|the paragon vulcan kiln||or tumblers at electrictumblers.co.uk|
The Paragon Vulcan Mobile kiln is generally used for melting and mixing glasses in a crucible, annealing, casting, and moulding glass, ceramics, porcelain, pottery, and raku, although it has other applications. It's a 1290°C kiln with a digital programmer, in Paragon black, or customised berry, blue, jade, navy, pink, purple, or turquoise. Learn about the Paragon Vulcan kiln on this page.
There's only one version: the Vulcan Mobile: a complete wheel-away kiln with a move-aside crucible cover on a pivot assembly. In the US, it's called the Vulcan ll.
Prices here are transparent: they're for UK-EU voltage, CE marked, CL CSA approved, and TUV tested kilns, and include comprehensive instructions, UK VAT, and free continuing support from a top-tier international distributor.
For prices, trading terms, and secure on-line shopping, use the shop link below the menu bar near the top-right of any page. The order form is on the shop page, after the price list near the bottom.
Kilns that weigh more than 30kg can't be delivered by a regular parcel-service van: they need a tail-lift lorry with a hydraulic pallet trolley. GB-mainland delivery charges are on the shop page. For other locations, call or mail.
|Paragon Vulcan Mobile Crucible Kiln.||Paragon Vulcan Mobile Crucible Kiln.|
|Paragon Vulcan Mobile Crucible Kiln.||Typical Crucible.|
|Paragon Sentry Digital Programmer.||Paragon Sentinel Touch-Screen Digital Controller.|
|A GENERAL INTRODUCTION TO THE PARAGON VULCAN KILN||OPTIONAL READING|
The Paragon Vulcan Mobile kiln is generally used for melting and mixing glasses in a crucible, annealing, casting, and moulding glass, ceramics, porcelain, pottery, and raku, although it has other applications.
Yours can be in Paragon blue or customised berry, black, jade, navy, pink, purple, or turquoise. However, it's only the control boxes that are painted: not the whole kiln. Customised kilns are made to order, so can't be returned if the colour isn't exactly as in the photo.
It normally has an enhanced Sentry 12-key programmer. Its features include thirty-five free-to-set sequences, each one with up to twenty segments, and automatic control over hardware options: an electric kiln vent, a gas injection system, and a USB computer interface.
Alternatively, you can choose an advanced touch-screen Sentinel Smart Touch. Features include those of the Sentry 12-key and real time displays of voltage and current, a novice mode with prompts, firing sequences presented graphically, and wifi updates: so a functional upgrade not just a design preference.
When the programmer turns the elements off at, for example, 700°C, residual heat will continue to increase the temperature briefly. A small kiln might overshoot to 715°C before dropping back down. The programmer's software slows down the heating just before the target temperature, reducing any overshoot and improving the accuracy.
Digital programmers allow you to set up sequences, each one with multiple heating, holding, or cooling segments: so you can choose the heating and cooling rates, target temperatures, and hold times, save the sequences, and re-use them.
Being able to create, edit, and save your own programmes is important because, having experimented and diversified, most people fire materials, or combinations of materials, at different temperatures and for different times than are recommended.
Most kilns, even those designed to run at 1290°C, use K23 bricks. These have excellent insulation and resist thermal shock. However, putting heavy crucibles in and out of a kiln is safer with K25 bricks. They're denser and stronger than K23, although take a little longer to heat up. To offset the time penalty, the firing chamber side walls are built from 114mm thick bricks, and the top and bottom from 76mm thick bricks.
Most kilns use a special-limit nickel-chromium K-type thermocouples. These respond quickly to changes in temperature, resist corrosion, and have an error margin of less than 0.4% instead of the typical 0.8%. However, for continual high-temperature high-precision professional use, the Vulcan uses a platinum-rhodium S-type.
