- Ceramic Arts Daily - http://ceramicartsdaily.org -

Experiments in Peach Bloom: Extensive Testing Reveals Secrets of an Elusive Ceramic Glaze

Posted By John Britt On February 9, 2011 @ 9:07 am In Ceramic Glazes,Daily,Features | 19 Comments

Detail of a Peach Bloom glaze surface.

Peach Bloom glazes (aptly named since they look like ripening fruit) are some of the most delicate and beautiful glazes around, as you can see in the photo to the left. But they are also elusive -  the secrets of this glaze and firing technique have remained a mystery for centuries. So when potter John Britt was approached by Lindsey Elsey, a student who was looking for a research partner on a study of these glazes, he gladly signed on.

 

Six hundred test tiles later, John and Lindsey uncovered some of the secrets to developing gorgeous peach bloom surfaces. In this excerpt from the October 2010 issue of Ceramics Monthly, they share the results of their research, and a bunch of Peach Bloom glaze recipes. – Jennifer Harnetty, editor.

 


This article appeared in Ceramics Monthly magazine’s October 2010 issue. To get great content like this delivered right to your door, subscribe today!

Peach Bloom glazes were used in China during the Qing dynasty (1644–1911) to decorate objects for the emperor’s writing table, like water pots and ink wells, as well as decorative vases and bowls. In his definitive book Chinese Glazes, Nigel Wood lists many names for Peach Bloom glazes, like “apple red,” “bean red,” or “drunken beauty” for a category of glazes with various shades and a mottled surface, while “beauty’s blush,” “baby’s face,” and “peach blossom” are reserved for those with lighter tones. The number of names given to describe these glazes shows the wide variety in this magnificent glaze.

 

What is most intriguing is that the secrets of this glaze and firing technique have remained a mystery for centuries. However, at its core, Peach Bloom is a copper-based glaze that gives the impression of ripening fruit. So it may be a transparent green that blushes pink or a pinkish background with green or red speckling.

 

I have long been interested in this glaze but had never had an opportunity to pursue it fully. Then, Lindsey Elsey, a studio arts major at Appalachian State University in Boone, North Carolina, approached me with an interest in studying copper red glazes for her senior internship, which would end with her giving a presentation as well as an exhibition at the Crimson Laurel Gallery in Bakersville. She said that, for her, copper reds were the first truly satisfying glazes she experienced in her work. She felt that, beyond their vibrant color, successful copper reds embodied the idea that if everything came together just right—the clay body, the glaze mix, application, form, firing, and cooling—then magic could happen. Although she understood that struggling with so many variables could be a frustrating process, she believed that, in the end, producing one successful pot would be worth the entire struggle.

 

I suggested that rather than working with the entire category of copper reds, we focus on Peach Blooms, which are the most difficult to achieve. Since the project seemed interesting and challenging to both of us, we agreed to work together and began by designing a testing program.

 

 


 

Current Literature

 

We found very little written on the subject of Peach Blooms. However, several books did have small sections: Copper Red Glazes by Robert Tichane, Stoneware Glazes by Ian Currie, Chinese Glazes by Nigel Wood and my book, The Complete Guide to High-Fire Glaze: Glazing and Firing at Cone 10. While none of these books have a definitive method, from these sources we set up a group of tests to see if we could achieve something close to ancient Peach Blooms.

 



Testing Methods

 

  • Aging glazes to allow crystallization (Currie)
  • Spraying copper/tin over a celadon glaze (Britt)
  • Layering copper pigment and clear glaze (Wood)
  • Sprinkling black copper oxide over glazed pots, using coarse flaked copper oxide (Tichane)
  • Using Oribe glazes in oxidation firing (Britt)
  • Placing pieces in saggars coated with Oribe (Britt)
  • Underfiring (Britt)
  • Starting reduction later, around cone 011–08 (Britt)
  • Striking firing (Britt)

 

Due to time constraints, we knew we could not pursue all these methods, and we decided the most promising were strike firing (reduction period during the cooling) aging glazes (because I had five “old” buckets of copper reds) and sprinkling coarse copper oxide on wet glazes. While our main focus was on these avenues, we could also sample some of the other ideas without fully investigating them to see if there were some areas for future study.

 

We then set out to collect as many copper red recipes as we could, eventually ending up with 80 distinct recipes. As we collected recipes, we searched for as wide a variation as possible. That way, even if we did not find the perfect recipe, we would at least get something in the ball park that would hopefully lead us in the right direction. We made 600 tiles of Helios, a Grolleg porcelain, and also threw several dozen test pieces that we would use after the initial test firings. We then made 300 gram batches of each test glaze, dipping five tiles in each glaze. Each of these was then fired in one of five different firing cycles.

 


 

 


Firing Cycles

 

Strike Firing 1 (S1) oxidized to cone 10 (2345°F or 1285°C) in a gas kiln, cooled to 1550° F, then restarted and put into reduction (0.80 on the oxyprobe) for two hours, then shut off. Missing the initial glaze reduction period on the way up causes the glaze to seal over and then the striking (reduction period during the cooling) causes only the glaze surface to reduce to reds or spotty reds. The results from this firing cycle were so good that we did another (S2) to see if we could duplicate it, but this time with even heavier reduction.

