The Basics of Using Clay - Kilns – Glazes – Cones – Firing
Kiln Furniture Prep
Read your kiln manual(s) first.
Kiln Wash - This layer of protection prevents glaze from sticking to the shelf when it drips from a piece of bisque. With the coating of kiln wash on the shelf, the glaze can be scraped off easily. The powdered kiln wash has an unlimited shelf life so it can be stored and used later. Once every six months to a year, or more if your shelves show unusual wear, scrub off the wash and apply fresh wash.
Mixing up kiln wash
Make kiln wash using ¾ cup water and adding several tablespoons at a time of powder kiln wash INTO the water (not the other way around!), mixing with each addition of powder, to form a very thin creamy paste the consistency of milk. Yes, you may have to add more water, as well, especially if you are mixing up more than one bag of wash and kiln-washing more than 8-10 large half shelves.
Use a designated KILN WASH brush – a 2”-3” synthetic bristle brush and apply one solid coat to one side only of kiln shelves. Take the wash out to within ¼” all around the edges of the shelves. Allow shelves to dry. Store extra kiln wash in marked, airtight container for future touch ups and use. *Store shelves kiln wash sides to each other.
Loading and Unloading the Kiln
Set the four shortest posts (1/2 or 1” inch) in a triangle pattern if using half shelves or a square pattern if using full shelves inside on the bottom of the kiln.
Set shelf on top, with kiln wash side up. If 2 half shelves, leave 1/2” space between shelves for air flow.
Always use cones – more details on this in each below section.
Always log firings on Log Sheet. If ANY piece has a problem, always save cones and be sure to designate shelf they came off of for reference.
Always read Firing Sheet to be sure you are properly pushing the correct buttons for a firing. Always press Program Review to make sure you did indeed push the correct buttons.
Never turn the kilns on if someone is not going to be at the house or studio at or about the time the kiln should turn off.
Never turn the kilns on if in the middle of a storm and the electricity continues to go on and off.
Always stilt glazed pieces with low fire pottery.
Always leave 1” space between pieces.
Always leave 1 ½” space from top of tallest piece on any shelf to shelf above it.
Always check stilts to be sure pins are free of glaze from previous firing and are still straight up.
Always check stilts when unloading. Use stilt stone or Dremel off any glaze – be sure to wear safety glasses when doing so.
Always put correct posts and stilts back in their corresponding bins.
Do not take cones out of boxes until you are ready to use them. Always keep cone boxes closed when not in use.
After turning on kilns, if venting, flip in-line switch on vents to turn them on during firing.
*Watch out for the thermocouple – DO NOT BUMP IT WITH THE SHELVES WHEN LOADING AND UNLOADING THE KILN.
Test Fire: There are 4 reasons to do a test fire in your new ceramic kiln BEFORE you try to fire bisque or glazes:
1) To oxidize the elements. This is also sometimes called ‘seating the elements’ firing.
2.) To temper the shelves, posts and sometimes stilts.
3) To make sure the wiring was done properly.
4) To find out the firing personality of the kiln. All kilns, just like all ovens, have some slight variations to the way they fire. Might be a bit hot, or a bit cool. Can have hot or cool spots. Can be a cone cooler on the bottom shelf.
After loading the kiln, as per above instructions, we test fire most ceramic kilns to Cone 04, fast speed. There are SOME kilns that can not fire to 04 at fast speed. You will use a set of cones - Cone 03, 04, 05 - on each of the layers. If a medium sized kiln, it may be we only put the cones on the bottom shelf and on another layer of shelves ABOUT half way up inside the kiln. Again - remember to load shelves an inch and a half ABOVE or BELOW the thermocouple. If a large 10 or 12 sided kiln, you may have anywhere from 4 to 5 layers of shelves. You will want to have a set of cones on the bottom layer, up a third and up another third. If there are other layers in between these, it is not necessary to also put a set of cones on these shelves. Some manufacturers may suggest putting an 04 cone also on a shelf closest to the thermocouple. You can do this but the other sets of cones should be placed towards the center of the kilns. We know the temperature will be hotter closer to the elements, but we need to know what the temperatures are getting to in the center sections of these kilns. If we find the bottom is firing cooler than the other sections, then we will want to add a HOLD time to the glaze firings. This may or may not be necessary on the high fire side of firings. If the bottom shelf is cooler, your oranges and reds may not mature and may be brown or not quite bright enough for you.
Do check out the Orton 3 Cone System and Understanding Cones and Temperature on these pages on our site.
Firing the Kiln - Clay Firing – turning Greenware to Bisque:
Greenware pieces are not stilted. Doing so will melt the clay body into the stilt.
