What type of clays did you use?
How did you fire biscuit pots in a mains gas kiln?
What ingredients were your glaze recipes made up of, and how was your glaze decoration applied ?What were your glost firing packing techniques?
How did you control a glost firing in a 'reducing atmosphere'?
What type of clays did you use?
Throughout my career and up to 1988 I have always used clays purchased from - Potclays Ltd, Stoke on Trent, UK. The following clays provided for a wide range of forms and techniques :-Potclays....1118 Special Stoneware.
Potclays....1106 White ST Thomas.
Potclays....1104 Reduction ST Thomas.
Potclays....1114 Craft Crank Mixture.
Potclays....Silica N0 1 sand.
What mixes of clay and recycling methods did you use?
Apart from using the above clays individually, they were often mixed together by hand in the traditional manner, then pugged, and either cool stored or used immediately. Typical recipes included:-Potclays 1118 &1104.. 50/50 mix..a general purpose body, good throwing, modelling and light hand building.
Potclays 1118 & up to10% Silica No1 sand.. to give added body for throwing.
Potclays 1106 & 1114..50/50 mix.. very stable for larger hand building.
From 1998 onwards a totally different type of clay was introduced called :-
Morgan 'T' material, and when mixed with porcelain......... T & porcelain 90/10 mix............ and........ T & porcelain 80/20 mix..........Here in just two clays provided all the versatility and function required, together with a lighter background clay colour that was more compatible with my latest glazes. Included below are two clay recipes, for the porcelain, and the 1992 white grogged stoneware:- 1. PORCELAIN....................% ChinaClay........................56 FeldsparPottash...............23 Quartz.............................15 Bentonite..........................6 2. GROGGED STONEWARE..............% Hymod smd......................................61 China Clay......................................13 Industrial Crank.1153.......................13 Molochite..(-22,60's)........................13Mix ingredients together in tin bath dry and gradually add *water to suit. Fashion the mix into large balls of clay, leave the clay semi covered to lose enough of the excess water. Then pug the clay twice and cool store for three months.
* I used to save all the wheel throwing slops and water and stored it all in a large tub. This was sieved and added along with rainwater to each mix and which accelerated the maturing clay process. Recycling Clays :- The workshop had a collection of plastic rectangular basins which were used to collect all the used clay ready for recycling. To which where necessary the old water was added to rejuvenate the clay. Any excess was drained off and the basins were stacked up waiting for the next clay pugging day, where they would be gradually added to the new clay and put back into cool storage for a month or two. This method of mixing the old with the new, along with the old water, always ensured that each batch when it came out of the cool store was in the best possible condition to work with.
What were your favourite hand tools for making pots?
Most of my thrown pots were made on a 'Leach style' traditional kick wheel, and the hand tools for turning each form were made by hand in the following manner, and were light, very responsive to the touch and easy to use :-For the handles use 1/2 inch (10mm) copper tubing (bottled gas type pipe) of 5-6 inches (13-15cm) in length. Then visit your local friendly 'piano tuner' and ask for some of the stronger single piano wire. Method - Cut into suitable lengths to provide you with a cutting shape of your choice and sufficient to pass back up into the copper tube. The wire can be cut with a hacksaw and bent using two pliers and/or a vice and pliers. Then insert the two ends inside the copper tube and squash/press the tube sufficiently to hold wire in place. If desired the leading edge of the wire can be filed for a sharper cut, or just left round. You can also choose to fit a shaped wire at both ends of the tube for convenience. As to the type and shape of ends one might make depends on their function, but my list included the following and all were very easy and quick to make and lasted years :- Short / long/ wide..... square ends, oval ends, rounded ends, elliptical ends, V shaped ends, and wide fan shaped ends. The old saying 'that there is a tool for every job' rings true with me and most of the ones often used were handmade out of beech wood. See your local 'furniture maker' for off cuts. A hacksaw, a sharp knife and glass paper is all you need to finish the job. Of the more common tools that can be bought, two stand out as being really useful - the metal kidney in all it's varieties and the step like steel turning tool with a spade shape at one end and a elongated V shape at the other end, both filed to a bevelled edge.
