Clay (from the Greek “arguilos”: white clay), is the basic material of art, and of ceramics in particular, being one of the oldest materials used by man.
It can be used as a “vehicle” or as an “end” in itself, that is, it can be used to obtain molds, as a support to work with other materials, or it can be used as a definitive material and in this case it must be fired.
The clay is made up of particles of hydrated aluminum silicates, usually have a layered structure. It presents diverse colorations according to the impurities that it contains, being white once cooked when it is pure (in humid state they are usually gray). It arises from the decomposition of rocks containing feldspar, originated in a natural process that lasts tens of thousands of years.
Physically it is considered a colloid, with extremely small particles and a smooth surface. The diameter of the clay particles is less than 0.002 mm. In the clay textural fraction there can be nonmineral particles, the phytolites. Chemically it is a hydrated alumina silicate, whose formula is:
Al2O3 – 2SiO2 – H2O
It is characterized by acquiring plasticity when mixed with water, and also sonority and hardness when heated above 800°C. Clay hardened by the action of fire was the first ceramic made by man, and is still one of the cheapest and most widely used materials. Bricks, kitchen utensils, art objects and even musical instruments such as ocarina are made from clay. It is also used in many industrial processes, such as papermaking, cement production and chemical processes.
The clays can be classified according to the geological process that originated them and the location of the deposit in which they are found. It can be recognized:
Primary clay: this denomination is used when the deposit where it is found is the same place where it originated. Kaolin is the only known primary clay.
Secondary clays: are those that have been displaced after their formation, by physical or chemical forces. These include secondary kaolin, refractory clay, ball clay, surface clay and stoneware.
Clay has plastic properties, which means that when moistened it can be easily shaped. As it dries it becomes firm and when it is subjected to high temperatures chemical reactions occur which, among other changes, cause the clay to become a permanently rigid material, called ceramic.
Because of these properties the clay is used to make pottery objects, of practical and decorative use. The different types of clay, when mixed with different minerals and under various conditions, are used to produce earthenware, stoneware and porcelain. Depending on the mineral content of the soil, clay can appear in various colors, from a pale gray to a dark orange-red. A kiln designed specifically for firing clay is called a potter’s kiln.
Mankind discovered the useful properties of clay in prehistoric times, and one of the oldest vessels discovered is the clay pot. It was also used, since prehistoric times, to construct buildings, made of tapial, adobe and later brick, a construction element whose use still endures. Clay was also used in ancient times as a writing support. Thousands of years BC cuneiform writing was inscribed on clay tablets.
Fire-baked clay, ceramics, is one of the cheapest means of producing everyday objects, and one of the raw materials used profusely, even today. Bricks, vessels, plates, art objects, and even sarcophagi or musical instruments, such as ocarina, were modeled with clay. Clay is also used in many industrial processes, such as cement production, papermaking, and obtaining filtering substances.
Archaeologists use the magnetic characteristics of the fired clay, or transformed into a ceramic product, to date the clay elements that have remained with the same orientation and compare them with other historical periods, in bonfire bases, kilns, etc.
Selection of the clay, it is advisable to discard the surface layer. In some situations it is normal to have to grind.
In oriental cultures, it is normal to add one more step, which is to age these clays already made, from one generation to another.
The specific property of a clay is its plasticity. This property to that the water acts like lubricant facilitating the sliding of some particles on others when an effort is exerted. To determine it there is a very fast form. A sample of clay is taken, it is milled dry and water is added until it can be kneaded without sticking to the hands (plastic limit), once this in these conditions a bar or plate is made, either by hand (colombin) or by means of a manual extruder, it is weighed and some notches are marked at 10 cm exactly. It is left to dry to a constant weight and then measured again to check the contraction and to weigh it to see how much water we have managed to knead it with. The contraction will indicate the degree of plasticity, since the more plastic a clay is, the greater its drying contraction. For this measure to be effective, it must be compared with a standard sample we are already using.
