A variety of tools can be used to move frit and powders about to get the shape and edges you want.
One simple tool is a brush. It seems that a soft water colour brush is suitable for very delicate manoeuvring. There are various shapes and sizes for more and less delicate shaping. A stiffer hogs hair brush will move greater volumes.
You can also use a brush to pick up stray pieces of frit. Get the brush damp and touch it to the grains of frit to pick them up. If you do not have excess water on the brush, you will leave no mark behind.
Colour shapers with shaped, rubber tips are good for stroking and pushing frit and powder into place. There are a variety of tip shapes for various uses. Wooden tools as used for shaping clay can be useful in the same way, although they are not flexible.
Another tool that can be used is an adapted keyboard vacuum.
Monday, 21 March 2011
Thursday, 17 March 2011
Stencils for Powder Sifting
Use stiff card for the stencil. Make two little holders by sticking tape together in the middle and use the wings to attach it to the card. This makes it easy to lift the stencil straight up from the piece. Do not stick the stencil to the glass. Make the stencil with only enough surrounding card to keep the whole stiff, but ensure you can pick it up easily.
If you want to use multiple stencils on the same piece you need to ensure the stencils are all of the same size to ensure you do not mark the already laid down powder or frit. You also need to make some kind of registration mark on each stencil. Registration marks are used to align subsequent stencils in the same orientation as the first. You can use notches in the stencils and always orient them to 12 o’clock or toward some other indicator. You can also use the notch in combination with a small ink mark on the glass for accurate registration.
If you want to use multiple stencils on the same piece you need to ensure the stencils are all of the same size to ensure you do not mark the already laid down powder or frit. You also need to make some kind of registration mark on each stencil. Registration marks are used to align subsequent stencils in the same orientation as the first. You can use notches in the stencils and always orient them to 12 o’clock or toward some other indicator. You can also use the notch in combination with a small ink mark on the glass for accurate registration.
Sunday, 13 March 2011
Placing Clear on the Top
One effect of placing clear under a coloured glass, especially a dark one, is that the bubbles rising will thin the colour, even to the extent of giving a small clear circle in the midst of the colour. Placing clear on top almost completely eliminates this effect.
An additional effect of placing clear over colour, especially opals, is that it reduces devitrification.
An additional effect of placing clear over colour, especially opals, is that it reduces devitrification.
Wednesday, 9 March 2011
Glass Transition Point
This is the temperature range at which a super cooled liquid becomes a glass. At higher temperatures the molecules are able to reorganise quickly as in a liquid. At temperatures below the transition range, the movement among the molecules virtually ceases and the resulting material is known as a glass.
Two characteristics should be noted here. The temperature range for the transition phase is dependent on the speed of cooling. The slower the cooling, the more time there is for reorganisation and so there is a lower transition temperature. The quicker the cooling of the material through the transition phase, the greater the volume of the material, i.e. it is less dense, although the more slowly cooled glass is still much less dense than the crystalline material.
Based on MIT Solid State Chemistry Notes, 7, pp.7
Two characteristics should be noted here. The temperature range for the transition phase is dependent on the speed of cooling. The slower the cooling, the more time there is for reorganisation and so there is a lower transition temperature. The quicker the cooling of the material through the transition phase, the greater the volume of the material, i.e. it is less dense, although the more slowly cooled glass is still much less dense than the crystalline material.
Based on MIT Solid State Chemistry Notes, 7, pp.7
Saturday, 5 March 2011
Formation of Glass
There are a lot of glasses – natural and laboratory created – in addition to the silica based one that we work with. However understanding how glasses in general are created helps to understand “our own”. In general, when the liquid phase of a material is cooled below its freezing temperature it usually transforms into a crystalline solid. But some materials do not crystallise when cooled to their freezing temperatures. Instead they create a rigid network which is known as glass. It is very similar in structure to a liquid – hence super cooled liquid.