How did you ensure a good fitting lid when making boxes?The method of making boxes varied from starting as either, a thrown form, or hand built, in which a base and top, or just top only, would be added to make the box whole. Then when the clay box was firm, and with the aid of a very sharp * knife, an irregular cut was made all round to separate the lid. The two halves are tidied up and normally the lid is carefully placed back on top, ready to dry out. It is at this stage that problems can occur, for there is a tendency for the two halves to move, twist, bend and maybe lose that neat joint effect. Then one day the solution presented itself quite simply. All I had to do just before replacing the lid for the last time, was to place a few drops of PVA woodworking glue around the rim at key points. The lid was then carefully positioned, the glue dried almost instantly on the porous clay, and everything stayed in place as one. In the Biscuit firing the glue burnt away and the lid retained it's shape. * A broken hacksaw blade sharpened to a very long thin point and bevelled on both sides, on an electric two wheel grinder.
How did you fire biscuit pots in a mains gas kiln?
It is just a matter of control and understanding the needs of the clay pots in the process. The rules can be described as follows to avoid any mishaps :-
The pots must be dry, but of course there are times when this is not possible, for damp winters and tight schedules all play their part. But if you balance the packing by evenly distributing the ware inside, not only by placing them in such a way that the flames can move around evenly, but also by ensuring there are no over dense areas of clay pots in the stacking. Keep ware inside of the baffle walls, and not directly overhanging the burner ports. In damp conditions the initial stages can be controlled by using the poker flame only. The poker, normally used to ignite each burner in turn, passes through holes at the bottom front of the kiln behind the baffle wall, and rests at the bottom between two burner ports. A gentle flame gradually warms up the kiln. At this stage keep the kiln damper at the base of the chimney almost closed. This allows the build up of moisture within the chamber, and it is this steaming effect alongside the gradual increase in temp which prevents damage to the pots. Depending on how wet things are, either hold on around 120 degrees centigrade ( as read from the top of the chamber) until the bottom temperature catches up, then gradually increase the temp and begin to open the damper a touch to gradually let out the steam. In time most of it will have disappeared and at around 210 degrees centigrade the first of the four burners can be turned on low, then remove and turn off the poker. At around 320 degrees centigrade light the burner diagonally opposite the first one. Both burners are now turned up to a medium setting, and the heat is being evenly distributed throughout the chamber. Open the damper fully to release all gasses and moisture. After 4.5 hours from this slow start the top temp should be reading over 500 degrees centigrade, and the clay will be passing through that irreversible chemical change into biscuit pot. At around 580 degrees centigrade the last two burners are turned on at medium setting. Now the temperature, once past the critical stage, can rise fast. At around 660 degrees centigrade all four 'Amal atmospheric injector' burners are turned on full. Push the damper a touch to contain the heat and watch the temperature rise to a fast finish. Somewhere between 5 and 6.5 hours to reach 1000 degrees centigrade, depending on conditions, turn all burners off, job done.
What ingredients were your glaze recipes made up of, and how was your glaze decoration applied?This could be a book in itself, for I have enjoyed working with hundreds of basic glaze recipes over a twenty five year period. Out of those recipes has come a whole new range of colours which evolved, through careful experimentation, by mixing glazes with glazes in the form of an artists palette. These in turn could be varied by their reaction to the base glaze underneath, the thickness of application of each brushed glaze on top, and the overlapping effects of one colour over another. Only a very brief guideline can be offered here, and I must stress that in their raw state many of these ingredients are harmful, and they should be handled with great care. Appropriate clothing, face masks, and gloves should be used when handling these glaze recipes. Those glazes containing Barium Carbonate, Vanadium Pentoxide, and perhaps Manganese, should not be absorbed into the skin, by for example mixing the glaze by hand. Even when spraying these glazes protective face and eye masks must be worn, and finally keep all surfaces clean and dust free. Follow these simple rules and all will be well. Now back to the glaze ingredients and their application. This could be a little complicated to follow without seeing the process in action, so it might help if one pot is used as an example so please click on Landscape Series No 18 . Briefly this is how this pot was made:-
This oval vase was first thrown on the kick wheel as a cylinder with no base. Later the walls were pressed into an oval shape, where a base and features were added. It was the tidied up, pressed with my stamp, dried out and biscuit fired to just under 1000 degrees centigrade. The kiln is unpacked and the biscuit ware is stored ready for glazing and decorating and then returned to the kiln for the glost firing.
