A crafts forum. CraftBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » CraftBanter forum » Craft related newsgroups » Pottery
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Raku FAQs



 
 
Thread Tools Display Modes
  #1  
Old July 20th 03, 04:49 AM
Tom Buck
external usenet poster
 
Posts: n/a
Default Raku FAQs



Raku Frequently Asked Questions by Steven Branfman

Author of "Raku: A Practical Approach" and "The Potter's
Professional Handbook"
The Potters Shop 31 Thorpe Rd. Needham MA 02494, 781/449 7687
Revised 5/99 Last Posted 6/20/00
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 there 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 its origins in 16th century
Japan. We are pretty sure that it was developed by Korean potters
under Japanese rule but the exact circumstances of its development
and in what context it was discovered are a mystery. The raku
technique, like other pottery techniques such as salt glazing and
pit firing, primarily revolves around its 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 break down. 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 are
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 pallete. 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 depending 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.

R.9. All I ever get are bright metallic effects. How do I get more
colorful glaze effects?

This is the exact opposite of the previous question and problem.
Brighter colors need a degree of post firing oxidation in order to
develop. There are several ways to achieve this. When you remove
the ware from the kiln, spray the areas with water where you would
like more color to develop before placing the ware in the
reduction container. This will oxidize and cool the glaze. Another
method is to hold the ware in the air for 10 - 30 seconds before
reducing the ware. Allow the combustable material to ignite and
cover the container only after flames have clearly developed.
Other potters will uncover the reduction container after a short
time allowing the material to ignite again while fanning the ware.
Using these and other similar techniques you will learn how to
control the amount of metallic and colorful effects on your wares
as well as grey to black unglazed areas.

R.10. Can I preheat my pots in the kiln as it is warming up
(starting with a cold kiln). I will be using a fiber garbage can
kiln with a lift-off lid, not one where the entire kiln lifts
off.I don't see how my pots will get preheated enough by just
setting them on the lid. Do they get hot enough on a
fiber/expanded metal lid?

This question shows a common misunderstanding about the raku
process. The only time you need to be concerned about preheating
your ware is when you are doing multiple firing loads in the same
kiln. The first load should always be in a cold kiln taking the
temperature up slowly. Only if you are going to fire additional
loads should you be preheating your pots on or alongside the kiln.
If the lid of the kiln is a wire mesh/fiber lid then you might get
enough radiant heat. Place the pots near the flue opening so they
get the heat coming from the draft. Be careful not to place them
too close, too soon, or they may break. After preheating on top of
the kiln you can place the pieces around the base of the kiln
after you remove the fiber chamber, let them heat up there for a
minute or two, then put them on the kiln shelf letting them sit
for another minute, then put the chamber back in place for a
minute, then relight the burner.

R.11. Must I use a certain type of kiln or can I fire raku in an
electric
kiln?

Most any type of kiln can be used for raku as long as it meets
certain requirements of the raku process. It must be located
outdoors or in close proximity to the outdoors. You must be able
to easily reach into the kiln to remove your ware. If you are
going to be firing multiple loads the temperature of the kiln must
be easily controlled. An electric kiln is perfectly suitable for
raku although there are some special considerations that require
careful attention. You must remember that you are exposing
yourself to live electrical current when you open an electric kiln
so you must protect yourself from any possible contact with the
current. There'll be more on this in a subsequent
revision of this FAQ.

R. 12. When it comes to kilns I've heard the terms flue, damper,
stack, and chimney. How do they apply to raku kilns?

All fuel fired kilns need some way for the gases to exit, the air
flow to be controlled, and air to enter the chamber. Conventional
kilns have a flue, damper, and stack (or chimney). The flue is a
path in the kiln for the gases to move through after they have
circulated through the kiln on their way to the stack. The damper
is a device, usually a kiln shelf, that slides in and out of the
lower part of the stack in order to control the size of the
opening, thus controlling the exit of the gases and their mixture
with air. Raku kilns are generally small and overpowered. Most
have a simple opening in the top of the chamber covered by a kiln
shelf shard. The kiln chamber chamber is essentially the stack
with the opening the flue and the kiln shelf the damper.

R. 13. Why can't I reach temperature no matter how much gas I use?

This is the most common question regarding the raku firing.
Successful rise of temperature in any fuel-fired kiln depends on
the correct mixture of air and fuel. A hotter kiln is not
necessarily dependent on more fuel! If there is too much fuel, the
atmosphere will be smoky, full of flames and the temperature will
not rise. Also, if there is too much air, the temperature will
stagnate or fall. Usually, the solution to a situation in which
the kiln doesn't reach temperature is to increase the air in the
air/fuel mixture. In a gas-fired kiln this can be done by
increasing the available air in the burner or around the burner.
You can also simply open the flue (the opening at the top of the
kiln). Most potters use a venturi type burner that has a disk that
screws open or closed. Open it for more air. If you are using a
power burner in which a fan is attached, increase the air flow.
Experiment to arrive at the correct mixture but be patient!

R.14. Don't the tongs used to lift the pots leave marks?

Sometimes they do. More often though the glaze is still molten
enough that once the pot is released from the tongs, the marks
tend to smooth out. In either case the tong marks should not be
treated as defects but rather as characteristics of raku.

