The Elusive Red Pottery Glaze

Symbolism of Red

Red is one of the most popular colours to be used worldwide. The color red is associated with lust, passion, love, beauty, and danger. In Asia it is a symbol of courage, loyalty, honor, success, fortune, fertility, happiness, passion, and summer.

Consequently many types of asian pottery including the beautiful chinese red glazes of the Sung Dynasty and the exquisite Japanese Imari porcelain feature red as the main colour.

However in more recent times the demand for mass produced red pottery of high intensity and consistent colour has created a real challenge for ceramic engineers involved in pottery manufacture.

Japanese Red
Imari porcelain is the name for Japanese porcelain wares made in the town of Arita, in the former Hizen Province, northwestern Kyūshū. They were exported to Europe extensively from the port of Imari, Saga between latter half of 17th century and former half of 18th century.

Photo of Imari by George Le Gars

Though there are many types of Imaris, Western Europes conception of Imari is associated with the type of Imari produced and exported in large quantity in mid-17th century. This type is called Kinrande and is coloured porcelain with underglaze cobalt blue and onglaze red and gold.

The blue is rich in colour and hue and is based on a cobalt containing pigment. The red colour, however, whilst remarkably bright and interesting is not such a clean hue and is produced using iron oxide or iron based ceramic pigments.

Iron ochres and natural red clays are some of the earliest pigments used by man and continue to be used today particularly in hand crafted pottery of rustic nature.

Rouge Flambe
Similarly many of the early ceramic red colours and glazes used on European pottery were not always pure in colour and were based on copper or gold in colloidal form. These colours were used to copy original Chinese patterns and glazes perfected in the 18th century.

Rouge Flambe by Royal Doulton Co

Interest in reproducing flambe glazes began in about 1855 in France but soon spread across Europe, particularly to England and Germany.

In Britain, the Staffordshire potter Bernard Moore used experimental and highly accomplished red flambe glazes on Chinese-inspired shapes to wonderful effect. Requiring a special glaze formula, firing cycle and condition they were expensive to manufacture and difficult to reproduce.

Shown here is a vase made by Royal Doulton decorated with the spectacular Rouge Flambe glaze.

The Challenge of Pillar Box Red

Red Pillar Box by Ian Britton 
FreeFoto.com

The development of a reproducible pillar box red glaze and decoration has been an elusive challenge for potters and ceramic engineers through the ages.

In particular the large scale development and manufacture of pillar box red colour and glaze for pottery is believed to have taken over eight thousand years to achieve. It was not until the twentieth century that true pillar box red glazes and onglaze colours became widely available for decoration of pottery.

Cadmium Sulpho-Selenide Red Glazes

Red glazes and colours based on cadmium have been available for about 50 years. The early glazes and colours of this type depended heavily on cadmium being added to the glaze as a pigment mixed crystal Cadmium sulphoselenide (CdSSe). However glazes of this type lacked temperature stability above approx 800C.

To overcome this the cadmium was added to the frit batch and subsequently melted into a glassy state. In many cases the frits also contained lead, sulphur and selenium. This type of glaze required firing in a specific way to achieve optimum results. The firing time and the kiln atmosphere were both critical. The best results were obtained using a short firing cycle to a peak temperature of approximately 1000C. Good air circulation in the kiln, and a good separation of pieces were also recommended. Ideally Cd/Se fritted glazes should be fired separately from other types of ware, because fumes from other coloured glazes can affect the colour achieved.

First generation Zircon/ Cadmium Red Glazes

Actual Red

Target Red

In the 1970s ceramic engineers in Europe developed a new generation of red colours and glazes. These were totally different in nature as they were based on a zircon encapsulated cadmium pigment. These were patented in 1973 by Broll et al of Degussa.

Briefly encapsulation  means that at microscopic level the cadmium is surrounded by the zircon crystal. This gives two major advantages. The pigment is more temperature stable up to 1200 celsius and more chemically stable thus giving lower cadmium release after firing and exposure to acids. These types of red glaze could be used on a variety of firing schedules and were infinitely more flexible in use.

However these pigments had a serious drawback which limited their widespread use. They lacked intensity and consequently needed high pigment loading to give any degree of colour saturation.


Second and third generation Zircon/ Cadmium Red Glazes

Red Vase by Newland Pottery BV

In the last 20 years or more the encapsulate type of pigment has been developed further to the stage where intense pillar box red coloured glazes (see target above) are now possible. These pigments have allowed more stable sanitaryware glaze colours to be produced where high temperatures in excess of 1250C are used. In addition they are suitable for use in a range of glaze and onglaze colours as they are mixable with other non cadmium based colours.