Glaze Recipes :- All the glazes are given numbers for reference, and have a generic history - for example glaze no 1, the base glaze, becomes 1A,1B,1C etc when different colours are added. Then when, as often happens, changes and developments occur, Roman numerals are added - for example glaze 1B.1,11,111,1V,V etc. In this way it is possible to keep detailed records of all developments. Added to this is my palette of glaze mixes which are quite simple to create in the process of working on each piece. As long as each glaze is thoroughly mixed up in suspension, a carefully measured spoon quantity is taken and mixed with another glaze of choice in varying proportions - for example 2B1 / 28 -1/3, in a mixed ratio of 1 part of 2B1 to 3 parts of 28. It took many years of experimenting to find the right combinations that both looked interesting and at the same time behaved themselves together in the glost firing.
In this case the basic glaze is called No 28 and is of the Nephaline Syenite type :-
Recipe No 28.....................................% Nephaline Syenite..............................36 Dolomite..........................................14 Whiting............................................7.5 China Clay......................................24.5 Quartz............................................18What is interesting about this glaze apart from it's natural qualities of having a light creamy/green colour and soft touch when handled, is that when introduced to copper in the glost firing, a process of 'volatilization' takes place with the copper carbonate in a 'reduced atmosphere', where when carefully controlled can leave some warm pink effects on the surface of No 28 glaze which enhances the overall decoration.
The palette notes to remind me of what each mix of colours will turn out like is listed below from light to dark tones in sequence. For those who have never experiencing the process of glazing before a brief description might be of use. In this case the vase was quickly dipped into a large bucket full of No 28 glaze and water. This initial coating of the powdered glaze is absorbed onto the surface of the porous biscuit pot. After wiping off the excess glaze of the base of the vase, it is ready to have the decoration applied. With a number of small tubs with the glaze mixtures in and their brushes I am ready to start painting. But unlike using tubes of paint where one can see the true colour immediately, here in ceramics it is quite different. For each glaze will often have a nondescript colour, a pale grey, buff, brown, black, nothing like what they will turn into when melted around 1280 degrees centigrade. So one has to forget what things on application look like, and try to picture the end result. This is why it is so important to be able to rely on each glaze ingredient and know exactly what it is going to do.
The Glaze Palette :- Basic Glace No 28..........colour light cream with a green tinge. Add more No 28 over No 28...... opaque cream colour. Glaze mix 2B1/28.. ratio 1/3.....brushed over.... splash of pink/red colour. Glaze No 1BV1... brushed lightly over ..... soft yellow ochre/brown colour. Glaze mix 1BV11/28...ratio 50/50...brushed over....light blue grey colour. Glaze mix 2B1/50X...ratio 1/3.... brushed over...rich red colour. Glaze 2B1...brushed lightly over.... greens through to copper black if required. Glaze 1BV11...brushed lightly over...dark blue/ grey colour. Added details can be achieved by drawing through the powdered glazes and revealing the clay body underneath. Recipe:- Basic Glaze No1B...........................% Barium Carbonate..........................20 Quartz..........................................10 China Clay...................................10 Feldspar Pottash...........................55 Dolomite.......................................5 Glaze 1BV1 add:- Plus..Manganese Dioxide...............8 Glaze 1BV11 add:- Plus..Vanadium Pentoxide............3 Plus..Red Iron oxide....................1 Recipe:- Basic Glaze No2B.........................% Barium Carbonate........................30 Quartz........................................10 China Clay..................................10 Feldspar Pottash..........................45 Dolomite......................................5 Glaze 2B1 add:- Plus..Vanadium Pentoxide...........1 Plus..Copper Carbonate..............3 Recipe:- Basic Glaze No50.........................% Feldspar Pottash..........................47 Cornish Stone..............................23 Whiting.......................................18 China Clay.................................12 Glaze 50X add:- Plus..Titanium Dioxide...............6This formula and method of working can be applied to all the pieces of ceramics in the exhibition, many have had their base glaze sprayed on first, and each glaze has it's palette of added glaze mix colours. There are too many to include here, but if you wish to know more please CONTACT me.
What were your glost firing packing techniques?
To achieve successful glost firing results that could be consistently relied upon, a new strategy was created where all the pots chosen for the next glaze, were positioned inside the kiln and marked in their exact placings, numbered and then removed to be decorated. Now this might sound time consuming, but in reality it saved much time and effort and avoided accidental damage to the soft glaze powder on each pot. The reasoning behind this strategy lies in the understanding of needs when firing by gas together with an appreciation of how the flow of flames, (and their reducing effects), should move throughout the chamber in the most beneficial way. With the added advantage of using silicon carbide shelving, (which are generally much stronger and proportionally thinner than alumina batts), staggered and irregular structures were quite safely created. This meant, for example, that large bowls could be positioned overlapping one stack and encroaching into the space of another, at the same time with other forms positioned very close underneath the bowls curve. This maximised the available space within the chamber and at the same time ensured free movement of gases 'licking the pots' throughout the kiln. Where necessary extra props and small cut pieces of thin alumina batts were introduced to place smaller objects to fill gaps, to ensure an even balance of pots to space in the chamber too. With each firing a quick sketch was made of the planned layout and it's success checked against the final result for future reference.
