Keeping Bottles from Rolling

A common problem in firing bottles is that they may roll into one another and stick, making both bottles useless.

One way to overcome this is to let the bottle find its heavy point by setting on smooth and level surface. It will gently roll to one direction before slowly coming back in the other. When it stops this oscillation, the heaviest part of the bottle will be on the bottom.  Mark the bottle in some way so you can move to the kiln in that position. If after this, it rolls in the kiln, then your shelf is not level. 

Additional assurance against rolling is putting a small piece of thin fibre paper (1 or 2 mm)at each side of the point the bottle touches the shelf.  Thinfire and Papyros are not enough to ensure there will be no movement. But the small bumps of fibre paper are enough to stop the bottle from rolling.

Sometimes you want a particular part of the bottle up or down, but it won’t stay in place.  Then you need to put a slightly thicker piece of fiber paper against the bottle on each side.  It is better if it is not Thinfire or Papyros as they tend to disintegrate above 400C, long before the bottle begins to distort enough to keep it in place.

Other materials you can use to prevent the bottle from rolling are crumbled chalk, whiting, kiln wash, or even a few grains of sand.

Preventing bottles from rolling in the kiln is about finding the natural heavy spot, or propping the bottle in place with a variety of heat resistant materials.

Long Annealing Soaks

You Can’t Anneal Too Long.

Can you anneal too long?

Yes, you can.

It’s not just the possible temperature differences in the kiln.  If you have temperature differentials across your kiln, any piece that crosses those boundaries will have temperature differences locked into the glass.  If you know you have temperature differentials and your glass by circumstance must be in both the cooler and the hotter regions, you need to do a standard length of soak only.  Then reduce the rate of cooling a little more than normal, so that a slower cool occurs.  This should avoid most of the stress that can be induced by very long soaks in a kiln with hot and cool spots.

The other factor against annealing too long has been revealed by Bullseye research on annealing.  This video at about 13:00 minutes into the film explains.  This complicating factor in annealing is about the difference in temperatures of the surfaces of the glass.  The research shows that the longer you anneal the greater the differential in temperature becomes between the upper and lower surfaces of the glass.  This means that you can introduce stress across the whole piece, rather than just a section as in an unevenly heated kiln.

This comes from the recording of a typical long annealing cool during my testing.

What is more, the longer you soak, the cooler the bottom becomes in relation to the top.  The reported research does not state the reasons for this.  It just commented this as an observational fact.  It can be assumed that the air temperature differences are the cause.  Even during cooling the air is hotter on top of the shelf than under.  This would allow the bottom surface to cool more than the top. This assumption is borne out by the fact that the effect is reduced or eliminated by having elements under the shelf.

There are two reasons to avoid long soaks. Uneven temperatures across the surface are locked into the glass.  And long soaks at annealing induce an unwanted temperature differential between the top and the bottom of the piece.

More information is available in the ebook Low Temperature Kilnforming; an evidence based approach to scheduling.

Crazing

Crazing appears as the multiple cracks similar to what is seen on ceramic glazes.  These occur when there is a great deal of incompatibility between the glaze and the clay body.  This can also be seen in glass.

Crazing as seen on a ceramic object

I have see crazing of glass in two circumstances.  It happens with severe devitrification, to a maximum extent of crumbling under light pressure.  This usually happens with glass not formulated for fusing, and especially on opalescent glass.

The more common occurrence is where the glass has stuck to the supporting structure.  This is frequently the case where the separator has not been sufficient to keep the glass from sticking to the shelf.  This will happen on kiln washed shelves when the coating of the separator has not been even, leaving areas with bare or very thin areas.

The standard of mixing kiln wash in the ratio of 1:5 parts by volume of powder to water is important.  The application should be with a wide soft brush such as a hake brush.  The kiln wash should be painted on in four coats, one in each direction of up, down, and the two diagonals.  A well coated shelf should have an even appearance of the coating.  Only an even film of separator is required to keep the glass from sticking to the shelf, mould or other kiln furniture.

