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In This Issue
* While the Smoke Clears
* Fading Glazes Feedback
* Getting "that" Copper Matte Color
* Paragon Kiln FAQ Document
* Naked Raku Pictures
* Vanadium Stain vs. Vanadium Pentoxide
* Lasting Kiln Shelves
* Raku Web Links
* Workshops, etc.
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* While the Smoke Clears * Yeah, I know. It's not May any more. Yes, this newsletter is WAY late, but I figure better late than never, right? I've changed the format of the newsletter a little bit, which I think will help me get the issues out a little easier and faster. Plus you should be able to tell what's in each issue a little easier as well. Let me know what you think. One thing I wanted to make sure and tell you is CafePress is having a sale. You get $10 off any order of $30 or more until Jun 14, 2005. So hurry! Just use coupon code GRDAD05 (that is a zero-five) during checkout at any of my stores: Just Raku Logowear http://www.cafepress.com/justraku
Got Raku http://www.cafepress.com/gotraku
Raku Secrets http://www.cafepress.com/rakusecrets I appreciate your support - plus you get to save some coin. As always, I look forward to your feedback, suggestions, questions, and article ideas at:
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Gary R. Ferguson
- Raku Artist -
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Here is an easy (and free) way to support this newsletter. Open a new eBay account by clicking on the link below and select "register" at the top of the screen. Then look for a deal and bid. Your support is greatly appreciated! http://www.qksrv.net/click-411938-2202639
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~~-~-~-~-~-~-~-~-~- * Fading Glazes Feedback * Chris R. had the following feedback on the issue of fading colors of some Raku Glazes.
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Tom Buck in Ceramic Review Issue #159, May/June 1996, on which the following is based, discussed the question of "fading" glazes in an article. The rainbow colors on a copper-matt pot are caused by firstly reducing the metal oxides in the glaze back to metal and, secondly, allowing that shiny metal surface to oxidize slightly, which produces the light interference that gives us the color effect we seek. If the exposed metal surface is not protected, then it will be subject to further oxidation - in the case of copper, it may even oxidize all the way back to black copper oxide, as your contributor has seen. In other Raku glazes, the overall result is a porous ultra-thin layer of colored glass on or near the glaze surface whose complexes are open to attack by airborne oxygen, moisture, and sulfur compounds. Put simply, the reduced glaze is too porous and/or too easily affected by the environment. The original Raku glaze cut-and-try approach led to this problem, since good glass does not come from impure calcium borate (Colemanite/ Gerstley borate) and/or hydrated sodium borate (borax). Neither one of these borate materials by itself, nor any combination of the two together, will form a long-lasting surface. Also, it takes more than 20% Nepheline Syenite to provide enough silica and Alumina to make the glaze durable. A look at the Seger formulas for most Raku glazes shows why they may change. They often lack sufficient silica (quartz, flint or, chemically, silicon oxide, SiO2) to form a durable glass. Many are also deficient in alumina (aluminum oxide, Al2O3), which toughens glass and helps to seal the glass surface. Even Branfman's book http://www.garyrferguson.com/branfman gives the same "80/20" borate glaze recipes of the 1960s (with minor changes) although, to his credit, he also lists newer balanced glazes that use frits in their mix (both borate and alkaline frits). So what is the answer to the fading problem? Seal the glaze, either by using a varnish of some sort (but keep it out of sunlight) or by making the glaze a viable glass by a combination of intelligent alteration of the glaze chemistry and LOTS of testing. Glaze chemistry is fascinating and, once the initial concepts are grasped, not too difficult to understand. Learn about it now. You'll have to when the Gerstley Borate runs out anyway!
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So it really boils down to the fact a copper matte glaze is not "glass" enough to maintain the colors for extended periods of time.
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~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ * Getting That Copper Matte Color * How do I get "that" copper matte color! I get this question all the time, like the following:
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I live in Portland and went to the big Ceramic show last weekend at the Expo Center. I was checking out this Raku booth and I really liked the glaze they used. I asked them what is was, and he said it was copper sand with some or all of the cobalt taken out and more copper added. I'd love to get that recipe. I'm sending you a few pics of another local artist who does the exact same glaze. It has lots of magentas and purples and blues, and isn't glossy - more like satin. Maybe you can tell me what it is if you recognize it. I know they reduce in pine needles, which I can't find any right now. Hope you can help me. Thanks in advance!
