An Approach to Single Firing-Further In

8/3/2019 An Approach to Single Firing-Further In

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Further in, 0my love, take me further in,So deep in this mystery, my tears on yours depend,

And they like some wild river flow as we go further in,Further in

-Greg Brown

" Th re e A m big uo us B ow ls ," to 8 in . ( 20 em ) i n h eig hl, Ih ro wn a nd a lte re d s to ne wa re , r ib be d- slip s ur la ce , w ith m u tlip le s pra ye d g la ze s, s in gle fire d 10 Cone 10 r educ ti on .H ill m ak es h is p ie ce s s o Ih ey a pp ea r a s a lIu id w ho le -th e u nd ula tin g rim , th e rib be d s lip a nd th e c ut fe et 01 th e b ow ls w o rk in c on ju nc tio n w ith e ac h o th er .

A s I ponder the twenty years that have passed since I initially wroteabout single firing [see "An Approach to Single Firing," January1986 Clvl], I think about how much has changed and how muchhas stayed the same. Since r am currently recovering from bypasssurgery, one very big thing has changed for me! I faced my ownmortality and came om swinging. Hopefully I will be here in an-other twenty years to give one final update on single firing!

In spite of historical precedents, the field of contemporary ceramicshas never embraced single firing. In the beginning, I was naive enoughto imagine that studio potters would see me advantages and begin toexplore raw glazing. Although I know my article and workshops haveinspired many, it has mostly been a solitary road I have traveled. Imay not have changed me way the pottery world viewed single firing,but single firing has perpetually guided and focused my efforts. Throughmy experiences, I learned to trust the process, to listen to me lessonsmy materials taught me and [0always follow my heart.

Everyone knows mat single firing eliminates the bisque, savingboth fuel and labor. In reality, however, one must extend the firingduring burnout (1400-1700F), which minimizes fuel savings.The labor saved by not having to stack and unstack bisque firingsis indisputable, bur this alone would never have been enough. Forme, the principle advantage of single firing is the connection I feelto the process.

When I first experienced single firing at a salt glazing workshoptaught by Peter Sohngen, I was in undergraduate school and had notyet found my voice in clay. There was often a lag time of weekswaiting for bisqueware and glazing felt like an afterthought, as myheart was always with the new pots spinning off my wheel. Glazinggreenware quickly connected the separate stages of pottery making forme; the throwing, decorating and assembly Rowed naturally into theglazing and firing cycle.The entire process became cohesive. I swore Iwould never fireanother bisque kiln and have not wavered for 33 years!

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Single firing has not been without its frustrations, however. Mypots have cracked and delaminated in the glazing process. They haveblown up and blistered in the firing. I have never felt significantlimitations, but raw glazing has always guided me, influencing me tospray glazes, to make robust forms wich well-defined rims, and to bemore decisive, both when throwing and glazing.

(layUntil the mid 1990s, I formulated and mixed my own clay bodies,following the guidelines I prescribed in my 1986 article, focusing ontight bodies with a high percentage of ball clay. I had considerable~uccess, bur was never able to totally avoid [he frustrations incurredduring glazing.

Since 1995 I have been using Laguna B-Mix exclusively. It is anextremely plast ic, l ight gray (in reduction), porcelaneous body withbentonite. It resists rehydration during glazingmore effectively than any clay body I have used.In fact I would say if its working properties, colorand temperature range appeal to you, that there isalmost no other choice. That said, all clay bodiesinvolve compromise and none have universal ap-peal. For instance, B-Mix's extreme plasticity re-quires conscientious joinery to avoid drying cracks.

I have always been a precise thrower, avoidingthin spots that can lead to delamination. I dis-cussed this problem in my 1986 article, but hadnot yet named it. Delamination can occur as thewater penetrates the wall from borh sides afterglazing and rehydrates the day, causing it to ex-pand. If the wall is too thin, the day can rip apart,leaving a void in the center of the wall with acorresponding bump and sometimes a crack onthe surface. Alchough this looks somewhat likebloating, it occurs during glazing, rather thanfiring. B-Mix nearly eliminated delamination forme, leading to a greater freedom in my throwingand assembly of pots than I had ever felt before!

Since most potters use commercial day, theonly advice I can give is try your current bodyand se e how it works. The unique properties ofyour day body will have a tremendous impact onyour success and on whether you perceive singlefiring as a joyful experience or as a needless hassle.There are literally hundreds of commercial claybodies available, and a great many of them can besuccessfully raw glazed and single fired.