Adjusting Cut Running Pliers

Typical cut running pliers

Cut running pliers are very useful tools if used correctly.  The pliers must have the curve in a “frown” rather than a “smile” to operate properly.  The knurled screw at the top and the scored line on the top jaw help place the pliers the right way up. They must be placed directly in line with the score. They should be only a centimetre or so onto the glass.  Holding them at the end of the handles, apply gently increasing pressure until you hear a click or see the score running.  If it does not run completely, turn the glass around and apply the pliers to the other end of the score.

Use of the Adjustment Screw

It is important to make use of the adjustment screw to get the best from the pliers.  If this is not adjusted properly, it is possible to crush the glass, or at the other extreme, not run the score at all.

The jaws need to be adjusted for the thickness of the glass.  The method I use for this is to place the edge of the runners on a corner of the glass to be scored.  

Loosen the screw until the glass is gripped by the jaws.  

Gradually tighten the screw until it resists your gentle pressure on the handles.  This gives you the correct opening of the jaws for that piece of glass.

When the pliers are properly adjusted to the thickness of the glass, you will not crush the glass and it is easy to use the pliers without cushions.

Containing Stress

People frequently report success in combining incompatible glass pieces with a larger, different base.

Questions arise.

Have the resulting pieces been tested for evidence of stress with polarised light filters?

Other destructive methods such as hot water, or placing in the freezer are not adequate measures of the long-term effects of incompatibility stress.  When you are doing something outside the accepted norms, then you must test for stress to be certain what you are producing remains sound before announcing success.

Why does glass with incompatible pieces survive?

Incompatible glass will show some stress when viewed through polarised filters. You will need to decide when it is excessive.  When viewed between polarised light filters high stress will be shown by a rainbow effect in the halo of light.  Lesser stress will be shown by pale light. The degree of stress will be shown by the amount of light.

Survivability

There are some circumstances where the glass can contain the stress, and others where it cannot.

Generally, large mass pieces can contain the stress from small incompatible pieces of glass. 

Spherical objects can contain a lot of stress over a long period, which is why glass blowers and lamp workers are generally less concerned about incompatibility than kilnformers are.

Flat glass pieces behave a little differently.

Circular forms can contain stress more easily than other shapes.  Rectangular  shapes generally show the most stress at the corners.  Narrow or wedge-shaped pieces have the most difficulty in containing stress.  The stress is concentrated at the points.

The placing of the incompatible glass is also important to the survivability of the glass.  The further from the edge of the piece, the less likely there will be breaks. 

The smaller the pieces of incompatible glass in relation to the whole, the less risk of breaking. 

The more spread apart the pieces are, the greater the chances of survival for a while or long term.

The most essential piece of equipment for people starting out and those who are investigating new setups or working at the edges of accepted norms is a pair of light polarising filters to test for stress.

When combining incompatible glasses the general case is that the greater the mass of the whole object in relation to the incompatible glass, the greater the chance of survival. 

Rakes for Combing

It is of course, possible to buy commercial tools for combing hot glass.  But with a little ingenuity, you can make your own for a small amount of money and some effort.

My raking tool is a metre long round stainless steel rod, 8mm in diameter. I sharpened it on a  grinder for metal rather than my glass grinder. Then I bent a right angle to give me 75mm "hook". The handle is a piece of broom handle. I drilled an 8mm hole in the wood and hammered it on.

A longer metal and shorter wooden handle works better than the one I made with a long wooden handle, as there is no wood near enough the heat to burn. If you do have a long handle,  soak it in water to keep it from burning.

It is possible to make a rake using mild steel rod, but it is more likely to spall and drop flakes into the glass.  Both metals need to be kept cool.  Rest the rake in a bucket of water before the first pass at combing.  As the glass stiffens and you need to wait for the glass to come back to a combing temperature, put he rake back into water to cool it.  If you try to comb with a hot rake, it will stick to the glass.

It is important to have a handle made of an insulating material to avoid any possible electrical shocks.  It also makes for a more comfortable handle that does not heat up.

Safety gear is required to protect eyes and clothing from the heat.  It is not possible to have the kiln open at around 900C without it.  This is the face, hand and arm protection I use.  The coated visor protects your eyes against the infrared radiation from the kiln.  The gloves can be the aluminised silver colour ones or the kevlar ones.  The alminised ones are easier to manipulate things with.  The arm protectors are aluminised too. They are easy to put on and give additional safety to the body.

