- Newsletter - 

The Newsletter for Raku Artists and Raku Art Lovers
September 2003
Issue #12
Published by
Gary R. Ferguson - Raku Artist

In This Issue
* While the Smoke Clears - Poll Results & PMI Article
* From The Studio - Glaze Testing & Commission Work
* Article - Glaze Testing (Part I) - Mixing
* Tips/Techniques - Glaze Testing Containers
* Q&A - Underglazes and Reduction
* Glazing - Turquoise
* Bookworm - Magazine: Clay Times
* Reader Feedback - You said it
* Calendar - Where's Gary?
* Click Away - More Glazing Info Sites

* While the Smoke Clears *

According to the results of the last month's poll many of you would be interested in buying some premixed Raku glazes. I will work on creating a price list for some of my favorites and let you know when they are available. Thanks for your feedback.

If you are a subscriber to PMI (Pottery Making Illustrated), which I reviewed last month, be on the lookout for an article that will include my website. The article is supposed to be about on-line resources for potters so I'm quite pleased to be included in this magazine.
Remember I always look forward to your feedback, suggestions, questions, and article ideas at:

Gary R. Ferguson
- Raku Artist -


Would you like $25 in free books at Sign up for the no annual fee Platinum Visa from Bank One at

* From the Studio *

This was a busy month. I participated in an Art show the beginning of the month. It was not the most successfully show I've done, but I had an opportunity to meet and talk with several other potters and made some potentially beneficial contacts. I guess it goes to show that even a "bad" show can turn out good.

I researched and tested several glazes in preparation of completing the commission pieces that I have been working on the last several weeks. I got some good results, some bad results, and some results that I need to do some more testing. One of the "good" results is the Glaze of the Month below.



* Article *

Glaze Testing (Part I) Mixing

In testing glazes, there are two basic types of glaze testing that one can focus: color results and surface texture results.

Surface texture deals with whether the glaze is matte or glossy, stable or runny, textured or smooth, crazes or fits the clay body, etc. I generally do not modify and test glazes in an attempt to affect texture. I am generally more interested in taking a glaze that already has the texture I want and modifying the color results.

One element that can affect color results is the percentage of colorant that is added to the base ingredients of a glaze. For example 3% of copper carbonate (colorant) added to a base glaze may produce turquoise, 6% may produce a dark green, and 15% by produce almost black.

Modifying a glaze by adjusting the colorant percentage is relatively easy. You could mix several 100 gram batches and add a different percentage of colorant to each batch and then glaze a piece or a section of a piece with each test batch. This method is effective but not very efficient. You end up with several 100-gram batches of glaze that you only use a few test grams and then potentially throw it away.

A method I used recently is the glaze, add, and repeat method (much like the lather, rinse, and repeat on a shampoo bottle). Using this method you mix a 100-gram batch of the base glaze and then measure out several small amounts of colorant - such as four 2-gram quantities of copper carbonate. These can rest on just a small sheet of paper until needed.

Then you add water to the base glaze, glaze a test piece or a portion of a test piece, and then add one of the quantities of colorant. Using the above example, this creates a batch with about 2% copper carbonate (actually slightly more because some of the 100 gram batch was already used on the piece). This new batch is then applied to another test piece or section of a test piece. A second quantity (2 more grams) of copper carbonate is added to the batch. This results in a batch with approximately 4% copper carbonate (again slight more than 4% because more of the batch has been used). This process is repeated until each of the quantities of colorant have been added, and a test piece or section of a test piece has been glazed.

This method will not provide you an exact result for a recipe, but it should give you a good idea of what combinations or ranges should be focused on for a larger test batch. For example, if in the case above the 4% batch produces a pretty nice glaze, you may want to mix up 2 new 100-gram test batches - one with 3% colorant and the other with 5% colorant. This second test method will produce much more accurate results than the first method, but the first test method quickly narrows down what percentage range of colorant should be investigated using the second method of testing.

This method works well when adding stains to a glaze as well. The effect of a stain in glaze can vary greatly (1% to 40%) from stain to stain, and base glaze to base glaze. You would not want to waste expensive stains in a dozen 100 gram batches when one 100-gram batch with repeatedly adding additional stain and glazing can quickly and economically test stain percentage ranges.

Next Issue I will cover how to efficiently glaze and fire the test batches.

Raku: A Practical Approach by Steven Branfman
An excellent how-to book of Raku
Order 30% off at:

* Tips and Techniques *

Glaze Testing Containers

Plastic pint freezer containers make great containers for small test batches of glaze. They are relative inexpensive, durable, reuseable, and almost airtight. A pint container will hold about a 100 to 200 gram batch of glaze and the needed quantity of water.

The dry ingredients and water can be added to the container and with the lid replaced and carefully sealed the contents can be quickly mixed by just shaking the container for a few seconds.

The lidded container can be used to store a mixed batch of glaze over a good period of time.

Find New, Used, and Bargain Raku Pottery, Books, Videos, and Equipment on the largest auction site on the Internet - eBay - Join today!