The US-international kilns don't come with a shelf or posts or kiln wash or a crucible so, if you don't need these, you won't have to pay for them. However, I've recommended pro kits because a durable heavy cordierite shelf resists thermal fracture, provides a smooth stable work surface, protects the floor of the kiln's interior from glass accidents, and helps to even out any small temperature deviations during annealing, enamelling, firing, fusing, and heat treating as the elements turn on and off.
For help, or in the unlikely event of a fault, you can mail or call an engineer in the UK. However, checks, adjustments, and repairs are simple, needing little more than a PosiDriv screwdriver: watch the on-line videos using the watch-videos link or read the help pages using use the help link, both below the menu bar near the top of any page. Alternatively, we can service the kiln in our workshop at Cherry Heaven.
APPLICATIONS: WHAT CAN I DO WITH A PARAGON VULCAN KILN?
Use them for crucible glass work, firing ceramics, earthenware, porcelain, pottery, and stoneware, glass annealing, bisqueware, ceramic art, china painting, applying decals, doll making, fire polishing, glass art, glass fusing, sagging, and slumping, heat treating, laboratory testing, lampwork, lost-wax casting, mixing custom glass colours, pâte de verre, raku, staining glass, hardening and tempering blades, cutters, dies, and tools, and many other materials and processes.
You can make architectural features, bowls, ceramic art, chandeliers, decorations, figurines, glass-art, glass panels, glass stringers, knives, lampshades, mugs, ornaments, plates, stained-glass designs, tableware, tiaras, tiles, tools, and vases, as unique hand-crafted pieces or as repeatable stock for sale.
It's ideal for your arts centre, ceramics studio, college, course venue, craft classes, engineering works, glassworks, knife-making workshop, laboratory, machine shop, metalwork business, school, technical facility, or university.
IS A PARAGON VULCAN KILN THE BEST CHOICE?
The Vulcan ll kiln has been designed for crucible work. However, if you think that a larger, front-opener, or more specialised kiln might be more useful, here are some suggestions:
Bead-annealing kilns generally have a maximum temperature of 650°C. For these, look at the BlueBird. However, other kilns have bead doors: the small 1290°C Caldera B and 1095°C SC2B, the medium 1290°C Xpress E12B, and the larger 925°C Fusion 14B. These are all hotter than the BlueBird, so more versatile.
Glass kilns generally have a maximum temperature of 925°C. For these, look at the F Series, Fusion:CS Series, GL Series, or Pearl Series. These are not hot enough for ceramics and porcelain.
Jewellery, silver clay, and enamelling kilns generally have a maximum temperature of 1095°C. For these, look at the small SC Series or the medium Xpress Series. The SC series are not hot enough for ceramics and porcelain.
Vitrigraph kilns generally have a maximum temperature of 1095°C. For these, look at the small Caldera or the medium Vitrigraph.
Ceramics kilns generally have a maximum temperature of 1290°C. For these, look at the small Caldera Series and FireFly Series, medium Xpress Series, or large Janus Series, PMT Series, and TNF Series. These can also be used for glass work.
Heat-treating kilns generally have a maximum temperature of 1095°C or 1290°C. For these, look at the HT Series and PMT Series. Although they look similar, the HT has a bottom-hinged door and the PMT has a side-hinged door.
Knife-making kilns generally have a maximum temperature of 1290°C. The KM Series are made for depth rather than width. You can choose a guillotine, drop-down, or a side-hinged door.
The W Series have a top vent so are usually used for jewellery moulds and lost-wax burnout. For lost wax casting there are optional metal grids and wax trays. The small SC Series and most of the medium Xpress Series also have top vents.