Natural fibres should be worn to avoid clothing bursting into fire.  I use a denim jacket reversed for additional chest protection.

Fibre Paper and Fibre Blanket

Refractory fibre is generally divided into paper and blanket.  There is a distinction between the two relating to binders and thickness.

Papers are those which have binders to keep the pressed fibres in a sheet or roll.  These binders burn off during the firing process

Blanket does not have binders and is much thicker.

These two forms of refractory fibre generally exhibit a difference in thickness.  

Papers range from cartridge paper thickness, to around 6mm thick.  

Blanket tends to be 25mm and thicker, although there is some 12mm I understand.

Drying Kiln Washed Moulds

There seems to be a popular notion that newly kiln washed moulds must be cured before use.  I'm not sure where the information comes from, and no reasoning is given.  It is suggested that that quickly heating newly kiln washed moulds to 550°F (290°C) is important.

If you want to make sure the mould is dry, this may not be the best way to do it.  All ceramics have a quartz inversion at around 225°C.  This a very rapid increase in volume of 2.5% that often leads to cracks and breaks in ceramics when the rate of advance is quick.  The mould will react better and last longer if the rate of advance is slow until that inversion temperature is passed.

This is a reason to advance the temperature slowly when slumping or draping with a ceramic mould.  Another reason to heat slowly is to avoid steam formation within the ceramic body.  If the steam is created over a short time, the force can be great enough to break the ceramic.  To ensure the water evaporates, a soak at 95°C for a significant amount of time is a better, safer option.

But in addition to all these precautions, it simply is not necessary to cure kiln wash on slumping and draping moulds made of ceramics.  The glass does not begin to move until after 540°C (about 1000°F). Therefore, the kiln wash will be dry long before the glass gets near slumping temperatures.  Any vapor caused by evaporating water will escape through the vent holes in the mould or under the glass at the rim, as it will not form a seal until higher temperatures.

newly kiln washed mould beside others already fired

If you want to be sure your kiln wash is dry before you put the mould in the kiln, you can leave it in a warm ventilated space, or even on top of your kiln while it is being fired.  Using either drying method will dry the kiln wash sufficiently before the glass is placed on the slumping mould.

Kiln drying ceramic slumping and draping moulds is not necessary. It only adds another, unnecessary, step in kiln forming.  There are exceptionally good reasons to avoid rapid firing of damp moulds. The exceptions can occur with texture moulds and those intended for casting that do not have vents.

Oxidisation of Foil

Often, life intervenes between foiling and soldering.  This frequently results in the foil not accepting the solder very well, because of the mild tarnish that has occurred in the meantime.

It is a good idea to clean the foil of any possible corrosion before soldering when there has been an interval between the two processes. It is enough to clean foil with a mild abrasive such as a foam-backed scrubber from the dish washing, or fine steel wool.  I prefer the scrubber as it does not introduce another metal.  

Some people prefer a vinegar and salt solution to apply to the tarnished foil.  I am concerned about the introduction of an acid into the process causing further problems later.  I don't recommend this method of cleaning.

I then coat the exposed foil with a film of paste flux to protect from further tarnish. This acts better than any loose covering of cloth or plastic to protect from oxidation.  The purpose of flux is to both provide a "wetting" agent for the foil to accept the solder,  and to prevent oxidisation. Liquid flux cannot provide protection, once dry,  from the copper tarnishing.  I prefer the use of paste flux to reduce boiling of flux and to keep the copper free from corrosion.  The paste flux will not indefinitely prevent oxidisation, but will do so for a week or two.

Pin holes in melts

Pin holes in screen and pot melts are the result of very small bubbles rising to the surface.  These bubbles are sometimes within the glass melted, but more often come from small amounts of air trapped within the flowing glass.  These are perceived to be unsightly, or make it impractical to make a functional piece from the melt.

There are ways to minimise bubble formation or to deal with the formed bubbles.