* Q & A *

Q: In this most recent newsletter, you mentioned underglazes. Would you be kind enough to tell me if the reduction process complete with garbage can and
combustibles preserve the underglaze colors.

A: Typically the reduction process, especially if used under a clear glaze does not affect underglazes. They are probably more affect by the influence of the ingredients of the covering glaze

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* Glazing *


100 - Frit 3110
3 - Tin Oxide
3 - Bentonite
3 - Copper Carbonate

This is a very simple basic glaze that can produce a wonderful turquoise crackle. The glaze should be applied fairly thick. It will be yellowish where thin. The maturity temperature is around 1800F. The piece should be very lightly reduced to obtain the turquoise color. I remove the piece from the kiln and then hold it in the air for 20 to 30 seconds before I place it in the reduction chamber. If the piece is quickly or heavily reduced, more copper and darker greens will result. The glaze generally produces a crackle pattern and an orange peel (or micro bubbly) texture where really thick.

If no copper carbonate is added, the glaze is a nice white crackle. If 6%+ of copper carbonate is used, the turquoise color becomes a forest green. It's almost like getting three glazes for the price of only one recipe.



* Bookworm *

Magazine: Clay Times

Last month I covered the clay magazine Potter Making Illustrated ( Another magazine I subscribe to is Clay Times: The Journal of Ceramic Trends and Techniques. This is another magazine that focuses more on the "how to" of clay. There is always something of interest in each issue. Whether it's a business article of how to sell more art, new glaze recipes, new firing techniques, new construction techniques, or an inspiring picture in the reader submitted gallery section.

A sample of recent articles include: Throwing Large Forms, Build Your Own Spray Booth, Increasing Your Claywork Sales, Naked Raku-Flemish Style, and a Val Cushing Workshop.

The publication is produced six times a year and can be subscribed to a:

Raku Pottery by Robert Piepenburg
The "Bible" of Raku
Order at:

* Reader Feedback *

The following are some excerpts of the feedback last month.

* * *
Adding to the info on the underglazes and Raku article. I have used them [underglazes] on a large mosaic with nice (I think!) results. The Underglazes were used when the clay was leather hard and then the piece was bisque fired. I used a clear Raku glaze with a dry brush technique and quickly applied the glaze over the piece in a pretty rough manner. The result after oxidation firing in an electric kiln was a variation of tonal qualities as areas having clear glaze were darker color than the areas, which didn't have the clear glaze. I used some inks to finish the piece to get into the cracks, as I just wanted to try the Raku glazes in an oxidized atmosphere....
Hope this is helpful......Janet

[Thanks for describing the technique you used]

* * *
Would love to hear about workshops, especially here in northern California.
Thanks, Sharon Zachary

[Ok readers, if you know of any Raku workshops, let me know and I'll include them in the newsletter. Remember the newsletter only comes out at the beginning of each month]

* * *
Hi Gary and all, I just wanted to let you all know how important this newsletter is to me. I am relatively new to pottery, and have fired Raku only a few times. Once at a class I was taking and once with my good friend Dave Garner from Turn and Burn Pottery in Seagrove, North Carolina. I have suffered a stroke and am disabled, so I practice throwing my pots when health permits. Some days I don't feel like even getting out of bed, but I am always inspired to go to my studio and throw some pots after reading the Just Raku Newsletter. Gary is so giving with his techniques and recipes. I am always inspired after reading the Newsletter. Keep up the good work Gary!
John in Saxapahaw, North Carolina

[Feedback like this will definitely keep to the newsletter going - Thanks John and hang in there!]

* * *
I also have a comment/suggestion. When I read your newsletter the text formatting is off. I'm wondering if you are using hard returns versus a wrap text function. I've tried resizing my browser with no improvement. (I have a very small screen). It looks like this to me when I read:
"This is what happens to the text when I
read the
newsletter each month. It is certainly readable
but it
is less than ideal. Hope this helps you!"
Thanks again for the newsletter. I particularly enjoy your section where you kind of trouble shoot something going on.

[Anyone else having problems. I create the newsletter in Word and cut and paste it into a plain text document in Outlook. I'm not using any hard returns that I know of, other than at the end of paragraphs.]


* Calendar *

My full calendar can be seen at:

Nov 1-2 Eagle Holiday Bazaar
Eagle High School, Eagle, ID

Nov 5-12 Beaux Arts Society Holiday Sale
Boise Art Museum, Boise, ID

* Click Away *

The Ceramics Today Update - Newsletter
Check out this free newsletter sent weekly to subscribers that presents articles, book reviews, the 'Pot of the Week', 'Website of the Week' and more. To subscribe simply go to:
Tell them, "Gary at Just Raku" sent you.

BigCeramicStore - Glaze Testing Article

Digital Fire - Glaze Temperature Adjustments

Claymaker - Glaze Defects

Just Raku Newsletter
The past issues can be found at

Raku: Investigations Into Fire by David Jones
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JUST RAKU (C) Copyright 2003, Gary R. Ferguson