To learn more about these and other kilns, use the appropriate links below the menu bar near the top of the page. And remember that each series has kilns of different sizes with different options.
|VERSION||DESCRIPTION||MAX °C||WATTS||WKG||INTERIOR||INTERIOR SIZE MM|
|Vulcan ll Mobile||top opening||1290||7000||197||firebrick||eight-sided 343 x 381|
|Caldera||top opening||1290||1800||20||firebrick||square 203 x 203 x 171|
|F130 Elite||front punty door||925||2400||79||firebrick||square 279 x 279 x 330|
|Fusion CS16D||lid and body opening||925||2400||85||firebrick||square 406 x 406 x 165|
|GL-22ADTSD||front opener||1095||11000||152||firebrick||square 533 x 533 x 337|
|HT22||front opening||1095 or 1290||7200||140||firebrick||square 533 x 533 x 337|
|Janus 1613||top opening||1290||4800||90||firebrick||eight-sided 419 x 337|
|KM24||front opening||1290||2600||63||firebrick||rectangular 140 x 610 x 108|
|Pearl 18||top opening||925||4000||115||firebrick||square 457 x 457 x 216|
|PMT21||front opening||1290||9600||290||firebrick||square 533 x 533 x 330|
|SC2||front opening||1095||1680||16||ceramic fibre||square 199 x 204 x 145|
|Xpress E12||front opening||1290||2700||38||firebrick||rectangular 196 x 295 x 219|
PARAGON VULCAN MOBILE
|CASTING, CERAMICS, CRUCIBLES, GLASS, PORCELAIN, POTTERY, AND RAKU|
The Paragon Vulcan Mobile is a 1290°C, eight-sided, top-opening, floor-standing, firebrick kiln, with a cone-fire ramp-hold, Sentry 12-key digital programmer. Choose Paragon black or customised blue, jade, navy, pink, purple, or turquoise.
The UK-EU kiln is rated at 230V-240V 7000W, so it needs a 30A minimum wired-in power supply. It's fitted with a switch that cuts off power to the elements when the kiln is opened: a legal safety requirement. However, never get careless: kilns are very hot and connected to the mains.
The external dimensions are 864mm x 711mm x 864mm high. The case has slots for air circulation, four lifting handles, and three lockable casters. The shipping weight, including the crate, is about 200Kg.
The firing chamber measures 343mm x 381mm high internally, and heats from the sides, with the heavy-duty elements in dropped recessed grooves in the 114mm thick K-25 bricks. The kiln normally has a quiet long-life mercury relay and a long-life S-type platinum-rhodium thermocouple.
The firebrick lid has a fold-away lockable support. The crucible hole in the lid has a 305mm diameter firebrick cover on pivoting support arms so you won't have to find a place to lay a hot cover. It moves up and out of the way with one-handed operation. The top and the crucible cover have stay-cool wooden handles.
The programmer's electronic display prompts for heating rates, target temperatures, and hold times, making it easy to set up and re-use accurate heating, holding, and cooling sequences. The cone-fire mode, up to cone 10, will simplify your work with ceramics.
The accessories, options, and upgrades for this kiln are in the on-line shop:
a berry, blue, jade, navy, pink, purple, or turquoise respray: normally black
a programmer upgrade from a Sentry Xpress 12-key to a Sentinel Touch: factory fitted
a gas injection flow meter with a controlling solenoid: factory fitted
an electric kiln vent: factory fitted at the bottom
an auxiliary power output for automatic vent control: factory fitted
a USB computer interface: factory fitted
stacking shelf kits and shelf paper
ceramic fibre cloth
HEPA dust mask
clear protective glasses
|EXTRACTS FROM REVIEWS, AND MY OPINION|
The Paragon Vulcan ll Mobile is a fully programmable, deluxe, professional-quality kiln for every kind of ceramic and glass work, so it's ideal for commercial studios. It's large enough to melt about 22kg of glass or hold four stacked shelves, yet it still heats up quickly. The Sentry 12-key programmer allows you to add automated gas injection, a controllable electric vent, and a USB computer interface.
The body is clipped to the base so, if a crucible cracks, the pieces will be easy to remove: if moulten glass leaks out, you'll only have to replace the floor. And, for extra practicality, the floor is reversible.