China is the major manufacturer of these types of pigment as they have proven to be a lower cost supplier of intense encapsulate pigments.

The challenge of the stable pillar box red glaze now appears to have been met by ceramic engineers. The  stable cadmium encapsulate pigment is being used by most pottery manufacturers and appears to meet current legislation in many parts of the world. However cadmium is still an emotive word for many being considered a toxic element in much the same way lead. So who knows? Will the journey to find a new pillar box red start all over again? What do you think?

This article was inspired by the recent publication of  a book entitled THE DEFIANT RED by my friend the highly respected ceramic expert Leen W Baaij.

More information and other technical articles on pottery and ceramics can be found at my website The Potters Friend. Go now to sign up for my free newsletter.

How to Buy Your Ceramic Dinnerware

Fashion is a strong reason to buy

For the discerning shopper selection of dinnerware is primarily based around fashion. In today's fast moving world, where casual dining has become the norm, our dinnerware often reflects our taste in food or the environment in which we use it. For example Mexican food might well be served in brightly coloured dishes decorated with peppers, spices and other vegetables reflecting the type of food we might eat..However the technical issues are a lot harder to assess and should also be valued highly!

What is ceramic dinnerware?

The word ceramic was derived from the greek word 'Keramos' meaning 'earthen vessel'. The word has now been applied to a wide range of products from terracotta to the finest bone china. Dinnerware and tableware are just two of the categories often used by stores to describe the end use of this range of ceramics.

What type of ceramic is it?

Many types of ceramic are on display in shops and stores. These include terracotta, earthenware, stoneware, porcelain and bone china.

Often it just says china on the box but this means nothing as it is just another broad term implying it is a ceramic! But we already know that!

So just how do we identify the different types of pottery?

One way is to look at the colour of the body under the shiny glaze. The best place to do this is under the foot of the item as this is often unglazed. In order of pure whiteness the following is a generalised guide to the colour.

Terracotta bright red to red brown body colour

Stoneware pale brown to buff colour

Earthenware ivory to off white

Porcelain off white to blue white

Bone China creamy pure white

Bone China and Porcelain

Porcelain and bone china can be more easily differentiated from the rest by their translucency. This means that they they let light transmit through the piece. If you hold a delicate piece of bone china or porcelain up to the light, and wave your hand between the plate and the light, you can see a shadow of your hand through the piece

The technical stuff

What does it all mean?
Once you know the type of ceramic you have some idea of the technical properties. Firstly it is a guide to the strength of the piece and means resistance to chipping,cracking and breakage. Secondly it is a guide to the cost. High quality bone china and porcelain manufacturers use highly refined materials and processes to 'design in' the whiteness,translucency and strength required by consumers. Consequently the cost is higher. However because of the inherent strength you might expect this type of pottery to last longer in use!

As in life things are never quite so simple. The manufacturers of other types of dinnerware (terracotta, stoneware,and earthenware) compensate for their lack of inherent strength by making chunkier pieces. All types of ware can be highly decorated with colour so this is not the differentiator.

So the shopper has a choice of chunkier less white designs or whiter more delicate designs!

What about dishwashing?

The chemical resistance to acids and washing detergents is also worth considering. Generally higher fired glazed tableware such as porcelain and stoneware have a higher intrinsic chemical durability and are 'unleaded' but this is not always the case.
Top brands now indicate their testing to BS or FDA standards and indicate their quality by labelling with 'dishwasher safe' and 'unleaded' or 'lead-free'. The Kite mark is also used as a sign of quality manufacture in the UK manufacture. The astute shopper therefore needs to look for these labels in determining value for money.

Fashion and technical performance are both important
In summary,shopping for dinnerware can be an enjoyable experience! Armed with a little technical knowledge it can be so much easier! Give at least equal weighting to to the technical performance as to the fashionable design in choosing your ceramic tableware.

More information and other technical articles on pottery and ceramics can be found at my website The Potters Friend. Go now to sign up for my free newsletter.

Cheadle's Pugins Gem

One of my favourite places

Once upon a time in a small market town in Staffordshire, England, an amazing church was built by a not so famous architect. The same man also designed the Houses of Parliament and Big Ben. St Giles RC church, because of its beauty and spectacular gothic architecture, became known as Pugin's Gem and has featured on both the BBC and Channel 4  in recent years.

That man was Augustus Welby Northmore Pugin, and he is now regarded as being responsible for the revival of Gothic architecture in the UK in the nineteenth century. In a recent BBC documentary, his influence on architecture was likened to that of Darwins influence on science.

