Kiln Cleanliness

Problems with finished pieces can be caused by an untidy or dusty kiln interior.  Pieces can be affected by devitrification or specks of refractory material in or on the fired project.

Dust is a common problem.  Kiln wash, fibre papers and combustion products all produce particles that are collectively referred to as dust.

Vacuuming the kiln regularly is a good practice to keep the dust down.  It is best if the vacuum has a variable suction control to avoid damage to the refractory materials which make up the kiln.  It is best to use a brush attachment rather than the bare hose.

Dust on the brick or fibre board floor of kilns can be vacuumed easily if you remove the shelf.  Usually you need to use the most suction available to pick up heavier particles such as glass frit along with the dust that accumulates on the floor.

Dust also accumulates on the sides and top of the kiln too.  If you have brick sides and tops, you can continue to use the high suction.  You need to be careful around the elements so that you do not bump them.  This is where the brush attachment is most useful, as you can gently brush out any accumulated dust and any loose particles from the brick.

If you have fibre sides or top, the high suction setting on the vacuum will pull fibres from the refractory material.  You need to use a low setting to avoid damaging the insulating materials.  Gently pass the brush attachment along the insulating fibre and along the elements.

This vacuuming of the kiln does not need to be done on every firing, only at regular intervals.  It is also a good time to check the condition of the elements and condition of the interior of the kiln.  Any element tail connections can be checked for tightness.  The condition of the bricks can be checked as you vacuum. 

Of course, if you are going to fire an important piece, it is a good idea to make sure the kiln is clean before you start. But daily cleaning is not required.

It is not only the interior structure of the kiln that needs to be clean.  You should be checking the cleanliness of your kiln furniture too.  Make sure you keep the shelves dust free and regularly kiln wash them.  Check the kiln posts for flaking kiln wash and dust.  Clean off any dust or loose material and re-coat as necessary.  

And while you are doing all this cleaning, you could vacuum the outside of the kiln too.

Kiln wash

When considering how many layers of kiln wash to put on shelves, especially in melts, combing and other high temperature operations, you need to remember what the kiln wash is doing – what its purpose is. 

Kiln and batt wash, shelf and mould primer are all different terms for the same thing – a separator between the glass and the kiln furniture or mould.  The amount needed is enough to completely cover the shelf. This is usually 4 coats - one top to bottom, one side to side, one each diagonal.  If you are spraying the kiln wash, use a coloured kiln wash to help ensure coverage. The shelf is adequately covered when the shelf is a uniform colour although a sense of the original remains while the kiln wash is wet.  Additional coats do not provide additional protection. The disadvantage of thick coatings of kiln wash is that the excess tends to stick to the glass as it is lifted from the shelf or mould.

This post gives guidance about the methods for application of kiln wash.

Multiple firings of kiln wash

Batt Wash Sticking to the Glass

The main reasons that kiln wash sticks to glass are:

1. Firing at too high a temperature. The higher the temperature, the more likely the kiln wash will stick to the glass.

2. Firing with opalescent glass against the shelf. Kiln wash sticks to opalescent glasses more easily than to transparent glass.

3. Re-using kiln washed shelves that have been to fusing temperatures already.

4. Using kiln wash with high amounts of china clay makes for more sticking. Thus some brands stick more frequently than others.

Firing at too high a temperature is probably the worse culprit. The second is using opalescent directly on the kiln shelf.


Strategies to avoid this sticking are:

1. Fire at the lowest temperature you can to get the result you want. This often requires slow rates of advance and extended soaks at the working temperature

2. Use Bullseye kiln wash. It is among the best.

3. Have a transparent glass as the bottom layer.

4. Use iridised glass, with the iridised side down to the shelf, as the iridisation acts as a separator. Do not do this with Thinfire, as it can lead to large cavities in the glass.  Fire onto kiln wash.

There are ways to get the kiln wash off but it's easier to avoid it. Using an iridised sheet on the bottom is probably the most effective prevention.  

Multiple firings of kiln wash

Removing Kiln Wash from Shelves

There are at least three ways to remove kiln/batt wash from mullite kiln shelves.

One quick way is to use a broad wallpaper scraper held at a very acute angle to the shelf. This rapidly removes the separator. One down side to this method is that any uneven pressure can put a gouge into the surface of the shelf.