Most kilns use Kanthal A1 element wire. However, for continual high-temperature high-precision professional use, the Vulcan uses Kanthal APM. Kanthal APM has slow ageing and a low change in resistance over time. It has excellent surface oxide properties, which gives good protection in corrosive atmospheres as well as in atmospheres with high carbon potential, and no scaling. Although The kiln normally has these durable high-quality elements, the very long firing times mean that they're not guaranteed.
|PARAGON VULCAN ll MOBILE KILN FURNITURE|
There's a recommended kit, not included in the price: one durable round 254mm x 12mm cordierite shelf, three 12mm shelf posts, and 450gms of kiln wash.
There's an extra recommended kit, not included in the price: one round 254mm x 12mm shelf and three posts. You can choose 12mm, 25mm, 50mm, 75mm, or 100mm posts.
Depending on the material or process, and the sizes of your pieces, stacked shelves will hold more work, free up your time, and reduce the unit firing cost: so you might want more kits. This kiln has room for four.
Paragon says that the kiln will hold about 22kg of glass. However, as it no longer sells crucibles, there are some on line: just choose the right size.
The remaining sections are recommended reading, unless you're already using kilns successfully.
Cherry Heaven has been a Paragon distributor since 2002, and commended every year for outstanding performance. Paragon kilns are good value: buy Paragons and you could save enough to treat yourself to a luxury five-star weekend break.
Anyone can buy a kiln to resell and call themselves a specialist, but a top-tier distributor understands all the kilns, options, and upgrades, will stock spares, offers free competent technical support, can help you repair your kiln, provides on-line repair videos, has a repair workshop, and can access Paragon's extensive knowledge-base.
If you need help, you can mail an experienced technician or call . Alternatively, to learn more about how your kiln works, use the help link below the menu bar near the top of the page.
A BRIEF INTRODUCTION TO GLASS AND GEMS
The main component of glass is silicon dioxide, often called silica: found naturally and plentifully as sand. When it melts, at around 1700°C, it's like syrup on a cold day. When it cools, it forms a rigid brittle glass called quartz glass.
To lower the melting point, and reduce the cost of melting, chemicals are added: typically sodium carbonate and calcium oxide. Other chemicals, and different heating and cooling processes, produce a range of colours and mechanical properties.
Chemically, glass is defined as an amorphous solid but, as it's heated, it becomes softer allowing it to be blown, cast, coated, decorated, engraved, heat-treated, moulded, poured, pressed, sagged, and slumped.
A form of glass occurs naturally within the mouth of a volcano when the intense heat of an eruption melts sand to form Obsidian, a hard black-to-brown glassy type of stone, shown in the photo. Although it was used decoratively, when it fractures it has very sharp edges, many times sharper than a steel knife-edge, so was also used for tools and weapons: and the pitiful rituals of circumcision and female genital mutilation.
Very briefly, annealing generally involves heating glass or metal to it's annealing point, maintaining a specific temperature for a set time, and then cooling it to room temperature.
During annealing, fabrication stresses are relieved as the molecules cool and arrange themselves into a regular stable matrix. Successful annealing is the key to creating work that will remain attractive and durable. It can be quite a long process, and involve multiple phases, so a kiln with an automatic comprehensive programmer is essential.
|FREE BEAD ANNEALING GUIDE|
You can download, and print, a Bead Annealing Guide. Paragon created it in 2013 so it's only a guide, not a contemporary definitive document. Click here. It's a pdf file, but your device should already have a pdf viewer.
Glass scraps, with optional bubble powder, are put in a tray or a mould and heated. As the temperature increases the glasses begin to bubble. The bubbles mix the colours and give a natural organic appearance. The glasses need to be compatible as different colours and expansion coefficient might not work, so the boiled glass technique needs experiment and practice.
You increase the temperature at about 300°C per hour to 925°C with no bubble squeeze and soak for 10–15 minutes. Then allow the kiln to drop the temperature as fast as possible to about 815°C and soak there for around 30 minutes to allow the little bubbles to rise to the surface and burst. Then reduce to the annealing temperature and soak for the thickness you calculated in preparation for the firing.
