Judy Rohrbaugh on sun 30 oct 05
I just started testing a few glazes in my raku kiln. Think I am pulling the tests out before they are matured.
I pulled a few out when the glazes were bubbled looking, somewhat shiny.
However, one glaze flaked off the test piece, and the others are not smooth, bubbly, lumpy looking.
What specifically should I look for in the tests to know the glaze has matured and is ready to take from the kiln?
A good thing, they are reducing fine, and the colors of the glazes look good, but I am assuming that I'm not going hot enough.
Also, should I put raku glazes on the usual thickness as in cone 6 work? I may be putting the glaze on too thickly?
Thanks,
Judy Rohrbaugh
Fine Art Stoneware
Ohio
jrohrbaugh@sbcglobal.net
Craig Clark on sun 30 oct 05
>What specifically should I look for in the tests to know the glaze has matured and is ready to take from the kiln?
>
>
>
Judy, if you are dealing with glossy style raku glazes then be sure
to wait until "the bubbles" are no longer visible on the pot before you
pull it from the kiln. The time it takes you to get to this point will
vary depending upon the glaze itself, application of the glaze, type
kiln you are firing the pots in, the rate at which you are firing up the
kiln, etc..
If you are getting the colors that you want then you are most
probably getting close to the maturation point of the glaze. You'll just
need to leave them in a bit longer and look into the kiln carefully when
you think that you are near where you need to be. As you gain experience
you'll develp a feel for things. You will be able to look at the color
of the atmoshpere in the kiln and make a pretty good guess. Try looking
at the side silhoutte of one of the pots and look for a reflection. Once
you can see this then the glaze has fused and the pot may be removed.
Additionally, you might consider investing in, if you don't already have
one, a pyrometer and get an idea of the ambient temp at which you pull
your pots as well. While this doesn't tell you anything about the work
heat it does give you a good indication of where you are in the realm of
Raku. You can pretty much run things free and loose as long as you are
getting the results that you are after.
One thing that I always recommend is for folks who are new to the
process to go out to the Digital Fire websight and read Tom Bucks's
article on raku glazes. Many of the glazes used in raku are not stable,
are photo reactive and will fade with time. He explains what occurs as
well as offering up glazes that are more permanent than many of those
that are frequently used.
As always, the comments, recommendations, etc., are not meant to be
definitve nor are they the only way to do things. These are just things
that work well for me.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
John Jensen on sun 30 oct 05
The way I learned is: When the surface begins to look like ice with a thin
water coat...like just melting ice. Look close to an edge so that you are
not seeing the glaze straight on, but at a fairly extreme angle. Make
sense?
John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com
Leland Hall on mon 31 oct 05
On Sun, 30 Oct 2005 14:16:24 -0800, Judy Rohrbaugh
wrote:
>I just started testing a few glazes in my raku kiln. Think I am pulling
the tests out before they are matured.
> I pulled a few out when the glazes were bubbled looking, somewhat shiny.
>However, one glaze flaked off the test piece, and the others are not
smooth, bubbly, lumpy looking.
>
>What specifically should I look for in the tests to know the glaze has
matured and is ready to take from the kiln?
>
>A good thing, they are reducing fine, and the colors of the glazes look
good, but I am assuming that I'm not going hot enough.
>Also, should I put raku glazes on the usual thickness as in cone 6 work? I
may be putting the glaze on too thickly?
>
>Thanks,
>
>Judy Rohrbaugh
>Fine Art Stoneware
>Ohio
>jrohrbaugh@sbcglobal.net
>
Many good tips have been offered, and I agree with all. To add I would
suggest perhaps that a soak at whatever temp is appropriate can often
aleviate bubble and pinhole problems. When things get to be melting good,
turn down the gas a bit let the kiln coast. It took me while to to find
this out, and when I did things started looking much better, especially the
glossy raku glazes.
