Greens

GLAZE OF THE WEEK 8

SHALL WE TALK ABOUT THE GREENS?

HPG has several choices of green glazes with greatly different appearances in the final firing depending upon the type of clay and the conditions of firing.

ORIBE is a very glossy, bright green glaze usually used as an accent glaze near the top of the pot because it tends to run considerably. It is effective when used on top of clear Chun or Nelson’s with just about any clay body. On top of Miller White it tends to pale out to a soft green. It does not change color very much with darker clays. If used by itself on porcelain, it must be very even, thin and high off the bottom of the pot. Careful application can produce emerald green on porcelain.

LIMESTONE GREEN is an older glaze which has a nice break from a rather gray green clear look where quite thin to an white opalescent look where thicker, partly because of the borates in the formula. It tends to run. Its use has been discontinuted because a small perecent of Barium is unsafe at HPG. (see Ch. 11)

REITZ GREEN is an excellent, stable, non-runny glaze which comes out a semi matte dark jade green with black markings. When it is applied evenly with normal thickness, the jade green dominates. Where thin, it is black. On white clay it maintains a clear jade color, on dark clay it is darker with some speckling.

JOE’S GREEN has become very popular because it is so interesting. It is best on dark clay when the soft medium green due to its copper content shows on the surface with some dark speckles from the clay. Sometimes the green color meshes with some brown undertones. The semi matte finish is very handsome. It is essential that this glaze be very thin in the bucket, as thin as skim milk, and it needs to be thinly applied to the pot. No double dipping with this glaze, in fact wiping off the thick or drip areas might be a good idea. Where thin, it fires green; where thicker it is black. This is exactly the opposite of Reitz Green. Joe’s green is very stable, does not run. Queenie Kwock and Esther Nowell have had excellent results on their pieces, using this glaze on either functional ware or on sculptural pieces. On porcelain the effect is not the same green, but much lighter, and sometimes gray-green with some pinkish flashes which could be attractive on a heavily carved piece.

MacKENZIE CELADON is a clear kaki glaze which is good on any clay body and which not run. On white clay it usually appears as clear, dark yellow green especially in reduction. In oxidation it may not be clear. On dark clay it is clear but darker and speckled. Accents with other glazes on MacKenzie Celadon work well: Tenmoku designs, trails of UH Blue, one of the reds......who knows?

ETSUKO’S GREEN is her own concoction of a “pinch” of chrome oxide mixed with a jar of one of the clear glazes, half Nelson’s Transparent, half Chun. It can vary from bright apple green at times, to a nice soft clear light green. Too much chrome oxide turns the glaze to brown. Experiments need to be done to quantify the exact proportions of chrome to glaze which is about 0.125% for a consistent formula. It can be used the same as the other transparent glazes with more assurance that a true celadon will

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result. Mahalo to Etsuko Douglass for sharing her glaze. Now it is up to the glaze committee to experiment with it. There are at times three buckets of this green, each one a different shade. Etsuko Green is the lightest. “Apple Green” is a bit more intense green, and “Sour Apple Green” is very bright green like a Granny apple. These greens are a result of experimental “pinches” of Chrome Oxide. However, to avoid so much variation, this glaze is now made up by starting from “scratch”. Making dry batches of Nelson’s Transparent and Chun together with a final percentage of 0.125% Chrome Oxide does the trick making a soft fool-proof celadon glaze.

CHUN GREEN is just that: Chun with Chrome Oxide in it. How much? Again, it is just a “pinch”. This can mean no more than 0.05 %. The result is a delicate green on white clay, especially Coleman porcelain.

PRIMAVERA GREEN means “Spring green” and it is just that: a lovely, bright clear apple green, surely best on white clay. Anushka Faucci formulated this.

HENDERSON’S TURQUOISE is another accent glaze, semi matte bright turquoise green like the gemstone. It may not not interesting if used on the whole pot, but very attractive if used sparingly on almost any other glaze as an accent. It is especially good on dark glazes such as G Black, Tenmoku, or Rachel’s Black.

STAINS AND OXIDES of certain minerals are green if applied as a wash wiped onto the piece whether left unglazed or overglazed with a transparent glaze. Copper carbonate can be strong green with a slight bluish cast. Chrome oxide is usually much stronger, an acidic green when fired. These oxides can be hard to control. Ceramic stains are formulated with combinations of minerals which produce consistent color. Peacock Blue/Green Ceramic Stain is mixed as a powder into porcelain slip the consistency of half and half cream. This mixture is “painted” onto a piece in a design or to cover the whole pot at the greenware stage. It is bisqued then a transparent glaze is used over this. The result is a rich dark blue green. Pat Harwood often uses black ceramic stain, mazarin blue, and peacock blue. Currently stains, which are expensive, are not furnished by HPG, but are available by the ounce at Ceramics Hawaii.

TURQUOISE BLUE MATTE is a popular new glaze. On a small test tile porcelain shows a strong blue green; iron rich darker clay shows a darker more green blue. Both are brown-black where thicker with a non shiny matte finish, but not chalky. This glaze will make lovely gemstone accents on clay. Experimentation will reveal how it works on top of other glazes, on Shino and on Chun it has not been a good accent. By itself on a small piece it is beautiful. On Letty Geschwind’s large carved pieces using dark clay, this glaze was rubbed on with handsome effect after firing. It has been stable unless applied too heavily and fired too hot. See Patti Gallagher’s carved plates for stunning results. When diluted with Mamo, a soft light stable green is formed.

ANTIQUE GREEN is a formula from John Britt. In our firings this glaze is very beautiful, a rich Oribe-like green with royal blue where it breaks. It is not stable in our firings., probably needs cone 9. Best used at the very top of a pot. It does not look very antique at all, and not with grays as pictured in Britt’’s book: High Fire Glazes.

Pat Harwood 6/3/2005 ed January 2009 Ed. April 23, 2009; Nov 2010

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