R.15. I'm confused about the term "reduction". Can you explain
what this means?

Reduction is a firing term that refers to a lack of oxygen in the
combustion process. This lack of oxygen in the atmosphere causes
the fuel to search for oxygen elsewhere to allow for more complete
combustion to take place. This can take place during a firing as
in "reduction stoneware". In this conventional situation, the
additional oxygen is found chemically bound in the the clay body
and glazes. The result is characteristic reduction effects.
Reduction as it is referred to in raku usually takes place out of
the kiln separate from the actual firing as described earlier.
However, just because you are doing raku doesn't mean that you
can't experiment with actual reduction firing in the more
conventional sense.

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?

As described earlier, post firing reduction is normally done by
removing the ware from the kiln and placing it in a container with
your combustable material. Certain situations may make it
difficult to actually remove the wares from the kiln while they
are hot. For instance your piece may be too large or awkward to
handle. In this case you can achieve some post firing success by
shutting off the kiln, adding your reduction material to the
chamber, and closing off all open ports including the flue, peep
hole, and burner ports. At best, the chamber will be only
marginally sealed, and since effective reduction depends on on an
airtight chamber, your reduction will be only partially
successful. If your kiln is a lift-off fiber type then you might
try removing it and replacing it with a metal drum or can for the
reduction phase.

R.17. Do different types of reduction material give different
effects?

The short answer is yes. The long answer is much more complicated!
Here is a medium answer: Your reduction effects are certainly
influenced by how much carbon is in the atmosphere that surrounds
your pot. In other words, how much smoke your pot is quickly
subjected to. Some materials have the potential to release more
carbon than others. The condition of your material (wet, damp,
dry) as well as the particle size as in the case of wood materials
(sawdust, shavings, chips) can be important. The type of wood can
also affect your results.

R.18. Must there be clouds of smoke when doing raku?

Raku doesn't require smoke at all. There are two aspects of the
process that have the potential for creating smoke. If you are
using a fuel fired kiln (as opposed to an electric kiln) then it
is likely that there will be at least some smoke generated during
the firing. If you are doing post firing reduction, there will be
smoke created then as well. The amount of smoke is determined by
the efficiency of your reduction technique, the material you are
using, and the amount of material you are using. If you are
reducing in a container, the tighter the lid fits, the less smoke
will exit the container. There are other techniques of reduction
that create less smoke than others. Of course if you are not doing
post firing reduction and simply cooling your ware when it comes
from the kiln, then there is no smoke created.

R.19. What is "smokeless raku"?

"Smokeless raku" is not really smokeless at all. The term was
coined by Jerry Caplan who has been developing his techniques for
many years. It is a post firing reduction technique that is
designed to produce minimal smoke by keeping the reduction chamber
as airtight as possible. This can be done using a combination of
tight fitting lids with "gaskets" of wet paper or cloth. The
tightest chamber is one made by inverting your container onto a
bed of sand or dirt. Arrange a ring of sand or dirt on the ground
for the lid of your container to fit onto when placed upside down.
Place your reduction material within the ring. Quickly place your
ware onto the material and cover it with the container pushing the
rim of the container into the sand. Bury the rim with additional
sand to keep the smoke in.

R.20. What is meant by "slip resist" in raku?

"Slip resist" refers to a variety of techniques whereby a clay
slip is applied to the surface of the ware. This slip is
formulated to peel away during the firing, and not permanently
adhere to the surface. As the slip peels, shrinks, and separates
from the surface it exposes the ware to varying degrees of post
firing reduction. When the piece is cooled, whatever slip remains
on the pot is removed by scraping and cleaning. As a further
decorative process, you can scratch and draw through the slip
creating designs.

For a complete handbook covering everything you need to know about
the practice of raku see the book "Raku: A Practical Approach" by
Steven Branfman, the author of this FAQ. The book is available at
your favorite book store, pottery supplier, or ou can order
directly from Steven's studio, The Potters Shop. Phone: 781/449
7687.

Compiled and first posted June 1996. Revised 5/99. Last posted
5/20/00
copyright Steven Branfman. All rights reserved.
please refrain from making any copy without permission.


Note: Today (Jul 19, 2003) Steve Branfman, away from his home base,
asked me to post his FAQs on raku methods. The version here was one
posted some time ago, and one that now has been somewhat revised by
Steven. The data posted above is essentially the key portions of
his revised version.

Tom Buck aa563 at hwcn.org) -- primary address. Tom.Buck at hwcn.org
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada

Ads
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Charter & (pointer to) FAQs RCG.FAQ.BOT Glass 0 August 16th 04 05:21 AM
Charter & (pointer to) FAQs RCG.FAQ.BOT Glass 0 July 16th 04 05:21 AM
Charter & (pointer to) FAQs RCG.FAQ.BOT Glass 0 July 1st 04 05:21 AM
Charter & (pointer to) FAQs Steve Ackman Glass 0 June 16th 04 05:21 AM
FAQ:Intro to rec.crafts.pottery Mishy Lowe Pottery 0 July 18th 03 06:05 AM


All times are GMT +1. The time now is 04:08 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 CraftBanter.
The comments are property of their posters.