Bubble Formation

In pot and screen melts, the glass spirals as it touches down onto the shelf. This spiralling action can trap small amounts of air as each successive spiral forms beside the previous one. Efforts at prevention of tiny bubbles in the final piece need to concentrate on this fact.

Bubble Squeeze

A preliminary element in bubble prevention is to have a long bubble squeeze to allow the glass to settle in the pot or on the screen so that the rest of the process can proceed with a minimum amount of air trapped within the flowing glass.

Two-Stage Drop

In some cases. it is possible to have the glass flow from the pot onto an angled shelf where the spiralling glass has to flow from the initial touch down to the edge and then flow onto the shelf.  This allows any tiny bubbles initially trapped to escape before the final drop onto the shelf.  This provides two mixing processes and means that a lot of clear glass needs to be included to avoid a complete mix of the colours.  It requires careful selection of the original colours to avoid a brown or black result.  It also requires a big kiln with sufficient height for a two stage drop.

This two-stage drop is of course, not suitable for a screen melt where you wish the glass strands to remain.  Nor is it suitable when you wish to have many “pools” of colour mix in the final piece.

Where the two-stage drop is not practical or suitable other methods can be used.  These relate to scheduling, cold working the surface and re-firing the piece.

Schedules

Scheduling relates to using a soak at full fuse temperature before proceeding to the anneal.  The melt will occur at 850°C to 950°C.  You can cool as fast as possible to a full fuse temperature of about 810°C and soak there for an hour or more.  This allows the small bubbles to surface, break and heal.  Schedule the rapid cool to the annealing soak, once the high temperature soak is complete.  This will eliminate lots of the bubbles, but not all.

A sample friring schedule from bubble squeeze upwards and then down to a high temperature bubble reduction soak

Cold Work

Cold working the melt is about abrading the surface to open the bubbles that are just emerging to form a small dome at the surface.  Sand blasting is a common form, as usually kiln wash or fibre needs to be removed from the bottom of the melt, and some devitrification from the surface.  It would be possible to continue to grind the surface of the glass to eliminate the small depression in the glass caused by the now opened bubble, but this is likely to expose more bubbles that were at a slightly deeper level. What next?

Fire Polish

As you will need to do a fire polish firing after blasting or grinding the surface, you can use a full fuse temperature to allow the surface to become plastic enough to fill the bubble holes.  Remember to schedule the firing as though the piece were at least 12mm thick.  You may find that more bubbles are exposed in addition to the ones healed at the conclusion of this second firing.

Flip and Fire

An alternative is to fire upside down.  You will have noted that there are no bubbles on the bottom of the melt.  This is because the bubbles have risen through the heated glass.  This physical fact can be used in the second firing.  Fire with the melt surface to the shelf.  It is best to have a clean and newly kiln washed shelf, or fibre paper (not Thinfire or Papyros) under the glass. Fire the glass to a full fuse or high temperature tack fuse with a significant length of soak to allow the bubbles near the original surface to move toward the interior of the glass.  After firing, the glass will need thorough cleaning before being fire polished. This should leave you with a pin hole free piece.

Conclusion

Achieving a pin hole free pot or screen melt requires several stages of coldworking and firing.  This makes melts inexpensive in materials (it is scrap of course) but expensive in time and firings.

Strong Frames for Stained Glass Panels

Metals

Zinc is a popular material for framing copper foiled or leaded glass panels.  It is stronger than lead – up to eight times.  It gives a feeling solidity to the edges of the panel. 

However, it does have some disadvantages.  It is difficult to patina evenly and obtain the same colour as patinaed solder.  It resistance to progressive corrosion is weaker than lead. It requires special tools to fit around curves, making it best for rectangular panels.  It does need a saw to cut evenly, but so do a lot of the stronger metals.  A look at other options is worthwhile.

The strongest option is stainless steel.  This is difficult to cut and has special welding requirements, so is only useful in large and high corrosion installations.

Mild steel is widely available and cheap.  In certain circumstances – mainly small, thin profiles – it can be soldered.  The most secure joining is done with welding.  This requires equipment that stained-glass workers do not usually have.  However, there are a large number of metal workers that can to the work for you.