Place one each of pyrometric self-supporting cones 03, 04, 05 in the middle of the bottom shelf 1” apart in a row and 1” apart from one another. Place 3 posts* in a triangle pattern on each of the 2 half shelves. Continue to load shelves, posts cones and pieces making sure the tallest piece on any shelf still has a 1 ½” clearance to the shelf above it.
Make sure that any shelf will be either 1 1/2” above or below thermocouple.
Make sure peephole plugs are in the peepholes.
Follow directions for pushing buttons on kiln. 04, Slow Speed, No Hold.
Notes: Clay – firing greenware to bisque to 04 firing, thus the 03, 04, 05 cones. Temp goes DOWN with higher “O” numbers; goes UP with regular numbers. In this clay firing, the 03 cone should stay standing, the 04 bent over to a perfect touch at “6 o’clock”, and the 05 should go limp and look like an elephant trunk.
Temp will be 1940 to 1945 degrees F. Firing will take 9 to 10 hours or longer depending on size of kiln and how full the load is. Do not go home until the kilns have completed firing.
Low Fire Clay Bodies like Laguna Terra Cotta EM215 and EM 210 White may say 04-06 on the box they come in. This means fire the clay to 04 (AROUND 1940-1945 degrees F.) to turn it from greenware to bisque. You do THIS 04 firing on SLOW speed. And then fire the low fire glazes to 06 (AROUND 1830-1835 degrees F.) You do THIS firing on MEDIUM speed.
The low fire clay body can then be painted with our low fire paints and then dipped (or not), stilted and then fired to 06, medium speed.
High Fire Clay Bodies can be Cone 5, Cone 6, Cone 8, Cone 10 Stonewares or Cone 6 Porcelain. These boxes may only say Cone 5 or Cone 6 or Cone 10 or whatever temperature that clay body MATURES at. To turn this greenware clay to bisque, you still fire 04, SLOW speed. Some people will bisque fire to Cone 06. But you do the GLAZE firing to the temperature or cone indicated on the box. See below for more details on greenware to bisque firings and glaze firings.
Keeping Clay - It is in a wet form in a bag and may look gray, buff, white or red. Usually in a loaf shape, there may be two 25 lb. bags in the box. For longevity, we recommend putting each bag into yet another bag and putting another twist tie on it. Sometimes the original bag can get tiny slices, cuts or holes and then the clay will dry out too much to be of further use. You could put a wet paper towel in the bag with the clay before you put it in yet another bag. This will help keep it from drying out or can help soften clay that seems a bit harder than we would like.
Laguna clay is pre-wedged, however you may still want to work it a bit more.
Option 1 - Using Clay
One Step Firing and Glazing for low fire clay
This is not the best method to use, but when in a pinch, you can do this. For example, project must be able to be completed in one step because you only have access to the group once.
Pull off or slice off the needed amount of clay from the loaf. Dispense to each student and have them work it in their hands to soften it. Very small amounts of water can be added to further soften it. They can then sculpt or mold the clay into the design – pinch pots, coils, beads, slabs, etc. depending on the project they are creating.
Once they have created their design and the sheen is off the clay, they can immediately put the paint on it. The only paint that can be used in this technique is Stroke and Coat. Stroke and Coat is more glaze formulated than the other brands and this makes a difference. The usual rule applies here as far as one coat is translucent, three coats will be more opaque. You must wait for the shine to go away before applying another coat. If you apply three coats you will get nice coverage.
The important trick here is to NOT put ANY color or glaze on the bottom of the piece and stay away from at least 1/16 inch from the bottom. The other important trick is that IF AT ALL POSSIBLE, do not handle the piece while painting it. Leave it on the board while they are painting. So, this would mean that this technique would work best on flat pieces like tiles that were molded and then carved into for design. If it were a pinch pot or coil pot, it would also be best not to lift it up to paint it.
The reason you don’t want to pick up or handle the piece is because clay has a memory. So if you mold it into a shape, and then handle it while wet and parts of it come out of that shape and you try to put it back, then during the firing process it will end up cracking trying to go back into one of the shapes.So….best to leave the piece alone while painting it...if possible!
Here is the cool part and why this is a one step method. After you have molded it and painted it, DO NOT DIP IT! Put it in a dust free dry area for 4-6 days, depending on the humidity in your area and how thick the piece is.
Load into the kiln using the dry foot method. That means the piece has no color, no paint, no glaze at all on the bottom and DO NOT STILT IT. As usual, you will want about 1 to 1 ½ inch between the pieces.
SLOW fire to 04, which is about 1940 – 1945 degrees. When the firing is complete and the kiln has cooled down to about 100 degrees, unload. The projects are complete.
What will the piece look like?
When there is no clear glaze put over the Stroke and Coat color and only 1-2 coats of color, the color will not look real glossy. If your students miss an area and the bisque is coming through then add some glaze to it and refire to 06 medium speed. The parts of it that got more color may appear opaque, but don’t expect it to look like our 1-2-3 coat bisque tiles that were dipped and fired.