Cubic Zirconia is the most popular substitute for a diamond because they look almost dentical. Cubic Zirconia or CZ, is made from zirconium dioxide which comes closer than any other gem to matching the characteristics of a diamond. It's not quite as hard as diamond and is slightly less sparkly but displays more prismatic fire with more colour sparkles within the gem, especially if metal oxides are added during the production process.
Caring for CZ is important because they are more brittle than diamonds and susceptible to wear and tear such as chipping and scratches over time.
A decal or transfer is an image or pattern printed on a ceramic, cloth, paper, or plastic substrate that can be moved on to another surface, usually with the aid of water and heat.
A wet decal can be slid into position, allowed to dry, and then heated in a kiln. Most ceramic decals come with a cone number for easy firing, typically cone 022. The programmer on the Paragon Fusion 7XL has pre-set cone numbers as well as the normal ramp-hold options used for general glass work.
Decals are a quick and fun way to decorate bottles, glasses, and vases, as most low-fire ceramic decals and low-fire glass decals will work very well, even on float glass.
Diamonds are not a form of glass: they're naturally occurring gems composed of carbon atoms arranged in a very regular pattern.
Between 1 billion to 3.3 billion years ago, simple carbon containing trace minerals was transformed into diamonds by heat and pressure at depths of over 100 miles below the earth’s surface. We can’t mine down far enough to reach the earth’s mantle but fortunately volcanic eruptions brought the diamonds closer to the surface. They're extremely hard and until recently were regarded as the world's hardest natural material.
Although diamonds are extremely expensive, their price is governed by carat, cut, colour, and clarity. It’s very rare to find a diamond that doesn’t contain flaws: however the impurities, and internal refraction and dispersion of light, give diamonds their brilliance.
Synthetic diamonds are manufactured and are identical in hardness, dispersion, gravity, refraction and chemical composition to the highest quality mined diamonds available. Whereas a one-carat top quality diamond would cost thousands of pounds to buy, the same quality man-made diamond could be made for less than £5.
This will obviously have a huge impact on the diamond industry over the next few years as when comparing a cultured and mined diamond side by side they are virtually undistinguishable. A bit like pearls, they can be grown from a single crystal using chemical vapor deposition.
Dichroic glass has two different colours: a transmitted colour and a reflective colour, both of which change depending on the angle of view. For example blue-red will be blue in transmission and red in reflection.
During manufacture, quartz and metal oxides are vapourised onto the surface of the glass using a vacuum deposition process, forming a multi-layer crystal structure.
Enamelling involves applying a glass paste to metal and then heating it to fuse it to the surface. The finish of the enamel can be translucent or opaque depending on the temperature used to melt the glass. Higher temperatures result in a more transparent and durable enamel whilst lower temperatures give a more opaque and fragile surface. Dyes and pigments can be included to produce any colour.
The Paragon SC2 is ideal for enamelling, although other kilns are fine. So click the sc2-sc3:jewellery link below the menu bar near the top of the page. The SC-2W and SC-3W doors include a 50mm x 50mm heat-resistant glass viewing-window in the centre of the door, allowing you to take a quick peep at china paints, enamels, glass, and glazes to check on their progress
To fire polish glass, return the items to the kiln and melt them just enough to give a smooth polished appearance. It needs a temperature of around 700°C, and is often used to round the edges of glass after fusing.
Fire polishing already-slumped items is more difficult because the polishing temperature is close to the slumping temperature and it can distort the appearance of the piece. So it generally works best for flat items, rather than slumped ones. It has the slight limitation that the part of the item that touches the kiln shelf won't polish.
|FUSING, SAGGING, AND SLUMPING|
If two or more pieces of glass in contact are heated, they begin to soften and fuse together. With careful heating and cooling, the separate pieces of glass become one.