2012, was the Bicentennial of the birth of Pugin and it was celebrated in style in Cheadle, a relatively unknown town that sits on the edge of the beautiful Staffordshire Peak District. A series of events,workshops, tours and exhibitions were staged throughout the year based around the church, the nearby Pugin Centre,and other local Pugin buildings. The legacy is the Pugin discovery and heritage centre which is sited at the centre of the High St.

The church itself is open to visitors most days and really should not be missed. Put a coin in the slot, sit back and be amazed as the church  is revealed in all its splendour. You will not be disappointed. To appreciate the church in full obtain an audio guide first from the Pugin Centre and allow it to guide you around the features of the church.

If you are travelling close to Staffordshire Peak District this year why not spend a little of your precious time to visit the not to be forgotten Pugin's Gem. There's also a chance to discover more of the Secrets of Cheadle, which lies only a few miles from Alton Towers resort and the scenic Churnet valley with its Steam railway and excellent country walks.

To find out more about Cheadle and how to get there why not visit the Cheadle,Staffordshire website Cheadle Staffordshire

2012 The Year of the Small Business?

After the doom and gloom of 2011, a year when banks, the public sector, big business and especially retailers have suffered, perhaps 2012 is the year for the small man. The year when the public begins to recognise that what they have locally really is worth keeping. And that should include the local butcher, the local tradesman and the local potter.

Yes the local potter!

I was fortunate to meet a number of innovative potters at the 2011 Ceramic Festival in Stoke on Trent, England. Despite the current climate they continue to create innovative designs and concepts.

One such company with years of experience in modelling and design of unique ceramic wares is Sculpta Ceramics. The expertise of individual potters like this should not be underestimated. Designing unique wares for children, and local heritage are all part of the range of products from local man Nathan.

Another local artist Alison Morgan is the creator of Cityscape Ceramics, a unique range of ceramic art. Each piece is inspired by an iconic skyline and features well known and loved landmarks.

During my visit to the festival I even managed to buy a ceramic bottle kiln jar to add to my collection.

So next time you want that special present or gift don't overlook your local potter. They may not be on the high st but many will be only too pleased to show you their wares!

More information on pottery and ceramics can be found at my website http://www.pottersfriend.co.uk Go now to sign up for my free newsletter.

My Favourite Thing -A Hand Lens

Pottery hobby or interest in Minerals or Plants?

Some people just love gadgets particularly the new electronic ones. However here is one that has stood the test of time. Its just a hand lens- a magnifier you might say-but such a valuable piece of hobby kit.

Whether you want to look in detail at that pottery fault, or check there isn't a crack before you fire a piece this hand lens will save you so much time and money. Other interests such as looking at crystal minerals and fossils up close are also catered for.

Perfect Present For a Potter

A hand lens that lets you see the problem.

So often when you are learning to make pottery the results are not as you would expect or wish for. The piece has a small fault., a large speck or change in colour, just where you can see it! Use this neat little hand lens to see what really caused the fault.

Make sure that next time that perfect piece you made for a friend really turns out that way. Perfect

In this case it was possible to identify that the colour has crawled back leaving an area without colour.

Lenses or Loupe

The Same Thing!

Whether you are buying a magnifier for your pottery hobby or for studying the detail on jewellery, different names are often used. For example lenses used for looking at jewellery are often called loupe. In real terms they are all a magnifying lens.
However, the quality of lens determines the quality of image. So choose the best you can afford for something you will keep for a lifetime!

More information on pottery and ceramics can be found at my website http://www.pottersfriend.co.uk Go now to sign up for my free newsletter.

How to properly fire your pottery

The firing of pottery goes back over 3000 years. In those days wood fires were the source of energy. However today so many other forms of energy are available including wood, coal, gas, electric, oil, microwave, wind, solar to name just a few.

For the small pottery craft studio or hobbyist however the most common means of firing pottery are by the use of gas or electric kilns. Generally electric firing is a clean means of firing whilst gas is thought to be more energy efficient. Let us consider the basics of each:

How does electric firing work?

The principle of electric firing is relatively simple. Imagine a box or cylinder kiln fitted with heating elements like your domestic oven. However, instead of heating to 300C it is capable of heating to 1300C.

