny name I know) but they are getting away from what can be called 'handmade'. These methods have been utilised occasionally by studio potters to make unique work but I will not mention them here.
What kind of pottery is this? You now have the information to get close to determining this for yourself, just by doing a few simple checks. Look at the colour of the clay at the unglazed areas of the pot, look at the qualities of the glaze, tap the ware with your fingers to see if it rings (porcelain) or clunks (earthenware) or is somewhere in-between (stoneware), hold it up to the light to see if it is translucent (porcelain), and check if it is porous or not. How do you check whether it is porous? Well I probably shouldn't advise this unless you have already bought the piece, but you can test porosity by touching your tongue to the bare clay - if it sticks slightly it is porous.
Is this pottery microwave safe? This is probably the most commonly asked question of all but people can mean different things by it. Will this pottery crack in the microwave? Will it explode? Will the glaze leach chemicals? Will it get super hot? Will the decoration 'spark'. Ask the potter/salesperson if it is important to you, but remember, most potters are running a very small business and can't afford to get a lab to run extensive tests on this sort of thing.
Any pottery that is non-porous (porcelain, bone china, stoneware) should be safe as far as cracking or exploding goes. If porous pottery that has absorbed water goes into a microwave, the quick heating does not always give the water enough time to escape before it expands as steam and it is forced to crack or explode its way out from the pottery, so any porous pottery (earthenware, terracotta, raku) should definitely not go in a microwave.
Naturally, all pots get hot in a microwave as their food contents are getting hot and the heat gets transmitted through the ware. However, some glaze types seem to get much hotter then the food would dictate, and even handles away from food can get dangerously hot. Glazes high in iron seem to do this most commonly. It is helpful if the potter has tested for this and can advise you at the point of sale, but it is easy enough to test this for yourself when you get home with your pot. As an example, lets use a mug. Put your new mug in the microwave completely empty. Put another mug with water in it next to it (but not touching it). Microwave for 10 seconds and then carefully touch your new purchase. Has it started to get warm? Continue at 10 second intervals. If your new mug gets too hot to touch before the water in the other mug has boiled, then it is a problem glaze. Its not the end of the world though - just remember to always be careful and use an oven mitt with that pottery.
Any pottery that has been decorated with lustres - like gold or silver banding on the rim for example, must not go in the microwave. Like all metallic objects, it will spark and damage the microwave.
Is this pottery food safe? Generally, the most important issue that needs to be addressed here is whether there are any chemicals in the glaze that can leach into food. Lead and Barium are the main baddies. Preferably you want the potter to tell you that the glazes on their functional wares don't have either in them. As a potter, I am very careful not to have either material in my functional glazes. If these materials are present, then ideally, the potter should have had their wares tested at a lab for solubility of these materials. However, as I mentioned before, this is often not economically viable for a small-scale business. Safer then, that they are not present at all.
Ideally a food safe glaze shouldn't craze (mentioned earlier - fine cracks in the glaze). At a microscopic level, the cracks could hold food particles or microbes that could contaminate later servings in that pot. Personally, I have never heard of anybody getting sick in this way and a bit of crazing on my food pots doesn't really bother me. Having said that, I try to eliminate crazing from all of my glazes so that it isn't an issue.
Staining and cutlery marking can be a problem, most often on satin and matt glazes and on unglazed clay. For these reasons, ask the potter if they have checked for these problems if they are presenting these kinds of surfaces as food safe. Glossy glazes are far less likely to suffer from these problems, so look for gloss on surfaces that come into contact with food or cutlery.
Is this pottery dishwasher safe? A Japanese potter once told me that it is a mark of disrespect to the pot to put it in a dishwasher. The pot should be such a joy to handle, even in the cleaning, that the owner should want to clean it by hand. However, we live in a modern world and one must be realistic, right? The two dangers in the dishwasher are the force of the jets of water and the abrasion of some dishwashing detergents. In general, non porous, glazed, high fired pottery is safe, and porous, low fired, weak, unglazed pottery or pottery with decoration on the top of the fired glaze is not safe. Really thin-walled delicate porcelain may be risky, raku a definite no no. The safest is stoneware since it is high fired and strong like porcelain but usually has thicker walls and so is more robust.
A small selection of my stoneware pottery has some unglazed areas. I have tested this through 50 cycles of a dishwasher and the unglazed areas had smoothed slightly (actually became more pleasant to the touch). Over time this unglazed surface would probably suffer, so for these wares, I recommend to my customers that they hand wash.
Can this pottery go in the oven? No matter what people tell you, all handmade pottery is vulnerable to thermal shock (sudden temperature change). Some pottery types can withstand it better than others, but one must aways be careful. No pottery should ever be taken from the fridge and put directly into a hot oven - it will crack. Many stonewares are formulated to have high thermal shock resistance and are designed for making ovenware's. Most traditional cooking pots are earthenware but rely on a very gradual heating cycle. Raku by nature has high thermal shock resistance, but even still, care should be taken to heat gradually.
My stoneware products have been used under a grill and in the oven, but they are put in when the grill/oven is off, then heated slowly. Mugs and teapots get boiling water poured into them with no problems.
Will this spout pour well? A very tricky question and a challenge for all potters. There are many factors that influence whether a spout pours well and every potter will have a different theory about what makes one pour well and another pour badly. Pottery differs from a material like metal in that it tends to have a rounded edge at the rim rather than a really thin cutting edge. This means it is difficult to prevent the liquid from 'rolling around' the edge and dribbling down the outside of the pot. Things to look out for that contribute to a good pouring spout are; a long straight spout rather than a short curving spout, a spout that has a wide base and a small opening (puts the liquid under pressure and 'shoots' it out firmly), a spout that has a low point on the bottom edge of the opening designed to hold the inevitable drip and prevent it travelling down the outside of the pot, and as thin an edge as possible for clay - best achieved with porcelain. Ask the potter if you can test the pot with some water before you buy to be sure, as it really is quite a fickle thing.
If you are buying pottery at a venue where you can talk directly to the potter, than feel free to ask them any questions you have regarding their work. Most potters LOVE to talk about their pottery and will get a real sense of satisfaction from talking to someone who is interested and better still a little bit informed (like you are now after reading this). Gallery owners and other retail salespeople should be almost if not equally as informed about the work they are selling, so never be afraid to ask.
Remember, most potters value the work that they do and want their creations to retain their integrity as long as possible and perform their intended task as well as possible, so they will be honest with you when asked questions about their wares. If you feel that you are getting the answer they think you want to hear, then you might be talking to that rare person who just wants to make a quick sale, so use your common sense and the information I have given you here to make informed choices.
If you are interested in knowing more about me and my pottery, my website is www.dmpottery.com.au
My online shop is located at www.dmpottery.etsy.com