Brass is more expensive than mild steel.  It is an alloy of copper and tin and so can be soldered with the tools we normally use.  It is about half the strength of stainless steel, but three times the strength of zinc.  The tin content leads to a better patina result than zinc.

Copper is up to twice the strength of zinc, but the price fluctuates more than zinc.  It can be soldered. It requires different patina solutions than used for solder.

Aluminium is the same strength as zinc, but requires different joining methods as aluminium welding is a specialist activity.  Still, it will work on rectangular items with screws at overlapping joints.

More information on the relative strengths of various metals is given in a post on metal strengths.

Strengthening lead came

Lead is weaker than lead but can be bent to conform to curves and indentations for irregular perimeters.  If copper wire is incorporated and attached to the foiled glass, the soldering of the lead came to the joints at the intersections of the solder lines and the coper/came combination will provide greater strength than the zinc alone. 

When wanting to strengthen the perimeter of rectangular or shaped perimeter leaded panels, you can use 10mm “H” lead came soldered as usual to the whole piece as an alternative to soldering the wire to the panel.  Run the copper wire in the open edge of the “H”.  Pull the wire tight at the bottom and sweat solder at each corner.  Run the wire to the top on each side, where you can make a loop for attaching hanging wires and sweat solder the wires there too.  Then close the two leaves of the lead with a fid until they come together forming a single straight line.  If you want, a “U” or “C” edging came can be soldred to the outer edge of the "H" came to cover the line created by folding the leaves.

This post gives more detail about the process of incorporating copper into the perimeter of a leaded panel.

Pot Melt Saucers as Dams for Melts

Preparation

Many ceramic plant pot saucers can be used as circular moulds.  Most are unglazed and will accept kiln wash easily.  Some are unglazed, but polished to such an extent they are no longer porous.  These and glazed flower pot saucers need some preparation before applying kiln wash.

Plant pot with saucer

Polished and glazed saucers require roughing to provide a key for the kiln wash solution to settle into.  This can be done with normal wood working sand papers.  You may want to wear a dust mask during this process, but not a lot of dust is created.  You could also use wet and dry sandpaper or diamond handpads with some water to reduce the dust further.

If the sanding of the surface does not allow the kiln wash to adhere to the saucer, you can heat it.  Soak it at about 125C for 15 minutes before removing it from the kiln to get the heat distributed throughout the ceramic body.  One advantage to the ceramic is that it holds the heat, because of its mass, for longer than steel.  Apply kiln wash with a brush or spray it onto the warm saucer.  As it dries, apply another layer of kiln wash.  Two or three applications should be enough to completely cover the surface.  If not, then you probably will need to heat up again before repeating the process.

Alternatives to plant pot saucers

There are alternatives to the saucer approach to getting thick circles from a pot melt.

 

Fibre paper

You can cut a circle from fibre paper and melt into that.  The advantage of fibre paper is that it requires little preparation other than cutting and fixing.  You may have only 3mm fibre paper and want a 9mm thick disc.  Simply fix the required number of layers together with the circle cut from each square.  The fixing can be as simple as sewing pins, copper wire, or high temperature wire.  Then place some kiln furniture on top of the surrounding fibre paper to keep it in place on the shelf during the melt.  This furniture can often be the supports for the melt.

Fibre board

If you find cutting multiple circles of the same size a nuisance, you can use fibre board.  Simply cut the circle from the board with a craft knife.  You will probably want to line the circle with fibre paper, as the cut edge of fibre board can be rough.  Alternatively, you can lightly sand the edge.  Wear a dust mask and do this outside, if possible, to keep the irritating fibres away from the studio. If you want a thicker melt than one layer of board can give, just add another in the same way as for fibre paper.

In both these cases, you may wish to put down a layer of 1mm fibre paper to ensure the glass does not stick to the shelf and does not require sandblasting.  

The advantage of the fibre paper or board alternative to flower pot saucers is that you do not need to kiln wash anything unless you want to. If you do not harden the fibre paper or board, it will not stick to the glass.