In the case of a colombine, a circle is made, and we can see how it behaves when it dries, if it presents cracks… etc, it is really the initial, quick and practical test.
The basis of the method is based on the fact that the sands that accompany the clays as impurities retain the contraction, while pure clays have a very high contraction. This phenomenon is explained because the clays are flat particle and water conductive, while the sands are polyhedral particle and are not water conductive.
By Testing and Analysis of Clays, we understand all the tests and procedures used to know The nature of the surface clays, which most of the craftsmen use. The clays are so varied and rich in elements that their analysis and formal study are a true specialty.
The analysis of the plasticity, is totally practical and visual, a colombin is made, and we make a ring, seeing the shouts or fissures that come out, and as it has left us the sample when making the mud or with a plate in which marks are made to 10 cm. and we check the contraction and the difference in weight that we have in comparison with the obtained one in the mixture of the clay in dust, amount of water that it loses.
To analyze a clay you can always start from Pettijohn’s (1977) mineralogical classification, which begins with the classification of the material passed through meshes to obtain its granulometry, by retained, as well as the classification of these until arriving to what we are really interested in, the fine part that we could classify as clay in a natural way (mesh + of 200) this base material, or matrix, we decompose it for its study in three vectors to represent in a triaxial diagram:
a.-on the one hand the sands (silica feldspar, fine rock, mica, ect…)
b.- on the other side the organic matter (hummus, humic acid, and fulvic acids and finally
c.-minerals with true clay characteristics.
Once we have separated a determined quantity of (base material), we dissolve it from 100 to 200% with water and from 20 to 50 gr. of exametaphosphate of sodium by kg. in dry base.
We let it mature for 24 hours and then we add 25 gr (per kg, dry base) of caustic soda in flakes and we heat from 90 to 100 ° the material for at least one hour, already removed from the fire and fresh we add 100 gr. of sodium metasilicate, or its equivalent of silicate solution with constant agitation, we let it mature for 24 hours away from sunlight and filter through 350 mesh or more to separate the pure clay . ( the type and mineralogical quality is determined in another procedure from this point).
The rejected by the fine mesh is a mixture of hummus (humine) and fine mineral annexes (…. by calcination and difference of weight the percentage is extracted the dark liquor that accompanies to argillaceous part is carrier of the lignitic acid and the fulvic acid when decanting it this liquor is mixed with a solution of ethanol (alcohol of cane) 60% or more and forms a precipitate of first, that separates in a paper filter, remaining in the liquor single the fulvic acid.
The truth is that in many laboratories only the base material is separated, as in the beginning by examining the phosphate – sosa-silicate – meta-silicate, one part and another part directly by calcination to give “organic matter” … so much”, sands so much” and clay material so much”.
At first, with the calcination we can see the organic content by loss, at a temperature of 150 ºC more or less, during a certain time, the difference in weight, will be what marks us the quantity.
Other types of substances such as CaCO3 and MgCO3 over 800 ºC.
As for the fusing of clays, to give an example, a thin layer on a stoneware, and at different temperatures can identify us something the type of material, if it is fused, we will make a glaze at high temperature, (coffee with milk).
It can be observed with optical means and polarized samples of a clay, and composition.
Determine the lime content
Notes of the post Clays
I quote from claud Vitel in “Ceramics, pastes and glazes, page 33:
In a glass, add 5 g of clay, previously crushed and dried, after diluting it with a little water. Add diluted hydrochloric acid, weigh the whole, and pour the acid into the glass. After about ten minutes, when the effervescence is over, everything is weighed again.
The decrease in weight indicates the loss of carbon dioxide gas, which will make it possible to determine the content of the clay in calcium carbonate.
100g of CaCO3 = 56 g CaO + 44 g CO2
You can try as a guide, to use vinegar… Or whatever you have at hand, good luck.
That the commercial murriatic acid is a solution to 30 or 35% of HC and the ecc, is like this
100.08g CaCO3 + (72.92g pure) 2(HCl)= 110.99g Ca Cl2 + 44g CO2 +18g H2O
In practical terms 1 gr. carbonates produces 0.44 gr, of carbonic gas and for that it is required to add at least 2.2 gr of commercial acid to the mixture.