So a more gentle way to remove the wash is to use a drywall/plaster board sanding sheet or other open weave sanding material. This allows the powdered wash to come through the sanding material rather than clog up the material. The disadvantage to this is that it takes longer to remove the wash, although it does leave a very smooth shelf after many sandings.

A third way is to wash off the kiln wash. This is relatively quick, but it gets the shelf wet and requires a longer period before the shelf becomes dry. You can, of course put the next application of kiln wash on as soon as the shelf is clean. They both can dry off at the same time.


Power tools used to clean kiln wash from the shelves can induce low points in the shelf which will promote bubbles during fusing.  It is recommended to avoid power tools in removing kiln wash.

Smooth Kiln Wash on Shelves

There are a number of ways of applying separators to the kiln shelf.
These go by a variety of names - kiln wash, shelf primer, batt wash, etc. - all are separators to keep the glass from sticking to the shelf. They are all combinations of alumina hydrate and china clay (or kaolin or EPK) in various amounts.  The china clay provides a high temperature binder for the alumina hydrate which does not stick to glass.

These are some examples of glass separators.  The Primo Primer has very little china clay, and is easy to remove.  It is particularly good for small casting moulds.

    

The object in applying the separator is to achieve a smooth surface a possible. Remember there will always be some texture because of the particle size of the wash.  For the smoothest surface, use the finest powder you can find.  You can, if you want to spend the time and effort, put the powder into a rock tumbler with ceramic balls to get an even finer powder.  Avoid shelf primer that is intended for ceramics, as it is coarser than that sold as a separator for glass.

It also is important to prepare the mixture some hours before application to ensure all the particles of the powder are wetted.  Immediate use often leads to a gritty surface.

There are several methods for applying the kiln wash to the shelf.  The two I use are spraying and brushing.  Which I use depends on circumstances - spraying requires more set up time.


Spraying the separator onto the shelves can give an even coating without brush marks, runs or ridges.  In this example a mould is being sprayed.  To ensure an even covering on a shelf, it should be horizontal and leveled so the kiln wash is evenly distributed.  Numerous light passes with the sprayer is best, as in air brushing.

Applying the kiln wash with a very soft brush such as a hake brush in a variety of directions will ensure full coverage. 

The brush should lightly touch the shelf and provide a number of thin layers.  Applying in four directions - horizontal, vertical, and the two diagonals will ensure full even coverage. There may be some residual brush marks.

To reduce the application marks further, you can brush or spray hot water over the still damp kiln wash. This helps to remove brush marks or the stippling that often comes from spraying and brushing.  It is important that the shelf is perfectly level for this operation.


Another way to reduce the texture after the shelf primer dries is to lightly polish the kiln wash with a ball of old nylons or rub a flat piece of paper with the palm of your hand over the shelf.  Be sure to remove the dust that may be left behind from this polishing.


Boron Nitride

Another separator that has become popular in spite of its expense is boron nitride, often referred to by the trade name Zyp.  This is a high temperature lubricant for industrial kiln operations that has been adapted for the generally lower glass forming temperatures.  This is not suitable for kiln shelves, as it completely seals the porous surface of the shelf.  It is difficult to go back to the cheaper kiln wash separator as the water of the kiln wash solution will not be absorbed into the shelf, leaving a patchy coverage of the kiln wash.  Although both separators should be renewed after each firing (above low temperature tack fusing) the boron nitride is much more expensive and cannot provide a smoother surface than the shelf already has.  My recommendation is that boron nitride use should be confined to moulds or other surfaces where the glass may slide or move in the forming process.

Cleaning the Kiln of Dust

Dust is promoter of devitrification. You should do the most you can to keep your kiln free of dust.

Dust can come from the kiln lining materials.  Regular gentle vacuuming of the kiln surfaces will help prevent particles from falling on to you work or other surfaces in the kiln.

It can come from the separators you put in the kiln.  I often see pictures of used fibre paper at the side, or under, the kiln shelf.  This should be cleaned out after each use to provide clean firing conditions.

The main reason for this obsessive cleaning is that dust particles within the kiln will be disturbed by the air movement involved in closing or opening the kiln lid or door. There also is air circulation within the kiln during the heating and cooling phases, although it is not as much as when opening the door/lid.  These disturbed dust particles will settle on the glass and defeat your cleaning of the glass.  