Operation of the kiln starts when electricity is applied to the elements ( resistive load ) causing them to heat rapidly. The heat is transmitted to the pottery mainly by radiation. Special insulating bricks, called refractories, line the floor,walls and roof of the chamber to prevent the heat generated from escaping. An electronic box, called a temperature controller,linked to a thermocouple (special wire) inside the kiln, measures the temperature constantly in the chamber of the kiln and then controls how much electricity is supplied to the elements. This in turn controls the rate of increase or decrease in temperature within the kiln.

How does gas firing work?

The principle of gas firing is also relatively simple.. Imagine this time that the box is kiln fitted with a burner or burners, a little like your domestic gas oven. However, instead of heating to 300C it is capable of heating to 1300C and because of the large amount of gas used the kiln needs a chimney or flue.

Operation of the kiln starts when the gas is turned on and burner lit. The heat is transmitted to the pottery mainly by convection and radiation causing it to heat also. Special insulating bricks, called refractories, line the floor,walls and roof of the chamber to prevent the heat generated from escaping. A vent in the roof or rear of the kiln leading to a chimney allows combustion gases to be removed from the kiln. An electronic box, called a temperature controller,linked to a thermocouple (special wire) inside the kiln, measures the temperature constantly in the chamber of the kiln and then controls how much gas is supplied to the burner. This in turn controls the rate of increase or decrease in temperature within the kiln.

How do I fire the kiln properly?

For both electric and gas firing the two critical factors which affect the success of your firing are peak temperature and uniformity of temperature within the kiln. Peak temperature can easily be measured using the thermocouple fixed inside the kiln. Uniformity could also be measured using a series of such thermocouples located in different sections of the kiln. However this would be an expensive option for smaller kilns.The use of Bullers Rings or pyrometric cones to confirm the consistency and uniformity of firing at different locations within the kiln is more cost effective.These ceramic cones or rings can be placed next to your ware and will experience exactly the same amount of heat as your item. By measuring the values of the rings or cones after each firing you can be assured the firing is consistent from one firing to the next.

But what is the peak temperature?

The peak temperature on firing biscuit or glaze is the maximum temperature reached on firing. This value depends on the type and composition of the clay body and glaze used. As there are literally thousands of body and glaze compositions,suppliers of body and glaze products therefore recommend a peak temperature or ring or cone value equivalent suitable for optimum firing their products. It is advisable to follow their recommendation.

But what if the temperature isn't consistent?

Quite often there is a spread of temperature within the kiln. It is quite common to have a 20 C spread in temperature between the bottom and top of even small kilns. The reason for this is dependent on a number of factors. Rate of firing, kiln design and condition (age and condition of brickwork),element condition and age (for electric kilns) gas/air ratios and flame (for gas kilns) and ventilation aspects of the kiln are all key factors.

For uniform firing of kilns a slower temperature rise to peak temperature and a soak at peak temperature will reduce variation of temperature within the kiln. Indications of non uniform firing of glazed pottery are variation of gloss, colour and or bubble between similar fired pieces.

Summary

Peak temperature and uniformity of temperature are the key factors determining the success of your pottery firing. Peak temperature is measured using a thermocouple connected to the digital display of a temperature controller. Uniformity is measured using Bullers rings or Cones placed in the kiln next to the ware. The heating rate has an affect on both and should be relatively slow for best results. A cycle of more than 12 hours cold to cold is quite common. However you should be guided by the body or glaze supplier as they know the optimum cycles for their products.

More information on firing of pottery and ceramics,including Bullers rings and Orton cones, can be found at my website http://www.pottersfriend.co.uk Go now to sign up for my free newsletter.

Raku Pottery

What is Raku Pottery?

Raku is a pottery technique that originated in Japan in the 16th century. The technique involves a specific rapid firing process at a relatively low temperature but the whole process can be much more complex.
The technique has developed and there is now the traditional Raku and a western version of Raku. The results of this type of process are very unique from other firing techniques, and some fantastic metallic finishes, crazing and other decorative effects can be achieved.

The process in brief

In raku, the pottery pieces are loaded into a cold kiln (for multiple batches pieces are often preheated and loaded into a hot kiln). The kiln is heated rapidly with the ware reaching temperature in as short a cycle as 15-20 minutes.This contrasts with traditional firing cycles of 10 hours or more!

Glaze maturity is judged by the trained eye without the use of cones or measuring devices. Often this is when the glaze has begun to melt.
When the firing is considered to be complete the ware is immediately removed from the kiln while still red hot using tongs or another lifting device.This is the stage in the process where traditional and western raku differ in technique and treatment.