GlazeWhen raw glazing, one must make the decisionwhether to glaze bone dry or leather bard. I don'trecommend glazing between these stages, as thepot is likely to be dry at the rim and wet near thefoot. This will lead to a discrepancy in waterabsorption and potential cracking. I have always

glazed my pots bone dry at the end of a work cycle, but if you glazeleather hard you must glaze when the pot is ready. The pores ofleather hard pots are still partially filled with water, so there shouldbe lower water absorption and less chance of delamination or crack-ing. On the other hand, leather hard pots will continue to shrinl~,requiring a higher percentage of clay in the glaze and thus limitingglaze choice.

'W'hen a raw pot is glazed, the clay renydrates and subsequentlyswells. Then as the water evaporates i t contracts. Ifhe glaze recipehas no clay it will lack plasticity and. flake off as the pot dries. If theglaze contains some clay, but not enough, it is likely to crawl duringthe firing. In 1986, I recommended a lower limit of 5-10% kaolinand 2% bentonite, but I have recently used as little as 3-5% kaolinand 2% bentonite. I even use one glaze, Cornell Iron Saturate,which has JUSt3% bentonite for i ts total clay content.

"Watering Can," 9V , in. (24 em) in he ight, thrown and a l te red s toneware,with trailed s li p, m u lt ip le s pr ay ed g la ze s, S in g le f ir ed t o Go ne 1f l i n renuc tten .

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There ate a number of other glaze ingredients that, either throughflocculation, defloccula tien or excessively small part icle size, keepglazes wet excessively long after application. Gerstley borate is a realculprit and, to a lesser extent , most boron fri ts. Other ingredients tobe wary of are soda ash, tin oxide, zinc oxide and possibly titaniumdioxide. Any of these can be used successfully, but with an increasedchance of delamination. My personal solution has been to sprayglazes, as water absorption is minimized. Creative thinking willsolve just about any problem in ceramics,

Glaze ApplicationJust about any glazing technique used for bisqueware can be adaptedfor single firing. Pouring, dipping and brushing are all viable if youconsider water absorption and the potential it has to weaken thewall. However, when pour-ing and dipping, there is alimit to how many coats canbe applied, and both the in-side and the outside should

piece, the more likely this is to be a problem. If a pot blows up in aglaze firing, there will be shards scattered throughout the kiln land-ing on horizontal surface such as rims, lids, plates and bowls. I'velost nearly half a kiln load from one explosion! It's nor difficult tosafely preheat the kiln, but i t does require patience.

In fuel burning kilns, the t0p third of the kiln can be severalhundred degrees hotter than the bottom during the early stages ofpreheating. In a downdraft kiln the bottom will quickly catch up asthe chimney begins to draw. Therefore, I recommend a slow preheatto 500F. I take seven hours, but if you are firing large, thicksculpture you might need to go slower.

Once beyond preheating, the temperature can proceed quicklyto the burnour phase. Between 1400-1700op, the kiln should beoxidizing with enough time allowed for the organic material to

thoroughly burn out. Typi-cally, pots go through thistemperature range threetimes: once asthe bisque kilnis fired; again as it cools; anda third time during the glazefiring. When single firingyou have only one chance toburn out the volatiles! If the

be glazed in close succession,so they expand and contractsirnultancouslv, Handlingpots can be an issue-cer-tainly glaze tongs are out, butpicking up a pot by the rimorsqueezing the foot also canlead to cracking.

For the last ten yearsspraying has been my pri-mary glazing technique (see"Spraying Glazes," Spring200 2, Po tt ery Ma ki ng Il lu s-trated); I pour the interiorof all enclosed forms, but use the spray gun to glaze the exterior ofpots, and for both the inside and. outside surfaces of open forms,The undeniable advantage of spraying is that water evaporates as theglaze travels from the tip of the spray gun to the day surface.Multiple layers can be applied without the risk of excess waterabsorption, making it unnecessary to glaze the outside of the potimmediately after the interior.