1 gram of carbonates still produces 0.44 of carbon dioxide gas, but since cane vinegar comes in 5%, it will be necessary to add at least 24 grams of vinegar for each point. (and heat).
I love polymer clay, it’s so versatile that, from the heart, I think it’s impossible to get tired or stop learning things from it! and fortunately it is more and more known and there are more people interested in using it… but of course, then one starts to investigate and gets lost in the maelstrom of brands, tools and materials, and doesn’t know very well where to throw it; So, as I have already gone through it, after the introductory article “Starting with polymer clay”, I think the next question to be answered is what basic tools do I need to start (and not ruin myself in the attempt)?
If you want to work comfortably, and without staining, the first thing you need is a non-porous work surface. However, as you can imagine, it has to be one of those with a completely smooth surface, those with squares or flowers in relief are not worth it… in fact, I would say that the best thing is for it to be white and that it does not have any kind of drawing, not even flat, because this way you can focus much better on what you are doing without the interference that the shapes and colors of the tile can introduce. I was lucky and in the last place I lived we had at our disposal the leftover tiles from the bathrooms, which turned out to be perfect for this, so I had it easy!
If you find it impossible to get a tile, don’t despair, remember that the only important thing is that it be a smooth and non-porous surface, so there are many options! How about those kitchen cutting boards that are made of glass, for example? I have one (turquoise color), which I use when I go to courses because it is smaller and lighter than the tile. These boards are cheap, very resistant, and also, as they have become fashionable, are usually very easy to find. And already put to use glass … why not go for example to a glassmaker and ask one of the measure you want? well, surely if you think you can think of many more cheap options, the important thing is that your work surface is not porous material, like wood, because the clay will be stuck, and then you will find it impossible to clean it.
It seems pretty obvious, but don’t lose sight of the fact that polymer clay, as we already saw, needs to be baked to harden, so before you consider working with this material make sure you have access to a kiln.
Nowadays almost everyone has an oven in their kitchen, and that is usually more than enough to get the 110ºC to 150ºC range needed for polymer clay (depending on the brand). I also told you that the clay, baked at its normal temperature, is not toxic, so in principle there is no problem in using the same oven as for the food, as long as you don’t put it in at the same time as your pieces, and air it out a bit. Even so, you may get bad vibrations, or find it uncomfortable to have to go back and forth from the kitchen with the pieces, or you may find it hard to be conscious of turning on such a big oven to bake small pieces, because of the energy it takes. In that case, you can always get a smaller oven, which you can put in any room of the house and use only for non-food use. That’s what I did. As soon as I decided that I needed an oven for my pieces I kept my eyes wide open… until I found a good offer for a small electric oven, which was very cheap and is the one I’ve been using ever since! The important thing is that it has temperature control, and that it applies heat evenly.
More than one will roll their eyes when they see that I have put the laminator on my must-have list, I know, there are people who even after quite some time continue to work without a laminator… but for me it doesn’t make any sense: if I don’t have a laminator, I don’t even think about getting into clay.
It is a basic tool, for example, to condition the clay. Because it turns out that you can’t use it as it comes out of the package, no, you have to knead it and soften it in order to work with it, just like we did with clay when we were little. And just as with the clay, the polymer clay is a little hard when it is taken out of the package, so kneading it with your hands can become a mission impossible. I don’t know how you did it, but I remember putting the plasticine on top of the radiators so that it would soften a little with the heat and then we could do something… that was because we didn’t know about the laminators, a divine invention! All you have to do is cut the clay into not very thick pieces, pass them through the laminator a few times and you are ready to work! Not to mention how useful it is to make sheets of clay of uniform thickness with the minimum effort (basic for many techniques), and to apply some textures, make gradients, mixtures… it is one of those tools that makes your life easier.
