Raku Frequently Asked Questions Part 1of 2
Compiled 5/31/96 by Steven Branfman Author, ?Raku: A Practical Approach, Second Edition? and ?The Potters Professional Handbook? The Potters Shop 31 Thorpe Rd. Needham MA 02494, 781/449 7687 Revised 9/02 Last Posted 8/16/03 COPYRIGHT (C) 1996. All rights reserved. Contact the author for permission to issue a copy in any form.
R.0 What is Raku? R.1. Didn't Paul Soldner invent raku? R.2. How do pit, sawdust, smoke firing, and raku differ? R.3. Isn't raku a once-fire process where you don't have to bisque first? R.4. Is raku suitable for functional use? R.5. What constitutes a raku clay? R.6. What is a raku glaze? R.7. Which cones do I use in raku? R.8. How do you get those bright metallic effects? Sometimes my glazes don't crackle as much as I like. What can I do? R.9. All I ever get are bright metallic effects. How do I get more colorful glaze effects? R.10. Can I preheat my pots in the kiln as it is warming up (starting with a cold kiln)? R.11. Must I use a certain type of kiln or can I fire raku in an electric kiln? R.12. When it comes to kilns I?ve heard the terms flue, damper, stack, and chimney. How do they apply to raku kilns? R.13. Why can't I reach temperature no matter how much gas I use? R.14. Don't the tongs used to lift the pots leave marks? R.15. I?m confused about the term ?reduction.? Can you explain what this means? R.16. Must I remove my ware from the kiln to apply post firing reduction or can I insert reduction material into the kiln chamber? R.17. Do different types of reduction material give different effects? R.18. Must their be clouds of smoke when doing raku? R.19. What is ?smokeless raku?? R.20. What is meant by ?slip resist? in raku?
R.0 What is raku?
Raku is a pottery technique that has it?s origins in 16th century Japan. We are pretty sure that it was developed by Korean potters under Japanese rule but the exact circumstances of it?s development and in what context it was discovered is a mystery. The raku technique, like other pottery techniques such as salt glazing and pit firing, primarily revolves around it?s firing process although involvement with raku often goes much deeper into its philosophy, roots, and cultural significance. Traditional raku and our western version of raku are similar in many ways though there are some significant differences.
To briefly describe the raku process we must understand that most all other types of pottery are loaded into a cold kiln where the firing proceeds slowly until the desired temperature is reached. This firing cycle may take anywhere from 8-24 hours or even longer. When the kiln has reached temperature (which is generally determined through the use of pyrometric cones), it is shut off and allowed to cool enough to be able to remove the ware using bare, or lightly gloved hands. The cooling cycle may last from 12-24 hours or longer. The ware is considered finished when it is taken from the kiln. In raku, the pieces may be loaded into a cold kiln but are often preheated and loaded into a hot kiln. The firing proceeds at a rapid pace with the wares reaching temperature in as short a cycle as 15-20 minutes (though raku firings can last up to several hours depending on the individual pieces and their firing requirements). Glaze maturity is judged by the trained eye without the use of cones or measuring devices. When the firing is determined to be completed the wares are immediately removed from the kiln. Since at this point the glaze is molten, tongs or other lifting devices are used.
This is the stage in the process where traditional and contemporary raku differ in technique and treatment. In our western version the wares are now treated to a ?post firing reduction? phase. The wares are put into a container with combustible material such as sawdust, or leaves and allowed to smoke for a predetermined length of time. The carbonaceous atmosphere 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 wares have cooled, they are washed with an abrasive cleaner to remove all residue of soot and ash.
R.1. Didn't Paul Soldner invent raku?
Not exactly. Soldner is an innovator and one of a few responsible for popularizing raku in this country beginning in the 1950's. Raku was first developed by Korean potters under Japanese rule in the 17th century. The circumstances that led to its launch and spread are somewhat of a mystery though.
R.2. How do pit, sawdust, smoke firing, and raku differ?