Glass Stuck to Element

First consideration you need to think about when you discover glass stuck to an element is the nature of the metal of the elements.  Once fired, kiln elements become brittle.  This means that they are likely to break if disturbed when cold.  So, you need to make sure you absolutely must do something to rescue the kiln.  It may be that you can just leave the stuck glass alone.  Where the glass is, and how much of it, is stuck to the elements is important when considering what to do.

Where

This brittleness of the elements means that the location of the glass in relation to your firings needs to be considered.  If the glass is on an element below your normal firing position, you can think about just leaving it.  This applies to glass stuck to the side elements too, unless you are in the habit of firing very close to the side elements. The heating elements of the kiln form an external layer of oxidisation that protects the inner metal.  This means that small amounts of glass will not affect the operation of the elements, nor your future pieces.

If the glass is stuck to top elements, you are likely to be more concerned about future drips of the glass onto your future work.  The glass is not likely to become hot enough to detach or drip onto your work except at extended full fuse or casting temperatures.  This means that you can observe the progress of any possible drip at each firing and only remove the glass when it begins to begin to hang down from the element.

How Bad

How much glass is stuck to the element?  Normally, if it is only a small amount, it can be left.  Ceramics kilns often have a bit of glaze (a glass carrier of the colour) stuck to the elements and continue to be fired for years without damage.

If there is a lot of glass stuck to the elements you will need to remove most of it to avoid dripping onto future work. 

Methods of Removing

In most cases where there are significant amounts of glass stuck to the element, it is on the brick or fiber lining of the kiln too. 

My recommendation is to heat the glass just a few centimetres from where it is attached to the element. Use a hand-held blow torch to do this. When the glass is red hot - enough to begin moving - you can pull it away between the lining and the element with long handled tweezers.  Do not attempt to pull it off the element right away.  You can later chip the glass off the lining without damaging the element as the connection is separated.

As the element has begun to be warmed by the heat used to separate the glass on the lining and the element, you can continue to warm the element, moving the torch in a slow waving motion at least 10cm each side of the stuck glass.  When the glass and element are red hot, you can begin to pull the glass off with long handled tweezers, bit by bit.  Keep re-heating the element and glass as much as necessary so the temperature does not drop below cherry red.  This ensures the elements continue to be flexible and will not break.

Of course, glass can be melted onto its kiln furniture and there are different considerations for those circumstances.

Kiln Washing Kiln Lids

It is frequently recommended that the bottom of the kiln should be kiln washed to prevent any spilled glass from sticking to the kiln brick.  You should remember that this is applicable to brick lined kilns.

This in itself is a little clue.  You do not need to kiln wash any insulation fibre in the kiln. If any glass were to stick to the fibre, it would come away easily.  In any case, most insulation fibre blanket will not stick to the glass.

The recommendation often goes on to advocate kiln washing the sides.  There is a caution that the side elements (if any) should not be kiln washed. The caution comes from the knowledge that water and electricity should not be mixed.  The kiln should not be on when applying kiln wash anyway.  If kiln wash is splashed onto the elements, it is simply a matter of letting the whole kiln dry naturally with the lid open before firing.

The extension to this series of recommendations is that the whole of the kiln should be kiln washed, including the lid.  This is not a good idea.  The wash on the lid will soon fail and drop dust and debris onto and into your work.  The glass should never touch the top of the kiln anyway.  If the elements are in contact with the glass, the glass will either stick to them or break.  You have to ensure you do not put glass nearer than about 20mm to the elements or lid. In any case, the glass will fall to the bottom of the kiln, not the top or sides – unless the kiln is not level.

BUT

The whole idea of kiln washing the interior of the kiln is suspect in some ways.  Anyone who has had glass drip off the shelf and onto the brick during an over-firing will know the glass eats into the brick through the kiln wash.  Kiln wash will only protect the brick at full fuse or less temperatures. But it is a good precaution to keep the pieces of frit that fall off the shelf from sticking to the brick. It does not do much more than that.

The application of kiln wash to the kiln creates another source of dust within the kiln.  Dust and general uncleanliness in the kiln is a main potential source of devitrification. Thus, the application of kiln wash should be the minimum necessary and does not need to go up the side beyond the elements or the lowest shelf height, whichever is less.

There is a strong argument to be made that laying a sheet of 0.5 mm fibre blanket on the floor of the kiln will provide better protection of the kiln than any amount of kiln wash.  It is less likely to fail, it is not a source of additional dust, it provides a better protection during any kiln runaway, and it is easily replaceable.