Its detractors will tell you that it is an expensive tool, that you can start without it and even buy it if you see that you like it… and I always answer to that:
It’s not that expensive. There are many brands, and obviously the most resistant and recommended do rise a bit (we are talking about 40 euros), but if that price throws you back for sure you find some more cheap with which to start. You just have to keep your eyes wide open: decoration stores (in the kitchenware part), white brands from craft stores, bazaars… Then when you see how useful it is, I’m sure you end up buying one of the good ones.
If you don’t have a laminator there is a much greater chance that you will decide that you don’t like to work with polymer clay and you will end up leaving it. I have already seen more than one case, people who condition the clay by hand and end up having stress tendinitis, and then there are many techniques that they cannot apply, so they cannot get all the potential out of it… and they decide that it does not convince them. I assure you, with a tooooood laminator it is much easier to put a laminator in your life!
There are many types: rigid, flexible, corrugated, large, small … to begin with, the completely essential is the rigid blade, and at most, the flexible.
It’s funny to me because blades are tools that we clay makers seem to like to collect. You start with one, or two, and over time you get a whole arsenal. We have the “I buy a new one because it doesn’t cut well anymore, but there are things it’s still good for so I don’t throw it away”, or also the “My blade! Where is my blade? I’m going to buy a new one because I can’t live without it (and of course it shows up later)”, and let’s not forget the “My blade broke in half, how cool, because I missed having a smaller one! But now I need another big one…”.
The fact is that some people will also tell you that on the first day you don’t need to invest in blades, that you can get by with a cutter of the usual kind, error! Obviously a cutter can get you out of a hurry (and it’s good to know how to adapt to the circumstances if that’s the case), but because of its shape, it doesn’t allow you to do many of the things you would do with a clay blade comfortably, and if you take off the handle to use it for its full length… well, honestly, the cutter is not designed to be used like that and it’s dangerous, apart from the fact that it’s still much more uncomfortable than using a clay blade in proper conditions. Seriously, do not skimp on this, buy at least a special rigid blade for clay, simple, there are some very well priced and your hands will appreciate it.
Another one of those tools that doesn’t seem to be indispensable at first… but believe me, having it will avoid you many annoyances and headaches.
Polymer clay can be very frightening when it comes to baking temperature: if you fall short, the piece will not heal well and will be fragile and brittle, and if you overdo it… well, let’s just say that polymer clay charcoal is not good for barbecues and it’s also toxic! Of course there is a margin of a few degrees up or down that you can work, but it’s not too wide either, so knowing the exact temperature you’re baking your pieces at is pretty essential to having good results.
And you’ll tell me, but doesn’t the oven already set the temperature? Isn’t it enough to set the knob at 130ºC to make sure there’s actually 130ºC inside? Well, no! And all for a simple reason: ovens are designed to heat food, and food is not as sensitive to temperature changes as polymer clay. I don’t need great precision to make a pizza… it could work at any temperature between 150ºC and 180ºC, and I don’t need the oven temperature to be perfect and constant throughout the baking time, because the pizza will hardly notice the ups and downs. So what happens? Well, the oven temperature controllers leave a lot to be desired in this respect. They are more than sufficient for the food, which is their mission, but not for the clay.
The solution is to have a kiln thermometer and to put it inside during the preheating, so that we can see before putting our pieces in if the temperature marked by the kiln corresponds to reality, and if not, readjust it and bake without frights! I sincerely believe that what I have gained in tranquility and control since I have the thermometer is priceless, and on top of that it turns out that it is not an expensive utensil. Like everything else, there are some that go up a bit more in price, but if you look hard enough you can surely find one at a reasonable price. And remember that it’s just an oven thermometer… apart from the craft stores, you can look in kitchenware stores!
Yes, another one of those tools that almost nobody would put on their must-have list, I don’t understand why!
People when they start, NEVER buy the drill, including me. You do your best, making holes in the pieces before baking them with a punch, a thick needle… and the pieces get deformed. Seriously, it doesn’t matter how you do it or how much effort you put in, the pieces deform, because they are soft, and you squeeze on one side, squeeze on the other… and they get squeezed. It’s absolutely inevitable.
