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FAQ Raku part 1 of 2



 
 
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Old September 16th 03, 11:10 PM
SBRANFPOTS
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Default FAQ Raku part 1 of 2

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
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