New Zealand Potter V0123/2 SPRING 1981 Contents Wood Firing with a Bourry Box kiln 2 Peter Gibbs’ Bourry firebox 2 Glen Beattie’s Bourry firebox 5 Primitive pit firing 6 Some Coromandel potters 7 Paul Tobin 7 Dear potters, Warwick Lidgard—Shino 10 Ceramics 81 was a Articles should be specific, Andrew and Jeannie Van der Putten 12 milestone for the development with supporting diagrams or Barry Brickell 14 of pottery in New Zealand, illustration where necessary Urban Co-operative 16 providing us with a reference giving the kinds of details Firing updraught fibre & gas kilns 17 which we can go readers want to know. point from Outreach 18 forward. (Payment is made for Fletcher Brownbuilt Pottery Award 20 While a great deal of informative technical articles.) 21 potting will follow tried and Space allotted 'is usually Moyra and Gary Elliot—copper reds true techniques there are many determined by the quality of the John Parker—domestic wares 24 of you developing new thoughts contribution and the type of Gerald Hope—adapting to LPG 26 and materials and methods, information offered. When Wendy Ronald—hand pinched pots 28 extending existing techniques, judging an article’s worth we Copper reduction in raku firings 29 fOr example producing glaze ask: is it interesting: is it Summer workshops 30 ' effects, oil spots, crystals, helpful: are the ideas expressed Potting in Waikato 31 lustres, Shino and working on clearly: and above all, is it Elizabeth Woodfield’s ball mill 37 kiln and firingadvances. original and creative: You may New Zealand Potter is a non-profit making magazine published twice annually. Circulation is 6,500. 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Waiatarua close to Auckland.- He has contributed to this issue under what might be fl PO. Box 12—162 Wellington North, New Zealand headed Twists of History “a quasi historical note”. (See centre pages.) mk printed by Deslandes Ltd, Wellington — ISSN 0028-8608 Photograph: Steve Rumsey. I ”4*. New Zealand Potter Page 2 New Zealand Potter Page 3 Wood firing with a Bourry Box kiln It was in 1911 when Emile Bourry in his Treatise on Ceramic Industries described his firebox for woodfired kilns that minimised the amount of ash free to circulate around the ware. Bourry wrote: ood can be burnt in the midst of the ”77% Wgoods when the latter are not injured a: // by contact with ashes which are easily carried about by the draught. This method of heating presents no other difficulty than that resulting from putting of wood into the kiln, an operation which must be > frequently D repeated, >- D though it causes the entrance of cold air and a serious loss of heat. These defects are specially noticeable when faggots are used, and to remedy them openings for charging r~_..._._ should be lengthened outwardly to the shape H rt LJ Duo .1“:_.___ ’530 of tunnels, closed by a sheet-iron plate [1: suspended at the upper part. These charging tunnels hold so much wood that any air drawn D in by the draught is warmed while the charg- __—_—. ing is taking place. This arrangement, which is L——--_ used especially for faggot fuel, is also ap- L.___D6-__ plicable to intermittent kilns as well as to con- tinuous kilns. Wood in the form of logs may be introduced into the latter kilns exactly as if it FIG. 132,—Furnace for wood. were coal. the goods to be burned. The air enters by a ing through the ashpit door. This type of lower passage which forms an ashpit and fireplace is built into the kilns; it gives very PETER GIBBS leads into the upper passage through the long flames and is suitable for all kinds of BOURRY BOX TYPE K|LN openings arranged regularly in the dome of it, work. For slow firing, the logs must be re- but not opposite those of the first one. A part placed by faggots, or the upper opening may NOTES: of the fuel falls into this ashpit and is con- be closed with a damper. Primary Air 75 x 112 sumed there while heating the air. This ar- Secondary Air 75 x 112 rangement is specially applicable to up- draught kilns and can easily be modified when Mouse Hole 75 x 56 necessary. 300 Lower Stoke Hole 225 x 225 For the production of high temperatures, L Hobs various patterns of fireboxes are used. The Bag Walls Fm. Lit—Furnace tor burning wood. type represented in Fig. 132 gives good results Flues to Chimney provided all the logs used are of the same 625 Throat Arch I560 TIQTWPQW?’ length. These are piled in the upper opening of 570 Chimney — Height 5280 Blocks of wood may also be burnt in the fireplace and rest on two brickwork projec- Final Top Dimension 275 x 550 fireplaces with gratings as in Fig. 131. The tions. The combustion takes place by the air f/‘/./ hearth should be prolonged beyond the front passing between the logs, the flames follow— zoo of the kiln, and the wood charged through an ing the direction shown by the arrows. The / é upper passage, the dome of which is placed embers which fall to the bottom of the fire- ? immediately underneath the kiln and carries place help the burning, owing to the air enter- stooping. The total inside volume is Two potters offer their experience 50 angle iron holding the fireboxes. Briefly the firing goes as follows— 2.5m3 (88 cu.ft.) and the available woodfiring with a Bourry firebox This was bolted together with 50 mm from cold: rods. The arch was buttressed with stacking space is just over 1.5m3 (55 ‘\\/ 3—4 hours: Fire in lower stoke hole cu.ft.). railway iron backed by 50 x 50 angle doorway one side only for first iron. The firebox lids were made of 5 I generally stack bigger pots bottom hour or two. Peter Gibbs—Nelson mm steel backed up with low grade and top, and fairly tight in the middle. 2—3 hours: Fire on floor of firebox. fibre. In theory this was a good idea, 2—3 hours: Top loading scraps or but in I built my kiln in Spring 1979. My practice, most of the fibre was Before firing I try to be fairly careful longer pieces until 800 ° to 900 °C. reasons for choosing this type of knocked off after a few firings. I made to warm up slowly, if possible having a 8—12 hours: Stoking on hobs. With firebox were, firstly, I wanted to be the lids in two halves with an overlap- warm-up fire for a few hours the previ- the exception of the first hour or ping ous evening. This is in one firebox able to easily fire the kiln alone and flange, and fixed a pulley in the two, I keep the fireboxes full. This secondly, I could handle two fireboxes, steel work above, so that one lid could only, right back in the lower stoke hole necessitates stoking every 10—15 giving a more even firing. I used two be held open during stoking. The sec— door. The general firing pattern I fol- minutes. During this time the low is fairly well books when planning: ”Layed Back ondary air holes are about twice as big documented in both primary air is full open, the secon- Wood Firing” by Janine King and as necessary, but can be used as secon— the books previously mentioned, al- dary air half or less, and the lower though I follow a simplified Stephen Harrison and ”Pioneer Pot- dary stoke holes towards the end of the procedure stoke door and mouse hole are large at around 600 °~7OO tery” by Michael Cardew. The first firing. On odd occasions when a °C.