So one day you see someone with a drill, and you decide to try it, and you fall in love! And suddenly with the drill you see that you can make the holes in the pieces after baking them, without difficulty, without deformation, in ways that you would never have thought of before… and a door opens for you that you didn’t even know existed, and assembly possibilities that you would never have thought of in life. Once you have the drill, you can no longer live without it, and you only have to ask yourself “why didn’t I buy it before”, so don’t think about it anymore, buy it from the beginning!
But the best part of it all is that, if you don’t want to spend too much at first, we also have a low cost option! You can go to a do-it-yourself store and buy a loose 2mm drill bit, which is what you will use the most, or even a complete set of drills, from the cheap mallets (sometimes a set costs even less than a loose drill bit). For 2 or 3 euros you get it. And then you go home, make a roller with some clay, prick the drill and put it in the oven, you have your drill with a handle, so you can use it comfortably!
It is not that it is the best tool in the world, I recommend that in time you buy the hand drill anyway, but to get out of the way it is more than enough, and believe me, you will be grateful to infinity.
That yes, nobody likes sanding, and this seems something super optional … you’ll see, but of course if you want a good finish for your pieces, sanding is the only way.
No matter how well you work, no matter how clean and careful you are, no matter how much you smooth the surface before baking, the reality is that you will never manage to leave a piece completely free of imperfections. And at first you don’t notice it, I assure you, you are so happy with your pieces that you don’t even think they could be better, but the truth is that they could be, and in a very easy way too! You only need a couple of sheets of waterproof sandpaper, sold in hardware and do-it-yourself stores, of grain 240, 400 and 1000 (approximately, take these values only as a reference).
Take a bowl or a small barreñito and put water and some drops of dishwasher.
Cut a small piece of the thickest sandpaper, the 240 grain, wet it, and wet your piece already baked.
With patience, sand the entire surface of the piece regularly, making sure it is smooth and soft. This thick sandpaper is the one you have to use to eliminate all the imperfections, prints, and to go over the edges…
When you finish with the 240 sandpaper, rinse your piece, and repeat the operation with the 400 sandpaper (always wet). So what we do is remove the marks or scratches that we may have caused with the previous coarse sandpaper.
Finally, go over it with the 1000 grit sandpaper… you’ll see how you’ll notice the difference afterwards, you haven’t touched anything so soft in your life!
And don’t forget to wash the piece well with water, soap and a little brush when you are done, to remove all the sanding remains and make it perfect!
With this simple (and inexpensive) process, you will see how the finish of your pieces improves substantially.
It is not easy to teach because the difference is more noticeable to the touch, but do you see the difference between the two petals on the right and the rest? If you could touch it you would be amazed…
You have to sand thoroughly with each sandpaper to eliminate all the scratches produced by the previous one and that the piece is very smooth and without marks… but if when you finish it you have left something whitish, add a little bit of Nivea cream (or some other, the more fat the better) and rub it well with a soft cotton cloth, you will see how it improves!
The surface finish will be matte, of course, because to get a shine you would have to keep on using more and more sandpapers, with finer and finer grain (have you heard of Micromesh sandpapers?) and finally polish, and you can leave all that for later, when you get hooked on the clay and decide to invest in more tools and materials. But to begin with, you’ll see that only with the 3 sandpapers I told you about and the light polishing with the cotton cloth the finish of your pieces already goes up a step.
I have already told you a thousand and one times that the best thing about clay is its versatility, and precisely because of the variety of techniques that can be carried out with it, there are also many tools that can help you. However, don’t go crazy, having the basics you can already do a lot, and if you learn to look at your house “with different eyes” you will see that there are many things you can give an alternative use to:
And that’s it for now! I hope that I have helped you and given you some ideas… above all, that money is not an impediment to start working with polymer clay! because at the beginning it is a bit scary, but going to the basics you can do many things, and for everything you can look for options.