Spacing of Pieces on the Shelf

It is natural that we should want to put as much onto the shelf as we can to maximise the number of pieces from each firing.  But, when you are placing the pieces remember that glass expands as it heats up. When the glass is at its maximum expansion, it will be much less viscous than at lower temperatures and so will stick very easily to any neighbouring piece it touches.

Although the final size of a two-layer piece is the same at the end as the beginning, they do expand to a larger size during the fusing process.  My experience shows me that a 6mm piece can expand as much as 5mm, depending both on temperature and size.  This means that I treat 10mm as the absolute minimum space between pieces. But, because of the size of my fingers, my normal minimum placing is 20 mm apart as that is a comfortable space between my fingers and the other glass.

Thicker pieces expand to become larger after fusing than they were at the start. These pieces spread more during the firing than the 6mm piece.  A 9mm piece may expand by about 3mm at the finish – depending on size and temperature.  But during the firing, it may expand as much as 9mm. This means that 20mm is an absolute minimum between pieces that are 9mm thick at the edges, even though they may be only 6mm over most of the area.

The tip is to avoid over-filling your kiln shelf.  By trying to get too much production in one firing you may find a number of pieces stuck together at the end, thus eliminating any savings on glass or space. 

Baffles in Side-Fired Kilns

The object of using baffles in side fired kilns is to keep the direct radiant heat from the edges of the piece(s) being fired.  If the edges receive direct radiant heat, they increase in temperature more rapidly than the interior of the piece.  This means the edges become sticky and seal before upper layer of the interior begins to conform to the lower layer.  This seals air into the piece.

fusedglass.org

The materials and placing of the baffles is important.

Baffles can be made from almost anything that can withstand the heat of the firing.  There is an argument that light-weight materials such as fibre board, vermiculite board, or fibre paper should be used to reduce electricity costs.  Heavier pieces such as brick and kiln shelf pieces require more energy to heat them up.  They then of course, store heat that needs to be released on cooling, so slowing the cool down and increasing the risk of devitrification.

The placing of the baffles is important too.  Baffles protect the glass edges from radiant heat until the general heat of the kiln can come into effect over the whole of the piece.  This means that if the baffles are placed against the elements at shelf level, the element above can still give radiant heat to the edges.  Therefore, baffles placed near the glass are better.  They protect the edges from radiant heat at whatever level the side elements are placed.  This is more important for pieces that are further from the edge of the shelf, than those nearer the edge, as the centrally placed glass can “see” the radiant heat from the upper elements. 

Making Tests

Every time you get a kiln that is new to you – whether new or second hand – you need to do some tests. Recording these tests is essential to your future work.

The first test is to get to know your kiln – where are the hot and cool spots, what effect does the kiln produce at a given temperature and soak. A very good guide to knowing the temperature differentials in your kiln is given by Bullseye Tech Note 1 – Knowing Your Kiln 

The second test is to make a series of small scale tiles to know what your kiln does at different temperatures and rates of advance. What combination of rate and temperature gives the roundness, degree of tack, flat fuse that you want.

How does the kiln perform in slumping and what are the effects of thickness and number of layers on the rate of slump.

These are elements that you may feel are a delay in being able to experience the enjoyment of fusing. However, they are essential to the long term enjoyment and success of your fusing activities.

First Firing

Even if this is not your first kiln there are a number of things to do when starting.

The first is to read the manual. Obvious, but in our enthusiasm to get started, reading seems boring. It is essential to understand what the manufacturer wants you to do and to understand how the kiln and controller work.

Then, you can prepare kiln. Test fire the kiln empty to make sure it works and burn out any binders remaining in the kiln materials. You can do this firing at about 400C/hour as there is no glass to damage. Fire to around 800C. Then you can shut off, or programme a dummy anneal. This also ensures you know how to work the controller.

While waiting for the kiln to complete the fast test firing, read the manual again.

When the kiln is cool, apply kiln wash to the bottom (if it is brick) and lower sides, below any side elements. If the bottom or sides are fibre, no kiln wash is required. Kiln wash the shelf and any kiln furniture too.

Now is the time to test for how even the heat is in your kiln. Arrange the kiln furniture around the shelf as described and put glass over. The kiln furniture can be any refactory material, even folded 3 mm fibre paper will be strong enough to hold the small pieces of glass above the shelf. Fire the kiln as described in the Tech Note 1.