If glass is put on a mould and heated, it begins to soften and collapse, or sag, onto the mould: a common technique for making bowls and plates.
Sagging and slumping are often thought of as being the same. Correctly: during sagging, heated glass, supported at its edges, sags down in the middle to conform to a mould; during slumping, heated glass, supported at its middle, slumps down at its edges to conform to a mould.
|LAMPWORK AND BEADS|
Lamp-working is the traditional name for glasswork that uses a flame to melt glass rods and tubes. As the glass softens, it's shaped by turning and using tools.
Early lampworkers used an oil-lamp, and blew air into the flame through a pipe. Later, propane, natural gas, or butane torches replaced the lamp, although kilns are now increasingly popular, particularly for annealing.
Beads are usually made on steel rods, or mandrels. When the beads are finished, the rods are removed leaving holes for threading the beads. Cold working techniques can be used, such as etching, faceting, polishing, and sandblasting.
Lost-wax burnout starts with making a wax shape and then making a mould of the shape. When the mould is heated in a kiln, the wax melts out through channels, usually over a burnout mesh and into a tray. The shape is then cast in glass or metal from the mould.
It's important to prevent wax or carbon sticking to the elements, so burnout kilns have a top vent to release fumes. Carbon build-up inside a kiln could conduct electricity and would eventually cause the elements to fail.
Paragon make kilns designed for this: the W series. So click the w:lost-wax link under the menu bar near the top of the page. They all have top vents and optional wax trays.
Moissanite is another diamond substitute which is a rare mineral found naturally in small quantities, although Moissanite for jewellery is artificially made. It’s made from Silicon Carbide which means it’s able to withstand high temperatures and is very hard.
Moissanite is noticeably much sparklier and displays more prismatic fire than a diamond which is noticeable even to an untrained observer. Moissanite does have inclusions like a diamond and it may also have a greenish tinge to its colour.
|PÂTE DE VERRE|
Pâte de verre involves making a glass paste, applying it to a mould, firing it, and removing the piece from the mould. The glass paste is usually made from glass powder, a binder such as gum arabic, distilled water, and colouring agents or enamels. It allows precise placing of colours in the mould, whereas other techniques often result in the glass straying from its intended position.
I think, currently, Daum is the only large commercial crystal manufacturer using the pâte de verre process for art glass and crystal sculptures.
This a simple technique but it requires good ideas. A bottle, such as those used for wine, beer, cola, or champagne, is softened in a kiln so that it begins to flatten out or conforms to a mould. There are too many moulds to stock here but there are lots available on line. Or make your own from clay.
The bottles need to be clean and dry, with all paper labels and tops removed. Put them in your kiln on a shelf, either with shelf paper or kiln wash to prevent the glass sticking to the shelf.
Paragon makes a kiln designed for this: the Trio. So click the trio link below the menu bar near the top of the page. It's wide enough for most bottles but can still use a regular socket.
Stained glass is glass that has been coloured by adding metallic salts during its manufacture. The coloured glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures, traditionally held together by strips of lead and supported by a rigid frame. Painted details and yellow stain are often used to enhance the design.
The term stained glass is also applied to windows in which the colours have been painted onto the glass and then fused to the glass in a kiln.
It requires artistic skill to conceive an appropriate and workable design, and engineering skills to assemble the piece. A window must fit snugly into the space for which it is made, must resist wind and rain, and also, especially in the larger windows, must support its own weight. Many large windows have withstood the test of time and remained substantially intact since the Late Middle Ages.
Swarovski Crystal isn’t a gemstone or even a crystal: it’s a form of glass made at high temperatures by melting silicon oxide powders with lead to form what is known as lead crystal. The exact process is patented by Swarovski but it has approximately 32% lead content to increase the crystals refraction index to resemble that of a diamond. To produce a diamond like effect the crystal glass is precision cut and then polished again by a Swarovski patented process that gives the crystal a high quality finish.