 

Strike Firing 2 (S2) was similar to S1, but with slightly heavier reduction (0.85 on the oxyprobe). Some of the pieces in this cycle came out of the kiln too dark or a flat monochrome red. This was caused by excessive reduction and meant we needed to lighten up reduction for the next trial. But in order salvage the pieces we wanted to reintroduce the spots and blue-green color, so we put them into an electric bisque kiln firing and refired them to cone 06, this was basically an oxidation soak that re-oxidized some of the copper and caused the pieces to become more visually interesting.

 

We did another strike firing with a very a quick cool to 1550°F (843°C). This made no difference with our color but it did cause an interesting “earthworm” or “tear” mark effect. These appear to be cracks in the glaze or piece but, in fact, are the glaze surfaces cooling rapidly while the glaze under it is still molten, causing it to shift and tear.

 

Coarse copper oxide was also applied to some of the fresh raw glazed pots in these strike firings with the hope that we could better recreate the green or red spotting we saw in pictures. We made a shaker (similar to a pepper shaker) and just after we glazed our pots, but while they were still wet, sprinkled them with black copper oxide. Black copper is coarser than copper carbonate and we thought that it may not completely melt, thereby producing some green spots.

 

We reasoned that, since our grinding technology has greatly improved, the materials used today are much finer than those of the Qing dynasty, which may explain why you don’t see much green spotting in glazes. Just as we had hypothesized, the black copper oxide produced green and black spots with green or red halos around them.

 

Heavy Reduction Cycle (HRC) was fired to cone 022 (1100°F or 593°C), which is the beginning of dull red heat, and then put into heavy reduction (>0.80 on our oxyprobe). This was continued until cone 10 was bent to the 3 o’clock position and then the kiln was closed up and allowed to naturally cool. The results were nothing in the Peach Bloom range but rather the standard copper reds with very dark red to black to purple with some mottled surfaces.

 

R 08/11 Reduction Cycle started reduction at cone 08 and held to cone 11 (0.72 on the oxyprobe). This is a little later than the standard reduction cycle, where you start reducing copper reds at cone 010 and we also went a little hotter, to cone 11.

 

Wood Oxidation Firing was attempted because we had the offer of space in a firing and we thought we might learn something since the Chinese potters of the Qing dynasty fired with wood. Unfortunately, the firing was mainly oxidizing and so there were no Peach Blooms acquired in this firing.




Results

 

  • The crystallization of the aged glazes showed a great difference in the outcome of the tiles. See Jeff’s Red and Pete’s Cranberry.The aged Splotchy Lavender also produced some very interesting mottled results.
  • Layering a blue celadon glaze with a copper red over it, as well as sandwiching the red in between two blue celadon coats, gave some wonderful mottled blue reds (Pete’s Cranberry).
  • Higher amounts of tin oxide in the glaze (0.15%–2.5%) did make the glaze more milky and mottled (Easy Red).
  • Higher amounts of magnesium carbonate appeared to produce more pinks (Norton Red).
  • Using black copper oxide as the source of copper and/or sprinkling it on while glazing produced green and red patches (Tom Turner Flambe 2 and Splotchy Lavender).
  • Additions of copper carbonate (1%–3%) in the base recipe pushed it toward green and yet still retained some red highlights (Easy Red and Norton Red).
  • Refiring the over-reduced peach blooms (S2) in electric bisque with other greenware pieces of dark stoneware or earthenware gave the glazes a wonderful satin surface while re-oxidizing the red to blue with spots. This satin surface was caused by the gases (sulfur) being released from the earthenware clay. This will often happen if you mix dark greenware pieces in a majolica glaze firing (Tom Turner Flambe 2 and Splotchy Lavender).

 


 

For Further Testing

 

Although we did achieve our goal of reproducing some beautiful Peach Bloom glazes, there is still a lot more to be learned about this elusive and beautiful glaze. Our testing led us to new and unusual methods of glazing and firing and opened many new roads for further testing. Layering two different copper reds and strike firing gave some more varied surfaces. Lower flux amounts made flat pink, as did under firing copper reds to cone 9 rather than cone 10. We did not get definitive results from saggar firing with Oribe or copper wash on the inside of the saggar. We also got no definitive results from spraying tin and copper over a celadon or under firing celadons, but that is not to say we have eliminated them from testing.

 

Through it all, it turns out that Lindsey was right: Occasionally, if everything comes together just right, magic can happen!

 

 


 

the author John Britt is the author of The Complete Guide to High-Fire Glazes. For more information about John and his work, see www.johnbrittpottery.com.

research assistant Lindsey Elsey holds a BFA from Appalachian State University in Boone, North Carolina.