Now try out the suggestions in the manual, especially the programming of the controller, even if it has pre-programmed schedules. Look at Bullseye and Spectrum sites to get sample schedules. Enter these as trial schedules.

Then you should be ready to fire the first piece of glass. Place the glass in the kiln, programme it, and record the information about the firing. Now turn the kiln on for the first real fuse.

Applying Kiln Wash

Kiln wash, or batt wash as used in the ceramics field, is largely made up of alumina hydrate, kaolin (china clay), and often some colouring to indicate an unfired shelf.

These solids are heavy and settle to the bottom of the container quickly. So, you have to agitate the contents with each dip of the brush onto the liquid. To provide adequate - and even – coverage of the shelf, mould or other refractory material, you should paint in four directions. Up, down and the diagonals. You need to apply just enough that you do not see the shelf surface.

Alternatively you can spray the solution onto the surface. This is an easier way to get an even covering, but it sometimes is overly stippled.

A tip I was given for the smoothest kiln shelf is to level the damp prepared shelf and spray a layer of warm water over the wash to form a very shallow puddle. As the water is absorbed into the shelf, the only limitation to the smoothness of the surface is the granular nature of the kiln wash.

Writing Your Own Schedules

Most introductory kilns are now being supplied with pre-set schedules. This can make moving on to the schedules you need for the new work you are doing appear to be difficult.

The first thing is to get the print-out of the pre-programmed schedules and determine what each stage of the programme is designed to achieve. If you compare the programme temperatures with a description of what is happening with the glass at that temperature, you will be going a significant distance to making your own schedule with an understanding of what you will be achieving with each stage of your purpose made schedule. A very good guide to what is happening to glass at various temperatures is this note from Bullseye. This also has the advantage of telling you what happens with different thicknesses of glass.

Next compare the pre-programmed schedules with those printed on the manufacturer's website, for example:

System 96

Uroboros

So, now you know what temperatures you are trying to achieve, how fast should you go to get to that temperature? I have developed a guideline that the initial rate of advance should be no more than twice the rate of your initial cooling rate for the final piece. This means that you start planning the schedule from the annealing portion of the full schedule. If you will have a final flat thickness of 6mm, the annealing rate will be around 80ºC, so the initial heat up rate could be about 160ºC. This is a conservative rate, and experience will guide you to how much quicker you can heat up the glass. This initial heating phase can be all the way up to the bubble squeeze/ slumping temperature, but must be to a temperature at least 40ºC above the annealing point.

There are at least three elements that will reduce this initial rate to less than this general guidance: Thicker pieces need more care. The more layers, the more difficult it is to get the heat to the bottom layer, so slower rates of advance are needed. The greater the unevenness in thickness, the slower the rate of advance.

There are, of course many other variables relating to the kiln, some of which are:

Side or top elements

Distance to the elements – side or top

Distance to the sides of the kiln

Placement in the kiln – e.g.,floor or shelf and how high

Nature of the firing surface – e.g., ceramic, fibre board, fibre paper

Placing in relation to the hot and cool spots in the kiln

How the glass is supported - especially on a slump or drape

At the initial stages of learning about fusing schedules, you need to make notes of all these things (and the results) on your firing records so that you can refer back to get guidance on what rates of advance are acceptable for any given firing.

Part 2

Kiln maintenance

Before or after each use

Vacuum the inside of the kiln. Use a low suction setting, especially on fibre walls and ceilings. Stronger suction is possible when cleaning the brick floor.

Check on the kiln furniture – including shelves, boards, supports. Are they kiln washed and without scrapes, scratches, gaps? Has the kiln wash been fired to full fuse temperature?. In both cases, clean the used kiln wash off the shelf and renew.

Check that the shelves and other kiln furniture are without cracks.

Clean kiln furniture of dust and debris.

Check the level of any item placed in the kiln, e.g., mould, with a spirit level.

Example of a small 2-way spirit level

Monthly

Electrical parts: check the elements and their connections (normally at back or side). The screws on the connectors for the element tails should be tight. If they are badly corroded , they need to be replaced.

Any support pins or wires should be firmly seated in the brick work or supported by sound hangers.

Check the level of the kiln and internal shelves on a a regular basis and every time the kiln and its internal furniture is moved.