How did you control a glost firing in a 'reducing atmosphere'?
The following information is really only set out as a brief guideline, as an aid to understanding the processes involved in firing by this technique. For a much more detailed breakedown of the whole business please CONTACT me.
The key element of understanding the method of glost firing in a 'reduced atmosphere' can very briefly be explained as follows :- Towards the end of the glost firing a process of cutting back on the oxygen supply in the chamber by various means is introduced. Initially with this particular kiln at around 1050 degrees centigrade the Secondary air port at the base of the chamber is closed, and the damper at the bottom of the chimney is pushed in a touch. This introduces a secondary reduction. My particular kiln has four 'Amal atmospheric injectors' which allow adjustment at the injector where the gas and air mix, and after about 40 minutes when the temperature has increased to around 1150 degrees centigrade the primary reduction begins. I have never gone in for heavy reduced effects, which is very easy to do, but the results can look dull and overcooked. Light reduction requires care and experience helps, but I do recommend the following aids:- ....... An analogue temperature gauge reading from a thermocouple placed through the roof of the chamber, compared with a digital temperature gauge reading from a thermocouple placed the kiln side above the baffle wall and between two burner ports. The digital readings are far more responsive to changes in the chamber, and offer a clue as to what is happening inside once the reduction has started. Besides this there are placed, in full view through the spy hole in the kiln door, several test rings of one of my clays dipped in a traditional Celadon glaze. At optimum times one can be pulled out of the furnace, and wearing welders goggles, thick long leather gloves, leather apron and handling a heat resistant stainless steel rod, the ring is hooked out and immediately dropped into a steel bucket of water. After the fizzing has stopped moments later it can be handled and studied. Celadon is a traditional reduction fired glaze with definite characteristics, it is also translucent and so much can be gained about what is happening inside the chamber and acted upon quickly. Beside the test rings are three Orton temperature cones - number 8,9,10, and in my opinion these are a far better guide than temperature gauges as to the precise temperature and melt conditions inside the chamber. So although my two gauges might say 1240 at the top and 1260 degrees centigrade over the burners, they should only be a guide as to the stage in the firing plan you are at. The damper at the base of the chimney plays an important part at this stage, because it controls the flow of gasses through the chamber, and opening or closing it by an inch or 25cm can have great effect. I have always favoured using two HTI white bricks cut to fit side by side, and both marked with horizontal lines to show their exact position inside the slot. They last much longer than kiln shelves, and having two prevents cracking down the middle. Potters will talk with relish about the back draft effect of closing the damper in, which can be seen when you remove the plug covering the inspection hole on the kiln door. But be warned flames can shoot out up to 12inches and 30cm in length, and many an eyebrow has been singed. This for me was unnecessary and harmful to my glazes, in fact if anything I would look for an even balance of pressure. Experience does play it's part and this is where note taking is so important. My studio is on a hill and this means that the kiln firing was subjected to all sorts of atmospherical changes, some of which could have a tremendous effect on the flow of gasses through the chamber, and this even with a twelve foot chimney placed on top. Towards the end of the firing and the end of the reduction period I am looking at the cones through the spy hole, having pulled out all the test rings. Beside the cones one gets to know and see a familiar ethereal flow in the gasses licking the pots. A study of the colours, density and flow of these gasses can be very useful in understanding and controlling the fire. Sometimes after cone 9 was starting to bend the top temperature would be held, and a short period of soaking would take place, it's time length depended on which base glazes were being fired. Then when cone 9 was down and cone 10 was just starting to move a fraction, the kiln would be turned off after about 7.5 hrs, and left to cool down and be opened, the fun part, a day and half later. Always there would have been a few colour experiments thrown in on small bits of pot just to keep the interest going.
For me the excitement of making my own pots in this traditional manner, albeit somewhat updated, has been the challenge and appreciation in finding ways of responding to the elements not only in terms of handling clay in all conditions, but also responding to firing this kiln in all weathers, and I have loved every minute of it.