 


 

Tom Turner Flambé 2 – cone 10 reduction
Vase, 11 in. (28 cm) in height, wheel-thrown porcelain, with Tom Turner Flambé 2 Glaze, black copper oxide sprinkled on when wet, bisque fired to cone 06, gas oxidation fired cone 10, striking for 2 hours at 1500°F, refired in electric bisque to cone 06 along with greenware pots made of dark stoneware.
Barium Carbonate 3.89 %
Dolomite 5.56
Gerstley Borate 11.12
Whiting 8.34
Wood Ash (soft wood) 1.00
Zinc Oxide 1.67
Kona F-4 Feldspar 41.72
EPK Kaolin 1.67
Silica 25.03
100.0 %
Add: Tin Oxide 0.83 %
Copper Carbonate 0.42 %

 

 

Daly Red with Titanium – cone 10 reduction
S1 S2 HRC R 08/11 Wood Ox.
Firing Cycle tests
Bone Ash 1.0 %
Talc 3.0
Whiting 15.0
Zinc Oxide 2.0
Ferro Frit 3110 17.0
Nepheline Syenite 35.0
Silica 27.0
100.0 %
Add: Tin Oxide 1.5 %
Titanium Dioxide 3.0 %
Copper Carbonate 1.5 %
Bowl, 6 in. (15 cm) in diameter, wheel-thrown porcelain, with Daly Red Glaze (w/titanium dioxide), gas-oxidation fired cone 10, very quick cooling to 1500°F, then striking for 2 hours.

 

 

Splotchy Lavendar – cone 10 reduction

 

S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Barium Carbonate 2.0 %
Lithium Carbonate 2.0
Whiting 15.0
Zinc Oxide 4.0
Hommel Frit 14 7.0
Custer Feldspar 50.0
Silica 20.0
100.0 %
Add: Tin Oxide 1.0 %
Copper Carbonate 0.6 %
Bentonite 1.0 %
Teabowl, 5 in. (13 cm) in height, wheel-thrown porcelain, with Splotchy Lavender Glaze, black copper oxide sprinkled on when wet, gas-oxidation fired to cone 10, striking for 2 hours at 1500°F, refired in electric bisque to cone 06 along with greenware pots made of dark stoneware.

 

 

Pete’s Cranberry – cone 10 reduction
Pete’s Cranberry New Mix
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests

 

Pete’s Cranberry Aged Mix
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Gerstley Borate 10.20 %
Whiting 11.10
Custer Feldspar 73.80
Silica 4.90
100.0 %
Add: Copper Carbonate 0.35 %
Tin Oxide 1.00 %
Teabowl, 5 in. (13 cm) in height, wheel-thrown porcelain, with Pete’s Cranberry Red Glaze sandwiched between Sam’s Satin Celadon Glaze, gas-oxidation fired cone 10, striking for 2 hours at 1500°F.

 

 

Easy Red – cone 10 reduction
Easy Red
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Easy Red with Copper Carbonate 0.15%–2.50%
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Easy Red with Tin Oxide 0.5%–1.0%
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Gerstley Borate 10.7 %
Whiting 10.7
NC-4 Feldspar 40.3
Nepheline Syenite 14.8
Spodumene 6.7
Silica 16.8
100.0 %
Add: Tin Oxide 1.0 %
Copper Carbonate 0.3 %
Red Iron Oxide 0.1 %
Bowl, 8 in. (20 cm) in diameter, wheel-thrown porcelain, with Easy Red Glaze, gas-oxidation fired cone 10, striking for 2 hours at 1500°F.

 

 

Jeff’s Red – cone 10 reduction
Jeff’s Red New Mix
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Jeff’s Red Aged Mix
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Barium Carbonate 4.4 %
Dolomite 8.7
Whiting 8.4
Zinc Oxide 1.7
Ferro Frit 3134 8.7
Custer Feldspar 41.9
Silica 26.2
100.0 %
Add: Tin Oxide 2.6 %
Copper Carbonate 0.5 %
Bentonite 1.0 %

 

 

Norton Red – cone 10 reduction
Norton Red with Copper Carbonate 0.5%–4.0%
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle)
Norton Red with Magnesium Carbonate 0.5%–4.0%
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle)
Whiting 14.1 %
Nepheline Syenite 44.4
Ferro Frit 3134 13.1
Kaolin 3.0
Silica 25.3
100.0 %
Add: Copper Carbonate 0.2 %
Tin Oxide 1.0 %

 

 

John’s Red – cone 10 reduction
S1 S2 HRC R 08/11 Wood Ox.
(Firing Cycle) tests
Talc 3.64
Whiting 13.64
Zinc Oxide 4.55
Ferro Frit 3134 9.09
Custer Feldspar 48.18
EPK Kaolin 5.45
Silica 15.45
100.00 %
Add: Copper Carbonate 0.80 %
Tin Oxide 1.20 %
Cup, 5 in. (13 cm) in height, wheel-thrown porcelain, with John’s Red Glaze outside, Pinnell Celadon inside, gas-oxidation fired cone 10, striking for 2 hours at 1500°F.

 

 


Article printed from Ceramic Arts Daily: http://ceramicartsdaily.org

URL to article: http://ceramicartsdaily.org/ceramic-supplies/ceramic-glaze/experiments-in-peach-bloom-extensive-testing-reveals-secrets-of-an-elusive-ceramic-glaze/

Copyright © 2008-2012 Ceramic Arts Daily. All rights reserved.