Best of luck and have fun
Leland Hall
Before The Wheel Enterprises
La Pine, OR USA
Paul Gerhold on mon 31 oct 05
Judy,
My wife and I do very precise Raku with tape designs so pulling the pots at
the correct time is critical for our work. What we do is actually put large
cones in with the work and then use them to tell us when to pull the pots.
Once you figure what cone works for your glazes you can achieve very
reproduceable results. Using cones really reduces the tendency to pull pots too early
which seems to be our natural behavior.
As for glaze thickness I find that most Raku glazes work best when applied
much thicker than cone 6 glazes.
Paul
William & Susan Schran User on tue 1 nov 05
On 10/30/05 5:16 PM, "Judy Rohrbaugh" wrote:
> What specifically should I look for in the tests to know the glaze has matured
> and is ready to take from the kiln?
The glaze should appear smooth, shiny, glossy, wet, mirror like finish.
If you are able to view the glaze from more than one angle, that might be
helpful. Also firing at night will often allow you to see the glaze surface
better.
I'd also suggest the clay surface be smooth to which you apply the glaze.
It's often more difficult to see proper glaze melt on a textured surface.
>Also, should I put raku glazes on the usual thickness as in cone 6 work? I may
>be putting the glaze on too thickly?
Depends on the specific glaze. A white glaze we use works best at a "normal"
thickness, while an "alligator mat" works best very thin.
I'd start with your "cone 6 thickness" and run tests thicker and thinner
until you find what you want.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Marcia Selsor on tue 1 nov 05
> On 10/30/05 5:16 PM, "Judy Rohrbaugh"
> wrote:
>>> What specifically should I look for in the tests to know the
>>> glaze has matured
>>> and is ready to take from the kiln?
>>>
>>
>>> Also, should I put raku glazes on the usual thickness as in cone
>>> 6 work? I may
>>> be putting the glaze on too thickly?
If you dip, let the glaze dry out a day or be sure to pre heat them
well enough to dry out.
I think the same as ^6 works for the lusters and crackles. I spray
the matts. Thick will develop an alligator texture. Thinner gives me
the color variations I want. Bill gives good advice for your
questions. I use matt glazes and need to use a pyrometer because
visual observation doesn't work for them. I fire to 1850 F on my
pyrometer for the results I wants.Otherwise, if using a luster or
crackle raku glaze, watch it. It will bubble up like pancakes before
you flip them. Them is smooths out to be shiney gloss. Then pull them
out.
Best wishes,
Marcia
back home in Montana
denny means on wed 2 nov 05
Judy,
Welcome to the Raku world. I have seen a couple good responses to your
question and I will try not to duplicate what has been said on the topic.
A mature glaze in Raku will have "the look of melted water on top of a
sheet of ice." That description was not originated by me, but it stuck in
my head and serves as a good guide. Glazes showing a bubbled surface are
not mature - the glaze will smooth out when it is fully melted.
In my experience, the temperature at maturity of many Raku glaze recipes
will vary widely. Meaning some glaze recipes will mature at 1700 degrees or
so, other recipes have to be fired to 1850 degrees or higher. I have not
had good results firing a higher temperature raku recipe to only 1700
degrees.
Thus, it is good to pay careful attention to any remarks made with the
glaze recipe to get an idea of the target temperature range. One of my
goals is to fire only glazes with similar maturity temperatures in a kiln
load.
Take a look at Steven Branfman's excellent book, "Raku - A Practical
Approach" which can be ordered from the Potter's Shop. This book has many
glaze recipes in it and discusses the maturity temperatures.
I also suggest investing in a pyrometer. Your understanding of your kiln
and what is going on inside the kiln will grow by leaps and bounds with a
pyrometer installed. Various supply houses carry pyrometers, and Axner's
sells a cheap one.
You may also want to take a look at the (free) Raku Workshop Manual that is
on my website. The manual is a compilation of tips on making pots for raku
firing and has a section on glazes and glazing. It will help you on the
path.
Good luck with your work in raku.
Denny Means
Mason, Ohio
http://home.earthlink.net/~crookedtreepots/
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