Pottery In Australia Vol 35 No 1 Autumn 1996

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~ring Iden rood ::r to my ,nse, : the here 1e I and the rom din was in the and Vin the ork ,uth )tly life nd lar are s I her Its er cal he nt w he · er th, ed . t. of it. a. is f n a f THE ESSENTIAL ASPECTS FOR THE PRODUCTION OF A GOOD TERRASIGILLATA The Selection of Clay for a Good Terrasigillata The best clay for the production of terrasigillata is an illitic clay. The illites have a variable crystal structure which gives rise to crystals that are extremely small, poorly defined flakes, often six sided. They have an average amount of 6% of potassium in the crystal lattice. The presence of this potassium and other fluxes such as iron and magnesium cause early vitrification. According to Grimm the vitrification may start as early as 900 degrees centigrade. This is due to the intimate distribution of fluxes throughout the material. Because the crystals are small, the green strength and drying shrinkage are high. The drying rate is slow and the clay very plastic. Because of the sheet lattice structure the clay minerals have their surfaces in contact. The smaller particles giving a greater surface contact area. Thus aiding strength, plasticity and adhesion. The Production of a Satisfactory Colloid Colloidal particles are those of a finely divided substance which is dispersed throughout another substance. The finely divided particles are called the dispersed phase and the substance through which they are dispersed is the dispersion medium. Both phases are called a colloid. All particles of a substance tend to have the same electrical charge resident on the surface thus they repel one another if dispersed in a liquid. The Use of a Detlocculent I add calgon which is a sodium hexametaphosphate to the dispersion medium. The amount used in 1 % - 3% to the weight of dry clay used. This creates the situation where the particles all have the same electrostatic charge, repel one another and are unable to aggregate. The Dispersion Medium Distilled water is used as a dispersion medium rather than tap water. This is to ensure that no minerals or salts which may be found in the tap water are included in the deflocculated slip. Methodology A suitable clay is selected, dried and crushed to a powdery state. Distilled water is measured out in the ration of 2:1 water : clay for coarse clay, or 4 : 1 for fine grained clay. The deflocculent is added to the water - the amount varies from 1 % to 3%. The clay is added to the water and allowed to slake down for 30 minutes. The clay is then passed through a sieve, stirred and left to settle in a clear container for a few days. The thin colourless water at the top is then siphoned off and discarded. The dark sediment at the bottom is discarded and only the middle 2/3 of the watery slip is maintained. This slip should have a specific gravity of 1.2 or less, and it needs to be thickened before it is used. This can be done by allowing the water to evaporate off naturally; or simmering the slip on the stove, very slowly until it reaches the consistency of thin cream and has a slightly marbled appearance. Application The terrasigillata can be applied in a number of ways. It can be brushed or sprayed on to green or bisque ware; it can be applied to already fired ware and can, in fact, be fired numerous times . It should not be applied too thickly or it may peel off. Spraying has a better finish than brushing, as the brush marks may be visible. Firing Techniques There are an enormous range of temperatures through which terrasigillata can be successfully fired. Some authorities suggest 900°C - lCXX)'C others suggest 1050°C - 1150'C degrees. I personally have found that two firings are advantageous. The first firing is taken to cone 03. The pot is then re-sprayed and the firing taken to cone 04. This gives me a good sheen, particularly over the black areas. The pots must be fired in an oxidised atmosphere to obtain bright colours. Black Terrasigillata In order to obtain the black colouring of some of the pots, I use a base of Walkers throwing clay, made up into a terrasigillata. To 80% of the Walkers clay I add 2% of each of the following: Black Iron Oxide Red iron oxide Copper carbonate Cobalt Manganese oxide Coloured Terrasigillata In order to obtain coloured terrasigillata a white terrasigillata was made up using the following materials" Cresta BB Frit 3110 Distilled water Calgon Underglaze colours can be added. 20 .5 80 ISSUE 35/1 AUTUMN 1996 + POTTERY IN AUSTRALIA 47
I Albie Herbert The artist has a role to play highlighting the complex conflicting motives that pull and tug at the big environmental picture. Below: "Striding Men", from Endangered Species series. Ceramic, wood. Opposite: "Odyssey". Ceramic. n Rwanda the competition between human needs and nature threatens the mountain gorilla's sanctuary. Already prey to poachers, now millions of refugees fleeing war and poverty in neighbouring countries plunder the dwindling forest resources for firewood, which is essential for their survival. Who has the greater need? Of course these people have a right to live but the gorillas' plight must be recognised. In Western Australia old growth forests are disappearing at an alarming rate, but jobs and industry are at stake if we stop. The numbat, chudich, bilby and many other delightful creatures and plants are at risk if we continue with our present development. The dilemma is so profound; awareness is not enough. People with passion are needed to sway the argument and who better than artists? They have no vested interests and a powerful communication tool in their creative medium. To emphasise these issues a narrative approach has bee a 1, rad Ind ing car end one 1 iSSl mai rati nur allo a VI into [ con are mar trul dra dur out con hel1 the~ crec F a cc aPI= rese off enh risk rely the pre (hif surf: diet stair and F be 1 are, to exp Albi~ 139 1 Hilla 48 POTTERY IN AUSTRALIA+ ISSUE 35/1 AUTUMN 1996
Page 1 and 2: POTTERYin AUSTRA~ Vol 5 Number 1
Page 3 and 4: • I C s b ll '\ V s [ ll C fr C l
Page 6 and 7: Showcase a Recent exhibition work F
Page 8 and 9: ul ) s. t . e o S e n t s t I e a o
Page 10 and 11: SHOWCASE Above: Cheryl Sobott-Tom.
