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.

How to Remove Tea and coffee stains from your Ceramic Mugs

It is a common occurrence for mugs used everyday to become badly stained by tea or coffee. The brown stains are unsightly and difficult to remove. Sometimes they become so bad that scrubbing in soapy water does not remove them. Clearly coffee and tea are strong staining agents!

"But what causes the staining?"
It is a combination of hard water, chemicals called tannins, and microscopically rough glaze surfaces. These conditions allow the stains to strongly adhere to the glaze surface. The staining is usually worse in the base of the mug or where there is a sharp corner to hold on to the stain.

"So how do I clean stained mugs?"
Various cleaning methods have been tried and tested including vinegar, bleach, baking soda and washing soda. All have been proven to be successful and are widely used. However Bar Keepers Friend and tooth cleaning powders are less likely to give long lasting damage to the glaze surface. Cleaning with other chemical compounds and scourers whilst successful can create damage to the glaze surface which will make them more susceptible to future staining. So please take special care with your best china or dinnerware and treat them gently for their long term protection.

"So how do I stop staining?"
Manufacturers of the top brands of dinnerware and mugs design their products to resist staining and damage in use. In essence this is done by ensuring the glaze is chemically and physically durable. However,with the widespread manufacture of mugs in many parts of the globe including Asia, it is not easy to know the source and quality of the ceramic mugs we buy.It is almost impossible to assess how resistant mugs will be to staining by visual inspection. Smooth glaze surfaces with few corners will reduce the potential for the stain to adhere strongly to the surface. However, over time the glaze surface may be attacked by dish-washing agents. leading to the dreaded staining.Cleaning the pottery soon after use with warm soapy water will certainly reduce the possibility of staining.

"Summary"

To reduce tea and coffee staining of your mugs, clean them as soon as possible after use in warm soapy water. Use quality mugs from top brands as they will have designed the mugs to be chemically and physically durable. Avoid harsh detergents for cleaning as this can damage the glaze surface and lead to greater staining. Bar Keepers Friend and tooth cleaning powders are preferred cleaners and less likely to create long term damage. If all else fails buy new quality mugs but recycle the old ones. Pottery is a truly 100% recyclable product!

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.

Is Your Pottery Microwave Safe?

Microwave ovens are now a common feature in most kitchens. Their use both to heat and cook food means a wide range of ceramics is being used in microwave ovens. However the question remains….Is all pottery microwave safe?

Technically this question is a little more complex than it appears. There are general rules such as:-
“do not use ceramics decorated with gold, silver or precious metal in microwave ovens”

 Indeed ceramic with any metal should not be used in a microwave oven. However additional rules depend on recognising which type of ceramic is being used. For the consumer this is not an easy task.

All ceramics are not the same!

Ceramics are now made all over the world and it is not always easy to establish their source or quality or type. However ceramics that have been fired to a high temperature and are non porous are generally considered to be acceptable for use in microwave ovens. These ceramics include stoneware, porcelain, bone china, and vitreous cookware. Other ceramics which have not been fired to a high temperature have to be used with caution. For these type of product to be used safely there is a need to ensure that they are both dry and have not absorbed water. This can happen in many circumstances particularly during washing or in storage in the fridge. These products need extensive safety instructions to be used safely.

Top brands help the consumer by labelling their products as ‘microwave safe’. Less well known products cannot give this assurance and often do not label at all. So buyer beware and if in doubt do not use in a microwave. Look out for BS or CE standards as a sign of meeting a quality standard.

In summary, most high fired ceramics are suitable for microwave oven use. Lookout for the labelling used by branded products to give reassurance on acceptability for microwave oven use. If in doubt “keep out” is a good motto to remember!

Why not test your pottery knowledge with my quick pottery quiz

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.

Top 10 Pottery Making Tips for the more experienced Potter

Pottery making is a fun but sometimes frustrating hobby. You never know exactly what your results will be when you open that kiln door! Here are my tips to make pottery making that little bit more rewarding......

1. Keep records of everything you do-that way you learn quickly and can repeat your successes and avoid your failures.

2. Label your buckets not your lids- don't learn the hard way that you have just glazed your speciality piece in the wrong glaze!

3. Buy a kiln with a modern controller. Modern controllers are now relatively inexpensive and give you such freedom to control the firing in a way that best suits your product.

4. Keep drying of your product consistent. Drying too quickly is one the most common causes of glaze or clay faults.

5. Learn something about the materials you use. Armed with a little knowledge you can save so much time.e.g. Does glaze go off? What happens to my clay if it freezes?

6. Keep your clay in good condition by covering it with plastic when not in use. That way it retains its plastic condition.

7. Plaster moulds need to be replaced after 40-50 casts. It is false economy in slip casting to continue to use old moulds. These may give inconsistent thickness, pinholed ware and much more besides!

8. Use Orton cones or Bullers rings in your kiln. That way you know your kiln is performing OK and you can spot potential problems such as element failure before they become disastrous.

9. Give some pieces to your loved ones or to charity. The feel good factor will keep you motivated.

10. Continue to share your passion with others. Go to pottery classes and learn something new or join an online pottery group.



Alternatively why not test your pottery knowledge with my quick pottery quiz

More information and other technical articles on pottery and ceramics can be found at my website www.pottersfriend.co.uk

Go now to sign up for my free newsletter.

How to avoid scratching your dinnerware

So why does it scratch?

A scratch on a plate at high magnification

Pottery is hard and strong! If you don't believe me try cutting it with the sharpest steel knife you have. Whilst it may mark it will not break. Steels used in everyday cutlery are softer than pottery glaze!