Glass Shifting on Mould

There are a number of things to investigate if your blank is shifting on the mould during firing.

Is there a heat differential?

Glass absorbs heat at different rates depending on colour and type meaning that one part may begin to move before another. The solution to this is to slow down the rate of advance to allow all the glass to gain heat at the same speed. It may also be useful to slump at a lower temperature.

There also may be a heat differential within the kiln. You need to run a check on the heat distribution of your kiln to be sure where the (relatively) hot and cold areas of your kiln are. Bullseye published Tech Note no.1 on how to do this.

Not perfectly balanced on the mould?

Glass can be placed just off square or level and that can allow it to start slumping unevenly. Measurements and observation can help to get the glass placed squarely on the mould. Also a small spirit level placed on the glass can tell you if the glass is level within the mould.

The mould may not be level.

The kiln, shelf and mould should each be checked for level in all directions. The kiln level can be established and can be assumed to be level until it is moved. The shelf level should be checked each time it is moved. The mould level should be checked each time it is used.

Is the glass overhanging the mould?

Glass overhanging the mould rim can hang up on some of the edges more than others. Check the rim of the mould for any rough areas and smooth them. If you do have glass overhanging, you should slow the rate of advance to allow the edge of the glass to tip up and begin to slide down into the mould. If the problem persists, make the glass blank smaller, or support the overhanging glass with a collar.

Is the glass heavier on one side?

The glass may be uneven thickness and so heavier on one side. The heavier area of the glass will begin to slump first and so promote movement of the whole glass in an asymmetrical manner. The solution to this is to fire slower and to a lower temperature.

Do you have a wonky mould?

The mould can be imperfect. So you need to check the mould for accuracy. I have a slumper that has one side lower than the other three. Being aware of this, I can place the glass so that it is still useable. Measuring the mould in all directions will help determine its symmetry.

If all these things have been investigated and the solution not found, it is possible to create a bevel on the bottom edge of the glass so that the edge sits in the mould at the same angle as the mould. This provides a larger contact point for the glass and mould than just a thin edge. This appears to allow the glass to move evenly during the slump.

Of course, a major solution is to observe the slump.  Peeking into the kiln at the beginning of the slump soak and frequent intervals after that will show if the piece is slumping evenly or not.  If it is uneven, you can put on the appropriate protective gear and with gloves on your hands, shift the glass to be set evenly in the mould.

The major solutions to avoid uneven slumping are:

• Avoiding the hot and cool parts of the kiln
• Making everything level
• Careful placement on the mould
• Slower rates of advance
• Lower slumping temperatures
• Observation

Using Space on Shelves

Often there is unused space on the kiln shelves when you are firing a project. With a bit of planning, you can make use of the spaces for a variety of things.

Frits fired on fibre paper

Bowl made from frit balls

You can place piece of frit in the clear areas to make frit balls.

You can make colour tests on plaques of glass to see the results of strikers, powder combinations or results of various depths of colour.

Compatibility tests can be done with pieces of glass of which you are not certain.

simple stress testing set-up

Strip of fired glass samples for testing

Results - those with halo are stressed

In the same way, annealing tests can be conducted.

You can fire small pieces of jewellery at the same time as your larger pieces.

You can also prepare elements for incorporation into other fusing projects and lay them out in the open spaces on the shelf.  Your use of the spare space is related both to your imagination and to your future projects.

Installing Your New Kiln

You have your new kiln unwrapped. Now where to put it?

First read the manufacturer's recommendations. If you are still uncertain there are a number of things you should think about.

One of these is getting access around it. You need to be able to work around three sides ideally if it is a top loader, two sides for smaller kilns is usually enough. If it is a front loading kiln you only really need to consider the space in front of the kiln. You are going to be carrying pieces, even shelves to the kiln so you need enough space for you and the shelf in front of the kiln. At the sides you only really need enough space for yourself.

Getting access is part of the consideration of distances from other things. Often people are worried about the heat that the kiln will be giving off. Kilns are well insulated to reduce the costs of firing, so the heat release is slow. Still, you want at least 300mm space from anything inflammable.

You also will want to think about the support surfaces. Sometimes the kilns come with their own stands, but usually these are to raise the kiln to working height. You may want to protect against any (unlikely) meltdowns, so you should put the kiln on steel, ceramic or concrete surfaces. There are a number of table top models and in these cases a large ceramic tile or ceramic fibre insulation under the kiln is an entirely adequate safety precaution.