In the western version the ware is treated to a post firing reduction. To achieve this the hot ware is put into a container, usually a garbage can, with combustible material such as paper, sawdust, or leaves and allowed to smoke for a predetermined length of time (usually about 20 mins). The carbonaceous atmosphere (black sooty smoke) reacts and affects the glazes and clay and imparts unique effects and surfaces to the wares. Some of these effects are metallic and crackled glazes surfaces and black unglazed clay.

When the ware has cooled, it is washed with an abrasive cleaner to remove all residues of soot and ash. In this way it is possible to produce a unique piece of art pottery. Unfortunately because of this rapid process the ware is relatively fragile and the decoration not food safe. Pottery made in this way must only be used for decorative purposes.

The Process in detail

The Clay body

Raku bodies are designed so that they allow rapid heating and cooling without cracking. Most raku bodies (but not all) use a recipe that is high in grog (coarse material). A range of Raku bodies are available from suppliers to match your making and firing process.

A typical body recipe might include by parts weight:-

Clay 65-75%
Grog 25-35%
Talc 0-15%

The type and amounts of each component will depend on many factors. These include the clay making process, the fired body colour and texture required and the firing temperatures to be used.
One of the important questions you need to answer "will the glaze and body combination I intend to use give me the glaze finish I require?". For example many glazes used on Raku will readily craze if the correct glaze/body combination is not used. For some this might be an appealing effect. For other Raku makers it may not. So choose your clay body wisely.
The clay body for raku is typically bisque fired to cone 04 (1060C) prior to glazing. This gives it sufficient strength for handling during the glaze firing process, as well as some porosity to aid glaze application.
Most clay suppliers will help you choose an appropriate clay body. Biscuit firing of the clay piece is essential if the pottery is to avoid breakage on firing.

The Glaze

Next you can apply slip, apply glaze, or just leave the pot bare. Any glaze that will melt successfully during the raku fire could be used. The most important factor in identifying potential raku glazes is the temperature at which they mature, how you plan on using them, and what kind of effects you are looking for. Low fire glazes generally give the best results. Most raku is fired in the range of cone 010-06. (900-1000C) Note the surfaces of the pot that are not covered with glaze will however turn black from carbon from the post-firing reduction process.
For more info on Raku glazes see my separate article on Raku glazes.

Raku (glaze) firing

Northern Kilns Raku kiln

The pottery is placed in the kiln and rapidly heated to the point at which the glaze melts. Although a pyrometer is sometimes used to monitor how fast the temperature is rising, Raku artists usually watch the glaze to see when it is ready to be removed from the kiln. Depending on the glazes and technique used, this might be when it gets shiny, or when it bubbles and/or looks like orange peel. Transfer of the ware from kiln to the reduction chamber is important. Speedier transfers can give metallic lustres whilst slower transfer can give brighter colours.

Types of Raku kiln

For firing of multiple loads the temperature of the kiln must also be readily controllable. An electric kiln is perfectly suitable for raku although there are some special considerations that require careful attention. Cut off switches must be used to avoid any contact with live electrical current when the electric kiln is opened. Many types of gas and electric kilns can be used for raku. Kilns need to be located outdoors or in close proximity to the outdoors or have lots of ventilation. Access to the pots inside the kiln is critical so they can be easily removed. Raku kilns are therefore designed to provide this easy access to red hot pots.
More information on Raku firing can be found the Potters Friend website

The Reduction Process

The reduction chamber (garbage can) is prepared by adding the combustibles. There are many things that can be used, but newspaper, sawdust, or wood chips work well and is abundant. After switching off, the kiln is opened and hot piece removed from the kiln with tongs or a lifting device. Immediately it is placed in the reduction chamber (garbage can) where the heat sets the combustibles alight. The lid of the can is replaced and the chamber left for about 20 minutes.

After the pot has completely cooled, it is possible to use Ajax cleaner or similar to clean carbon off the glaze and "shine up" the piece. Reduction is a firing term that refers to a lack of oxygen in the combustion process. By sealing the can with the lid the can is deprived of oxygen. This lack of oxygen causes incomplete combustion of the paper or sawdust to take place and creates the metallic finish on the glaze.

Safety

The raku process is a dangerous process as you will be exposed to high heat, flames and smoke. Always wear fire protective clothing, fireproof gloves and protective eyewear. Do not open or insert tongs into an electric kiln without shutting off. The reduction process (container with combustibles) should take place outside of building due to flames and smoke. Do not apply spray glazes without a NIOSH approved respirator and other personal protective equipment. Although many glazes are Non Toxic and Non Hazardous when used according to manufacturer’s directions, this is not always the case. It is important to check! Raku glazed items are suitable only as decorative ware and are not recommended for contact with foodstuffs.