Page 12 and 13: ISSUE 35/1 AUTUMN 1996 + POTTERY IN
Page 14 and 15: tic to re ar to at ts a. e o , d t
Page 16 and 17: Tea pot. Salt glaze. 15h (cm). d .r
Page 18 and 19: Wood Fired Shino Dish. d45cm lS n l
Page 20 and 21: s y s r Out of the Ordinary JENNY O
Page 22 and 23: the ard ted ure ng be ve or s I the
Page 24 and 25: ! large as ld ln en CD CD 0 I ~ >
Page 26 and 27: of fal of ts, lly of ed sm ith t a
Page 28 and 29: the the ats e. ite , a her just on
Page 30 and 31: the ;till of Jrk ~ns he by as nd ey
Page 32 and 33: a ie to d e it g s e y e r r a l r
Page 34 and 35: St e th to e se a in d e ft Austral
Page 36 and 37: s e. ly ct to e e e e ?''. ff as ly
Page 38 and 39: H ave you heard the old adage 'two
Page 40 and 41: he to >US tly 1e, Ne of to as in ls
Page 42 and 43: the r to ous and to and ing s to nd
Page 44 and 45: md : to )Ur 1 a 1ed as 1ce an h's l
Page 46 and 47: "Crescent Vessel", 1995. Stoneware/
Page 48 and 49: e 3tS, l Above: Lynley Northcott, c
Page 50 and 51: Musical Abstractions Vivian Cohen h
Page 54 and 55: e er ue so n n ul as been adopted f
Page 56 and 57: d ion a act the As to ep ing for ic
Page 58 and 59: Right: "Figure Dancer I" Fleur McAr
Page 60 and 61: Glebe Pottery Studio Setting up a s
Page 62 and 63: to d? to he ) it ns g ey er s is is
Page 64 and 65: 1les ed On vas he be aS he a he he
Page 66 and 67: on t of ire eg uel he lOt at ly at
Page 68 and 69: 1le lly :ct he nd . a ce to :d. ut
Page 70 and 71: ly re er ip d y 6 in es d s, 8 d h
Page 72 and 73: T tO just ln is and ;ize, ious sed
Page 74 and 75: NO. OF CONTROL CuSTOM SPARE WARRANl
Page 76 and 77: md 1ite e it to lgh gh of a ty, of
Page 78 and 79: y e at t t , it Left: Nguyen Thi Do
Page 80 and 81: op a e ck de It n !, d a e is a of
Page 82 and 83: A ROUNDUP OF LOCAL NEWS AND EVENTS
Page 84 and 85: are mds Has rom f us )rd. l to size
Page 86 and 87: sts am ing •• POTTERY IN AUSTRA
Page 89 and 90: Subscription Order Issue 35/1 Autum
Page 91 and 92: Traditional and Contemporary Pa ·
Page 93 and 94: Could these be the best electric ki
Page 95 and 96: INTERNATIONAL WORKSHOPS 8th Nationa
Page 97 and 98: CAST IRON BANDING WHEELS E13/A E13/
Page 99 and 100: CLAYWORKS FINE FILTERPRESSED STONEW
Page 101 and 102: ( (/ Sydney College of the Arts } T
Page 103 and 104:
VIDEO Wo1lKSHOPS POll PoTTEllS Form
Page 105 and 106:
VENCO DE AIRING PUG MILLS all stain
Page 107 and 108:
HTH MAUH - l~TH ArRlt t9r~~ IU~f{J
Page 109 and 110:
ARTS &. CRAFT.I" MARKET, ~OLD COAST
Page 111:
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Pottery In Australia Vol 35 No 1 Autumn 1996

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