This technique is for simple pinch pots, coil pots, beads, masks or other basic designs and these pieces are never intended to hold food or water.
And again – when you have to get it done in one step – it is a thankful option.
Option 2 - Using Clay
Two Step – This method is used when you have access to the students at least twice. As in Option 1, pull or slice off the needed amount of clay, work it until soft enough and mold or sculpt the piece.
As in Option 1, let it dry for 4-6 days depending on thickness of piece and humidity levels.
SLOW fire to 04 and dry foot. Unload around 100 degrees.
After the pieces are bisque fired, have the students paint with a 2-3 coat low fire glaze such as Mayco, Amaco or Duncan low fire glaze. Do not put ANY paint on bottom of piece. Do NOT dip.
MEDIUM speed fire to 06 (around 1830 to 1835 degrees) and do not use stilts. Again, you will not have a real glossy finish.
Option 3 - Using Clay
Two Step with Dipping
As in Option 1 and 2, pull or slice off clay, work until soft enough, mold or sculpt the piece.
As is Option 1 and 2, let dry for 4-6 days.
SLOW fire to 04 and dry foot. Unload around 100 degrees.
Paint with 2 or 3 coats of glaze. In this technique, they can paint the bottoms.
Dip once using a non-toxic clear dipping glaze.
Stilt the pieces and MEDIUM fire to 06. Critical to unload below or around 100 degrees, otherwise pieces could suffer thermal shock.
NOTE: When firing low fire clay bodies during the glaze firing – IF you have any color or glaze on the bottom of the piece, you MUST stilt the piece on the kiln shelf. Otherwise they will stick – fuse – to the shelf. But you CANNOT use stilts if putting greenware on the shelf and firing to 04. The stilts will melt into your pieces
Firing the Kiln - Firing Low fire Pottery after Dipping: Our Mayco and Duncan Bisque has already been fired to Cone 04 and is ready for low fire glazes and then fired to Cone 06.
Place one each of pyrometric self-supporting cones 05, 06, 07 in the middle of the bottom shelf 1” apart in a row and 1” apart from one another. Place 3 posts* in a triangle pattern to place half shelf.
Stilt pieces allowing 1 ½” from top of tallest piece to shelf above it. Lay down next layer of shelves.
Continue to set posts, stilted pieces and shelves until you have fully loaded the kiln.
Be sure any shelf is at least 1 ½” above or below the thermocouple. If at all possible, be sure no shelf is lined up exactly to block elements in grooves.
Make sure peephole plugs are in the peepholes.
Follow directions for pushing buttons on kiln. 06, Medium Speed, Designated Hold.
Notes: Low Fire Dipped Pottery – firing pottery to 06 firing, thus the 05, 06, 07 cones. Temp goes DOWN with higher “O” numbers; goes UP with regular numbers. In this clay firing, the 05 cone should stay standing, the 06 bent over to a perfect touch at “6 o’clock”, and the 07 should go limp and it will look like an elephant trunk.
Temp will be 1830 to 1835 degrees F. Firing will take 7 ½ to 8 hours or longer depending on size of kiln and how full the load is. Do not go home until the kilns have completed firing.
Firing the Kiln – Glass Fusing
You may have as few as 4 different firing schedules or as many as 20 or more for Glass Fusing. No matter what the piece, there will always be a Fuse Firing – Tack Fuse, Contour Fuse or Full Fuse. Then there is the matter of size – smaller than 3 x 3, 3 x 3 to 6 x 6, 6 x 6, 8 x 8, 10 x 10 and 12 x 12. The larger the piece, the slower the firing. Then sometimes, you may have a second firing for the piece – slump, sag, drop or drape. Each one of these has a different firing program. And then there is the issue of which kiln these pieces are being fired in for the effect. For these reasons, keep a completely separate Glass Firing Schedules Log. Visit our Glass Site for Glass Firing Schedules.
Firing the Kiln - High Fire Clay Bodies
With the Cone 5 clay body, fire greenware to bisque at 04 slow speed, then to Cone 5 medium speed for the glaze firing.
Cone 6 clay body - fire greenware to bisque at 04 slow speed, then to Cone 6 medium speed for the glaze firing.
Cone 8 clay body - fire greenware to bisque at 04 slow speed, then to Cone 8 medium speed for the glaze firing.
Cone 10 clay body - fire greenware to bisque at 04 slow speed, then to Cone 10 medium speed for the glaze firing.
Seeley glazes only for high fire, cone 5 B-Mix (see label!)
Some Mayco glazes can go BOTH high fire and low fire.
Amaco glazes – most are designated to go EITHER low fire or high fire. SOME can do both. Read the label.
Duncan glazes – most are low fire, some can go high fire. Read the label.