The crystals are often further enhanced by coating the glass with an Aurora Borealis or AB coating that gives the surface a rainbow like appearance to simulate dispersion from a diamond. Swarovski crystal is not as hard as diamond so its susceptible to scratches and chipping from wear and tear, but it’s harder than standard glass.
Tack fusing is the joining together of glass, with as little change to the shape of the pieces as possible. Tack fusing may be used either decoratively, or to assemble a large piece of glass from laminations.
Where tack fusing is used to apply small decorative details to a larger piece, you might want to partially melt the small pieces so that they change shape, usually becoming more spherical under the influence of surface tension, but without changing the shape of the carrier piece. This can be done by using an increased temperature, but only briefly. The carrier piece has a larger thermal mass, so heats up more slowly than the small decorations.
The vitrigraph process usually uses a Paragon Caldera kiln to make glass stringers. The clip-on bottom of the kiln is removed and set aside. The kiln body is put on a thick ceramic rectangle with a central hole. The rectangle is put on two wall brackets or any stable structure away from the floor.
A crucible of glass is put in the kiln and, as it heats, the moulten glass falls through a hole in the crucible to form long stringers. Skilled artists can control the thickness of the stringers and can even draw with the glass as it comes out.
The Caldera needs a 500mm x 400mm x 50mm rectangle, which we cut for you from a much larger sheet. Normal kiln shelves are made from cordierite: a very dense hard ceramic. A suitable-size rectangle would be fairly heavy and hard to cut and drill, so we we use ceramic-fibre board. Ceramic-fibre rectangles are in the on-line shop.
Ceramic-fibre board is made from vacuum-formed fibre. It doesn't retain heat, has a low thermal conductivity, and is stable at temperatures up to 1430°C. If you need to trim it, use a knife, handsaw, or electric jigsaw, but cut it neatly because, as it's fibrous, you can't use a file or sandpaper successfully.
When you work with any fibrous material, don't get the fibres on your hands or breathe them in: ideally, you should put on gloves, wear a HEPA dust mask, use clear protective glasses, and wash your hands afterwards.
The term warm glass refers to fusing, slumping, and other glass processes which take place at temperatures between about 600°C to 925°C. Although that doesn't sound warm, it is when you compare it to glassblower's working temperatures, which often exceed 1100°C. Warm glass is sometimes called kiln-formed glass.
A BRIEF INTRODUCTION TO CLAYS
Clays are formed naturally over millions of years as rocks break up into minute particles. They consist of hydrous aluminium silicates and other compounds such as feldspar, iron oxides, mica, and quartz. Clays are collectively referred to as ceramics.
Clays are often divided into three main categories: earthenware, porcelain, and stoneware. Generally, they needs to be fired for several hours, although the exact chemical composition affects the firing temperatures and times, and the clays' colour, porosity, shrinkage, and strength.
All clays are created to mature at specific temperatures, and any variance can lead to unsatisfactory results in ceramic durability or color. If fired too high, clay can deform or even melt; if fired too low, your pieces will be dry, rough, and potentially unsolidified.
Historically, low-fire has been the most commonly used firing range due to limitations in kiln technology. Modern kilns are now capable of much more complex, high-temperature processes, but low-fire range continues to be popular because it allows ceramic artists to use a variety of colourants that either burn off or become unstable at higher temperatures.
The maximum cone rating of a stoneware or porcelain clay is the temperature at which it vitrifies. This is the hardening, tightening and finally the partial glassification of the clay. Vitrification results from fusions or melting of the various components of the clay. The strength of fired clay is increased by the formation of new crystalline growth within the clay body, particularly the growth of mullite crystals. Mullite is an aluminum silicate characterized by a long needle-like crystal. These lace the structure together, giving it cohesion and strength.
When clay vitrifies it gets very strong. This is especially important for dinnerware where pieces are exposed to a lot of abuse. Vitrification also makes the clay's porosity low.