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Unfortunately, I'm never much help in these cases because one thing I have learned about Copper Matte glazes, is it is not so much the glaze formula as it is the application, the firing process, and/or the reduction technique. The exact same glaze can look wildly different depending on the thickness of the glaze application, how it is fired, and how it is reduced. Even if you knew all these, you will likely still not get the same result every time. No potter ever does. So my recommendation is to try a couple of glazes either from my website (http://www.garyrferguson.com/rakuglaz.htm) or my ebook ( http://www.rakuglazes.com) with various techniques and see what you get and take good notes as to what you do which may help you with future firings. ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Raku: A Practical Approach by Steven Branfman
The "nuts and bolts" how-to book of Raku
Order 30% off at: http://www.garyrferguson.com/branfman
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ * Paragon FAQ Document * Paragon has a 71-page Microsoft Word document of frequently asked questions (FAQ) on electric kilns. There appears to be many other useful documents on this site as well.
http://www.paragonweb.com/catalog.cfm?type=manuals ~~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-
Amazon sells more than books! Help support this newsletter by using the following link: http://www.garyrferguson.com/amazon
~~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- * Naked Raku Pictures * Here are some wonderful pictures of Naked Raku, both the process and the finished product.
http://www.fromthepines.net/wally/ ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
"It's all your fault.......I was up all night reading "Raku Secrets". I have been Rakuing for about ten years, and still so much to learn. Your Raku Secrets gave me a lot of new insight. Thanks so much". - Elaine S.
http://www.rakusecrets.com
~~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ * Vanadium Stain vs. Vanadium Pentoxide * I've had some question to the reference to Vanadium Stain for the Yellow Crackle on my website and whether this is the same as Vanadium Pentoxide. The recipe is as follows: Yellow crackle Gerstley Borate 80
Cornwall stone 20
Vanadium stain 3-6 I do believe Vanadium Stain is different that Vanadium Pentoxide. They are listed as different chemicals for example on the following pottery supply website:
http://www.milehiceramics.com/glaze_chemical_prices.htm The formula for Vanadium Pentoxide is V2O5 and the Vanadium Stain is a Mason stain that is a combination of Vanadium Pentoxide and Tin. So I would assume you could use Vanadium Pentoxide and some Tin Oxide in place of Vanadium Stain. Heck, it is Raku - give it a shot! ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Raku Pottery by Robert Piepenburg
The must have "Bible" of Raku
Order at: http://www.garyrferguson.com/piepenburg
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ * Lasting Kiln Shelves * One reader wrote: How long do your kiln shelves last? I'm finding they crack after about 10 firings. I've tried both full and half shelves, same problem. Do you bisque fire them in an electric kiln before using them in the Raku kiln? How far up from the floor are they set? My torch enters from the side (not bottom) and I'm using four 6" posts. Do you use soft brick as shelf support? Any advice to cut down on breakage would be most appreciated.
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Well, I've been using the same kiln shelf for 3 or 4 years now. It's not real big, about 12 inches across and I set it on 3 pieces of soft brick. My burner comes in the side below this shelf. The soft bricks have broken and crumbled over time and have been replaced, but I never had a problem with the shelf. I do set all my pieces on stilts and not directly on the shelf, which is probably a benefit. I also take about one hour to fire to temperature. If you fire extremely fast I could see this as a potential problem as well. ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Alternative Kilns & Firing Techniques - James C. Watkins, Paul Wandless http://tinyurl.com/72aaf
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ * Click Away * My eBay Listings http://tinyurl.com/tn08
Just Raku Blog http://justraku.blogspot.com
Just Raku Logowear http://www.cafepress.com/justraku
Got Raku? http://www.cafepress.com/gotraku
Just Raku Archive http://www.JustRaku.com
Fact Hive http://www.facthive.com ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Raku - John Mathieson http://tinyurl.com/3f5yh
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Raku: Investigations Into Fire by David Jones
Order 30% off at: http://tinyurl.com/8m5x
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