To scratch a pottery glaze you need a material of similar or greater hardness. So pottery can scratch itself. Glaze on glaze contact will cause surface damage and when there is excessive or repeated damage the eye sees it as a scratch!

So a scratch isn't a scratch until you can see it!
Glazed pottery is susceptible to surface damage as soon as it comes out of the production kiln. During the manufacturing process care is taken to avoid excessive damage by careful handling of the pieces, the use of protective sleeves and optimum packaging for transport.

However in our homes damage to our pottery happens all the time. For example each time we use a plate it is damaged by contact with other pottery. Creating a plate stack to clear the table, placing plates on each other in the sink, washing them in detergent, sliding them into clean stacks all contribute to damage. Clearly there is a cumulative effect of this damage which results in the appearance of scratching.

So how can scratching be avoided?

Taking care to handle the ware gently, in a similar way to the manufacturer, will extend the life of the pottery. Using protective sleeves and avoiding sliding contact are particularly important. In addition the ware can be adversely affected by detergents and strong acids so prolonged contact with these chemicals should be avoided.

Whilst these precautions may seem fanciful and few people will take the time or effort to follow them, they do work!

Alternatively, if all this is too much then there is one other thing you can do......buy pottery that has a glaze that is not highly glossy and has a less than mirror like finish! Whilst this does not reduce the damage, scratches normally visible to the naked eye are less apparent, and the ware appears less scratched.

Alternatively why not test your pottery knowledge with my quick pottery quiz

More information and other technical articles on pottery and ceramics can be found at my website www.pottersfriend.co.uk

Go now to sign up for my free newsletter.

How to choose your kitchen or bathroom DIY ceramic tiles

Introduction
Planning and upgrading your bathroom or kitchen is not always an easy task. You are full of enthusiasm but are faced with lots of choices. The choice of ceramic tiles is bewildering. Usually colour, design and budget are the key factors affecting your choice. However I would add a further factor ‘technical performance’. Remember all tiles labeled as ‘ceramic’ are not the same. Indeed some natural mineral tiles such as slate or marble sometimes use the same terminology.

To most people tiles are tiles – aren’t they? Well no! You need to know there are at least 2 categories of ceramic tile; floor tiles and wall tiles. What makes them different is ‘technical performance’. They are both usually made of ceramic, they can both be glazed with a shiny surface and both can be highly coloured with designs. However they do not have the same technical performance in use!

Wall tiles
Wall tiles are usually porous (on the back) and have a highly glossy glaze finish on the face. This allows them to be hygienic, cleanable, and not absorb moisture on the face when exposed to wet conditions in bathrooms and kitchens. However in manufacture they are normally fired in a fast fire kiln in less than one hour. This means they have limited strength, abrasion and slip resistance.

Floor tiles
In contrast floor tiles are fired to a higher temperature usually with a special glaze coating. This gives a much increased strength, abrasion and slip resistance. Clearly this gives advantages when used under foot where stronger tiles are less likely to crack, scratch or wear out as well as resist slipping. Indeed a number of standards need to be met for tiles to be considered suitable for floor tile use. So choose wisely for your location. Floor tiles for floors, and wall tiles for walls!

Colour and finish
A second consideration is tile finish and colour. Although this is generally down to individual taste, for best slip performance floor tiles have a dull gloss or matt texture. Wall tiles can have a much wider range of textures and gloss but a smoother finish is usually more easily cleaned than a textured finish. Please be aware that although most tiles supplied in a box set are matching in design and colour they are not identical!

Quality
Probably the most important aspect of tiles is the quality of manufacture. This is not easy to assess. It means how strong are they? How long will they last? How flat are they (tiles warp during manufacture)? How easy are they to install?

Although most tiles supplied by reputable suppliers are manufactured to European standard BSEN14411 or American ASTM standard equivalents, it is not readily apparent by how much they exceed these standards. In Europe the CE Mark is a sign of quality adopted by tile manufacturers. Established brands like Marazzi or Porcelanosa are constantly pushing the boundaries to produce consistent products which exceed expectation in terms of quality, design and performance.

Summary
In summary, take a little time to choose the right type of tile for your job. Look for the CE marks or the BS standards on the packaging as a sign of meeting a quality standard. Use quality branded products if possible as often they give better performance in use and have been designed for ease of installation.

Is there a future for pottery manufacture in Europe?

This is a big subject and worthy of debate! Over the last 20 years the ceramic industry in Europe has undergone massive change.

The tableware sector (cups & plates etc) in Europe has seen severe downsizing with manufacture shifting to the lower cost economies in China and Asia. The change in consumer habits in western europe to less formal dining has meant a change in perception of pottery from a collectable item to a throwaway one. This is particularly noticeable with the younger generation who want fashionable ware for casual dining.The result has been a massive reduction in demand for the high value products and a growth in lower value products. This has been reinforced (in the UK) by the growth in supermarket sales by companies such as Tesco who constantly drive down prices forcing manufacturers to import or close down. That said there is still a place for the niche manufacturer who can move quickly with new and quality designs. Brand value is still important in this higher end sector.

The giftware sector (figures and decorative ware) has also been hit by the same trends as above. Collectable figures and plates are less popular among the younger generation whilst fashionable branded giftware has been more popular. Again there is a lot of competition in this sector from Asian imports so strong brands and new designs are critical to success.

To answer the question- is there a future -the answer is yes but only for the niche manufacturer who can be constantly innovative and build a brand of value. Speed of new products to market will be a critical factor!

What do you think? I would be happy to recieve your comments.