In the '70s 1sprayed glazes to emulate atmospheric firing ..I soonrealized the practical advantages and spraying became a primarymethod. As I became more skilled I developed techniques thatallowed me to both isolate color on my rims. and feet and subtlyblend glazes throughout the body. Now thirty years later, it is dearhow my technical skill and aesthetic sensibility developed side byside, each influencing the other.

atmosphere is not oxidizingor if you go through thisstage too fast you risk trap-ping organic material underthe melting glaze. After theglaze melts, the organic va-pors will begin to escape,causing the glaze co blister,pinhole and, in extremecases, the day will bloat.

I fire a Geil gas kiln with a programmable computer. This hasbeen a blessing, as it prevents my impatience from getting in the wayof the ideal firing. IfI didn't have a computerized kiln I would likelybe less careful with preheating and burnout. There is simply nosubsti tute for experimentation with firing schedules to see how theyinteract with specific clays and glazes.

Bowl, 10% in. (27 em ) in length. thrown and altered stoneware,with ribbed slip, mul tiple sprayed glazes, s ingle f ired to Cone 10 in reduct ion.

PiringThe worst possible disaster when single firing is to blow up pots. Allraw POtS have water in them (both atmospheric and chemicallycombined) and unless they were glazed weeks ago, absorbed water. Ifthe temperature rises too quickly as water is turning to steam, anexplosion can occur. The tighter the day body and the thicker the

Steven Hil l's Single Firing Schedule(Pre-Reduction)

Room temperature to 225F (107C): three-hour ramp,with arwo-hour soak at 225F.

225-500oP (l01-260C): two-hour ramp with no soak. 500-1 500F (260-815C): three-hour ramp, with a two-hour soak at 1500F.

150Q-1700oP (815-926C): two-hour ramp, with a two-hour soak at 1700F.

1700-1800F (926-982C): approximately one hour inheavy reduction.

1800oP-Cone 9: approximately six hours in light reduction, Cone 9-Cone 10: approximately one hour in oxidation.Once the kiln is in reduction it is fired manualLy.

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Two mugs, each 5 in . . (13 em) in he ight, thrown and al tered stoneware, t rai led slip, wi th mult ip le sprayed qlazes,single fired 10 Cone 10 in reduction, by Sleven Hill, Kansas C'ity, Missouri.

Oxidation and soaking are still important if you are single firingin an electric kiln. If you don't vent the kiln by actually drawingfresh air through the kiln chamber, there can be local reductioncaused by the carbonaceous material in the clay. This reduction canprevent thorough burnout and cause blistering. Don't just assumeyou are in oxidation, even if you are firing electrically!

Further InIt is easy to look back on the last 33 years and see the profoundeffect that single firing has had on my work and on my career.Although I never saw it as a limitation, the growth of my work hasbeen subtly directed by the constraints of raw glazing. It led toexpanded use of the spray gun, which allowed me to both isolateand blend glazes in ways that eventually became a signature. In1995, after traveling toTuscany, I wanted my pots to have surfaceswith the rich earthy colors and the soulful depth I saw in themultiple layers of peeling paint visible on ancient stucco walls. Forthe first time, I also saw the architectural attributes containedwithin my organic forms. Spraying was a natural way to achievethese subtle variations of color and texture, but it also allowed meto isolate glaze on my rims, feet and handles, in order to emphasizearchitectural features.

Another undeniable effect came when "An Approach to SingleFiring" was published twenty years ago and the ceramics worldbegan to notice my pottery. That exposure led to my first fewworkshops, which eventually developed into the very core of mycareer. Idiscovered a passion for teaching and I'm Iortunate co havehad innumerable opportunit ies over the last twenty years.

Obviously, single firing is 110t for everyone and no one shouldpursue a way of working that feels uncomfortable. Also, if the goal isextreme delicacy and thinness, deep carving, or complex painterlysurface design, there are important reasons to bisque fire. The issue is to.follow your passion, whatever it might be, with everything you've got!

With my first single firing experience, Iwas affected on a primallevel and inspired to go further in. A s Iachieved the necessary skillto focus beyond technique, my artistic vision developed and singlefiring began to soulfully connect me to my work. Isimply openedmy eyes _and heart, and let influences flow through me. Music,nature, architecture and pottery all left their mark. Single firinghelped unify varied sources of inspiration, while determination hasgiven structure to my journey for 33 rich and rewarding years.

the author Steven Hilt o wn s a nd o pe ra te s R ed S ta r S tu dio s in K an sa sC i ty , M i s sour i. See t ouno . reds tar s tud ios . org .

Ceramics Monthly January 200654 (

An Approach to Single Firing-Further In

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