Vermiculite board

Another alternative is vermiculite board.  The advantage of this is that it comes in 25 and 50 mm thicknesses, so you can make the melt as thick as you like without having to add layers.  You can cut the vermiculite board with wood working tools.  Knives will not be strong enough to cut through the vermiculite board. You will need to kiln wash or line the vermiculite with fibre paper, as the board will stick to the glass without a separator.

Damless circles

Of course, if you want a circle without concern over the thickness, you can do the melt without any dams. You need to ensure that the shelf is level.  Any supports for the pot will need to be both kiln washed and far away enough that the moving glass does not touch the supports and distort the circle.  In general, one kilogramme of glass will give a 300mm circle, so your supports need to be further apart than the calculated diameter of the circle.  An undammed circle will vary from 6mm at the edge to as much as 12mm at the centre, depending on temperatures and lengths of soaks.

First Firing of your New Kiln

First Firing of your New Kiln

I have just been reviewing information on kiln elements. I have discovered the reason you need to do your first firing with the kiln empty of everything. No kiln wash, no kiln furniture, nothing. Vacuum the kiln to take out any dusts from travel.

The element forms a protective layer of aluminum oxide during the first firing. If there are elements of kiln wash, dusts, or glass, this will inhibit the ability of the oxide coating to be uniform. The uniform coating of the elements is important to the long life of your elements. There are other things of course, but this is the initial, essential element of preparing you kiln for use.

After this first firing you can add the other elements of kiln wash, furniture, and even glass.

In summary, fire your kiln clean and bare. No kiln wash, no furniture.

Sam Smith adds: [This] applies to kilns made with Kanthal A1 elements. Those are the good ones which last pretty much forever. Cheaper quality kilns can have nichrome elements which do not develop the coating. The firing the kiln empty allows the oxide coating to form. If you do a firing where combustion takes place such as firing fibre paper or shelf paper you should realize those combustion products are attacking your element coatings and it may be worth while venting the kiln and or firing the kiln up empty after the firing in order to protect or allow the development of a new layer of coating covering the kanthal. Kiln wash us is cheaper and safer for the long term life of your kiln elements. Smart people only purchase kilns with Kanthal elements.

Soldering Lead Came

Soldering lead came is different from soldering electronics or copper foil. For electronic soldering less heat is needed, cleanliness is all important, suitable flux is required, and the iron is held differently, among other things.

Soldering lead came The lead needs to be clean and bright to start with. If it's fairly new lead it should be solder-able without more than a scrubbing of the joints with a brass wire brush. However, if the lead is dull and oxidized, you should scrape the lead in the area to be soldered with a nail, the blade of a lead knife or other sharp edged tool until the bright metal is revealed.

an example of paste flux

Example of a tallow stick.  It has the appearance of a candle, but without the wick.

Example of the application of tallow to a joint

Then the flux can be applied.  Paste flux or tallow works best as neither flows in its cold state.  This means that you can flux the whole panel at one time without the liquid flowing away or drying.  Once the whole panel is fluxed, you do not need to stop during the soldering process.

Example of a gas powered soldering iron. The flat face of the soldering bolt is held in full contact with the joint.

An electric soldering iron is held over-handed (as you would a bread knife) in order to get the handle low enough to have the tip flat on the lead. This will be a 15 to 20 degree elevation from the horizontal. Allow the weight of the soldering iron to do the work for you. 

Let it rest on the joint after you apply the solder between the lead and the iron. In order to heat both pieces of lead you may have to rock the tip slightly to contact all leads being soldered. Take the solder away from the iron so it doesn't become attached to the joint. As soon as the solder spreads, lift the iron straight up. This process will take only a few seconds, much less than 5.

Example of smooth flat solder joints.

Avoid "painting" or dragging the iron across the joint. The object is to have a shiny, smooth, slightly rounded solder joint. Moving the iron and solder around does two things.  It makes for a weak joint as the solder does not have the chance to become stable and so forms a "pasty" joint.  Moving the iron around during the soldering of the joint often provides sharp points where the iron was moved quickly off the join. There should be no points sticking up from the solder joint. If a solder joint is not satisfactory you can re-flux and re-heat. Don't apply too much solder. It's easier to add more solder than to remove excess.