EARTHENWARE, PORCELAIN, AND STONEWARE
Earthenware is normally beige, red, or white. It has the lowest firing temperature of the three, usually lower than 1150°C. It's slightly porous, and stains and chips easily, so it's often glazed to protect the surface. Its porosity means it's good for making terracotta planters and oven steamers, but not good for jugs or vases.
Porcelain is composed of kaolin, or china clay. Kaolin doesn't melt until 1800°C, so other compounds are usually added so it can be fired between 1250°C and 1400°C. For example, bone china is made by adding bone ash to the clay. It's known for its whiteness, hardness, smoothness, durability, and translucency. When tapped, it makes a distinctive ping: or ming.
Named after a hill in China from which it was mined for centuries, kaolin is the purest form of clay and is the foundation of all porcelain clay bodies. Though pure kaolin clays can be fired, often they are mixed with other clays to increase both workability and lower the firing temperature, so if using a kaolin-based clay body, be sure to note how pure your material is, as this will change the required temperature.
As a clay body, porcelain is known for its hardness, extremely tight density, whiteness, and translucence in thin-walled pieces. Another difficulty with porcelain bodies is that they are very prone to warping during drying in the kiln
When fired, porcelain becomes a hard, vitrified, non-absorbent clay body, very similar to high-fire stoneware. It also develops a body-glaze layer formed between the clay body and the glaze. The absence of any iron, alkalies, or alkaline earths in the molecular structure of kaolin not only dictate its high-fire requirements, but are also responsible for its most identifiable characteristic: its white color.
Stoneware is normally beige, grey, or red-brown. It's usually fired between 1150°C and 1300°C. It's hard, durable, and resists thermal shock. Glazes bond well, so it can be made waterproof.
Stoneware is a plastic clay, often grey when moist. Getting its name from the dense, rock-like nature of the clay body when fired, stoneware is typically combined with other clays to modify it, such as ball clays which might be added for plasticity. It is important to note that stoneware is divided into two types: mid-fire and high-fire.
Like low-fire bodies, mid-range stoneware is relatively soft and porous and has a clearly separate glaze layer after firing. However, a mid-range firing results in increased durability of the ware as well. When fired, stoneware ranges in color from light grey to buff, to medium grey and brown.
Mid-range glazes typically mature between Cone 4 and Cone 6, and most commercial underglazes have a maximum temperature of Cone 6. These glazes are more durable, still offer a fairly extensive color range, and though not quite as harsh as low-fire glazes, can still be quite bright.
Bisque is clay which has been fired once, without a glaze, to a temperature just before vitrification. Firing changes the clay into ceramic material, without fully fusing it. A second, slower, firing melts the glaze and fuses it to the clay body.
Bone china is a type of porcelain composed of bone ash, feldspathic material, and kaolin. It's the strongest of the porcelain or china ceramics, having very high mechanical and physical strength and chip resistance, and is known for its high levels of whiteness and translucency. Its high strength allows it to be produced in thinner cross-sections than other types of porcelain.
From its initial development and up to the latter part of the 20th century, bone china was almost exclusively English, with production being effectively localised in Stoke-on-Trent. Most major English firms made or still make it, including Fortnum & Mason, Mintons, Coalport, Spode, Royal Crown Derby, Royal Doulton, Wedgwood, and Worcester.
In the UK, references to china or porcelain can refer to bone china, and English Porcelain has been used as a term for it, both in the UK and around the world.
Polymer clay is a man-made material: tiny particles of polyvinyl chloride mixed with plasticisers and pigments. When it's baked, at around 125°C, the particles fuse and the clay hardens.
Raku was originally a Japanese technique, but it's now become an internationally popular way to make decorative ware, with each piece having a unique blend of colours.
A bisque piece is fired to about 950°C, then glazed. It's removed from the kiln when red-hot, and put straight into a container of combustible material.
The flames, reducing atmosphere, and mix of chemicals stain the clay. When the piece is removed and quenched in cold water, interesting colours and shades remain: often unpredictable.
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