You will need a place to put things down just before loading the kiln, so placing the kiln near adequate flat surfaces is important.

You also should think about putting the kiln out of the main traffic areas of the studio to avoid disturbance to the kiln or the rest of the studio activity.

Now that you have the ideal location for the kiln you have only begun.

You need to make sure the kiln is as level as possible. The first stage of this is to make sure the casing is relatively level. Use of a spirit level on the top front and sides is probably enough. Put hard spacers under the legs to level things up. You can if you want, level the internal base of the kiln instead of the casing. Many find that more re-assuring. Then you need to put the kiln furniture to hold up the kiln shelf into the kiln and the shelf on top of that. This is the part that really needs to be level. Spend time on it. Place pieces of ceramic fibre under the shelf supports as required to get things really level. A circle or three-way level is good for this purpose. The shelf needs to remain level to get good, consistent results. Any time you move the kiln, the shelf, or the supports, you need to check the level of the shelf.

Once you have the shelf level you are ready to do a test fire. Normally you need to have a firing without anything in it to burn out binders used in the making of the kiln. There is no reason that you cannot have the furniture (shelf and supports) in the kiln for this first firing as they need to be test fired too. In addition you can run a test to discover where the cool spots are in your kiln (every kiln has them). Look up and follow this technical note on how to run a test for discovering how even the heat is within your kiln.

Once you have run your test firing, you will want to protect the kiln floor from any spills of hot glass and the glass from sticking to your furniture. If the manufacturer has given you some kiln wash with the kiln mix it up about 1 part powder to 5 parts water and lightly paint the floor of the kiln - not the walls. The kiln furniture needs this too as does the shelf. This note on applying kiln wash will give you information on how to do it. 

It is important that you have some protective gear to do the work with kilns. At first and for fusing temperatures, you need eye protection and gloves. You need to look frequently and briefly into the kiln to monitor the firings, especially at the start of your career. For this you need eye protection. Sun glasses will not do as you need protection against infrared rather than UV light. There are a number of things that will do from welders' goggles to special lenses as used by bead makers. Use them! Every time. You will need gloves, at the start leather gloves with sleeves going half way up your forearm (such as welders' gloves) will do. Later and for higher temperature work you will need better and much more expensive gloves, sleeves, and body protection.

These things will get you off to a good start.

Brown Ceramic Fibre Paper and Board

A frequent concern about fibre board and fibre paper that appears brown when peeking into the kiln is that something has gone wrong.

Ceramic fibre papers and boards have organic binders that have to burn out during the firing. What starts as white later turns brown as the binders are burning out – often the smell is like burning paper. As the binders burn away, the fibre paper or board returns to its original colour.

The amount of smell or smoke is dependent on the amount of ceramic fibre you have in the kiln. If you have a thick board, you should think of venting the room, as there will be a lot of smoke.

Also if you are firing a large piece of glass, you should think of firing the binders out of the ceramic fibre before placing the glass on top. If you do not, the binders may not fully burn out, leaving marks of the smoke fired into your glass.

Placement of Pieces for Firing

Placing pieces in the kiln, especially in oval and side fired kilns, is not about filling the kiln completely. Kilns have hot and cold spots, and the arrangement of the elements can have an effect too.

The first thing to determine with a new kiln - and immediately after any alterations to the kiln - is where the hot and cool areas of the kiln are. There is an extensive guide to this on the Bullseye site. In short, the method is to place strips of glass on short kiln furniture all around the kiln at the level(s) you will be firing. These strips should be of equal size and the kiln furniture the same distance apart. Take the temperature slowly up to slumping temperature. Observe when the visible glass pieces begin to slump. Let that continue until they are about half way down. Then proceed to the anneal. When cool you can open the kiln and see the areas where the glass has slumped most – the hotter areas – and where it has slumped least – the cooler areas. This will give you information on areas to avoid if you want an even finish all around the edges.

If your kiln is side fired, you need to consider the shelf placement in relation to the elements. The best arrangement is to have one element below the shelf and the shelf between elements so the radiant heat is not directly onto the edge of the shelf as that may lead to breaks.

Put glass on the shelf as centrally as possible. If the glass must be near the elements, baffle the glass from the direct radiant heat from the side elements.