These types of firings are often confused with each other because they can share some similar characteristics. Briefly, raku ware is fired in a more or less conventional type kiln where glaze technology is understood and utilized. The others are forms of primitive firing where temperatures reached are generally lower and glazes are not commonly used. In primitive firings, the "kiln" may consist of a simple hole in the ground (ie, a pit).
R.3. Isn't raku a once-fire process where you don't have to bisque first?
Raku firing greenware is a sure way to line the bottom of your kiln with shards. Always bisque-fire to at least Cone 08 before glazing and raku firing.
R.4. Is raku suitable for functional use?
The traditional use of raku ware in the Japanese tea ceremony has contributed to confusion about the functional use of raku. With very few exceptions, all raku fired ware is fragile, porous, and generally unsuitable for functional use. Unless such fragile ware is treated post-firing with a non-glaze material, such as a polyurethane or acrylic sealer or an oil of some kind, the pots will sweat water and eventually breakdown. Treat raku as decorative. The occasional use of raku in a functional setting is OK but keep in mind that the glaze is soft and can be easily chipped and end up being ingested. If you must use your pots for food try to limit the use to dry food. The fragility of the ware also renders the reliability of handles and other appendages extremely questionable.
R.5. What constitutes a raku clay?
A raku clay is any clay that can be successfully raku fired. That includes most any type of clay out there! As I say at my workshops; "I've never met a clay that I couldn't raku." Generally though, a clay suitable for raku needs to contain a lot of fireclay and similar refractory materials so that it can withstand the sudden heat shock of the raku process. This includes most stock stoneware clays. The clay does not have to be loaded with coarse grog but it does have to be open enough to expand and contract without cracking. Most clay suppliers can help you choose an appropriate claybody. The other characteristics that you are looking for are your personal ones such as plasticity, color, texture, etc. Nothing needs to be sacrificed in order to have a good, reliable raku clay.
R.6. What is a raku glaze?
Similar to the question of raku clays is the answer to this question. Any glaze that you can successfully raku fire is a raku glaze. The most important factors in identifying raku glazes is the temperature at which they mature, how you plan on using them, and what kind of effects you are looking for. You must also keep in mind that if you are using a variety of glazes on the same pot or in the same kiln load, unless you know that they all mature to your satisfaction at around the same temperature, you will be faced with varying degrees of maturity. However, just because a glaze is formulated to fire at a temperature higher than your usual range doesn't mean that you should eliminate that glaze from your pallet. Experiment with your glazes to achieve a variety of surface effects from dry textures to surfaces with a high gloss. Don?t limit yourself to homemade or personal glazes either. Try low fire commercial glazes for some unusual results.
R.7. Which cones do I use in raku?
The only cones that should be used near a raku kiln are ice cream cones. Because of the fast firing, varying atmosphere, multiple loads and other factors, pyrometric cones are generally poor indicators of heat and temperature so they are not used. Most raku potters fire their wares using the actual glaze melt as the visual indicator of maturity. Many potters, however, do use pyrometers or cones to warn of coming glaze maturity and then check the ware visually through the peephole(s). It takes some temperature of raku depends on the glazes that you are using. Most raku is fired in the range of cone 010-06. You must remember though that you as the maker of the pots are the final expert on whether a glaze is mature, underfired, or overfired. If a glaze is not glossy enough, doesn't have the expected crackles or metallic effects, or doesn't exhibit any other characteristic that you find desirable, you need to adjust the firing.
R.8. How do you get those bright metallic effects? Sometimes my glazes don't crackle as much as I like. What can I do?
Assuming you are using the correct glazes, both metallic effects and dark crackle lines are a result of firing the glazes to their maximum maturity followed by a fast post-firing reduction technique. You must quickly get your pot from the kiln to the reduction container and covered before the pot has a chance to cool too much, otherwise the post-firing reduction will not be effective. Pronounced crackle effects are also often dependent on a thick application of glaze.
Continued on Raku FAQ part 2 Steven Branfman The Potters Shop
31 Thorpe Rd, Needham MA 02494 phone: 781/449 7687 fax: 781/449 9098