At temperatures just above their freezing points, most materials have viscosities that are similar to water at room temperature. They are so fluid that the molecules can rapidly form crystalline structures. But many inorganic silica materials form glasses on cooling because their viscosity at and above their freezing points is very high. There are also high energy bonds between the silicon and oxygen molecules. The viscosity increases very rapidly as the temperature is reduced. These prevent the flow required for crystallisation. In organic glasses, e.g. resin, crystallisation is difficult because of the long chain molecules that the material is composed of, preventing the molecules from sliding past one another, i.e., the difficult structural re-arrangement that would be required to form crystals.
Based on MIT Solid State Chemistry Notes, 7, pp.5-6
At temperatures just above their freezing points, most materials have viscosities that are similar to water at room temperature. They are so fluid that the molecules can rapidly form crystalline structures. But many inorganic silica materials form glasses on cooling because their viscosity at and above their freezing points is very high. There are also high energy bonds between the silicon and oxygen molecules. The viscosity increases very rapidly as the temperature is reduced. These prevent the flow required for crystallisation. In organic glasses, e.g. resin, crystallisation is difficult because of the long chain molecules that the material is composed of, preventing the molecules from sliding past one another, i.e., the difficult structural re-arrangement that would be required to form crystals.
Based on MIT Solid State Chemistry Notes, 7, pp.5-6
Tuesday, 1 March 2011
Reinforcing Panel Lamp Shades
When constructing large or heavy lamp shades, reinforcement needs to be an integral consideration in the construction. With panel lamps the reinforcement is relatively simple – it can be along the seam lines. In fact, if you do not bevel your panel edges, it can be in the upper seam lines, as the solder filling the open joint will cover the wire. If the panels are bevelled, the wire can just go on the inside along the joint.
The wire should end at the edge of the bottom of the skirt so that it does not extend beyond, but will still be in contact with the edge reinforcement. The upper wire should extend beyond the top of the shade, so that it can be soldered to the vase cap. If there is not one, the wire should be dealt with as for the bottom, and there should be edge reinforcing.
The wire that is easiest to use is single strand copper or brass. It should be of a size to fit at the bottom of the “V” of each joining panel.
Also look at the ways of reinforcing the bottom edges of lamp shades
The wire should end at the edge of the bottom of the skirt so that it does not extend beyond, but will still be in contact with the edge reinforcement. The upper wire should extend beyond the top of the shade, so that it can be soldered to the vase cap. If there is not one, the wire should be dealt with as for the bottom, and there should be edge reinforcing.
The wire that is easiest to use is single strand copper or brass. It should be of a size to fit at the bottom of the “V” of each joining panel.
Also look at the ways of reinforcing the bottom edges of lamp shades
Thursday, 17 February 2011
Flat Bottoms for Bowls
There are at least three ways to achieve flat bottoms to bowls without the use of external supports.
Using drop out rings will enable you to get a flat bottom of whatever diameter you wish depending on how long you let the aperture drop run.
You can put some dry kiln wash into the bottom of the mould, then firmly press it flat with a round piece of glass. You will need to make sure it is horizontal, so the use of a small round levelling bubble can make this easier.
Grind a flat spot on the bottom of the otherwise finished bowl. It is a good idea to use a two way leveling bubble while grinding. The round bubble is easier to use, while the two way bubbles – two leveling bubbles placed at right angles – are more accurate.
Using drop out rings will enable you to get a flat bottom of whatever diameter you wish depending on how long you let the aperture drop run.
You can put some dry kiln wash into the bottom of the mould, then firmly press it flat with a round piece of glass. You will need to make sure it is horizontal, so the use of a small round levelling bubble can make this easier.
Grind a flat spot on the bottom of the otherwise finished bowl. It is a good idea to use a two way leveling bubble while grinding. The round bubble is easier to use, while the two way bubbles – two leveling bubbles placed at right angles – are more accurate.
Sunday, 13 February 2011
Getting Water to the Mini Work Surface of a Glastar G8
Sometimes the water does not rise to the mini work surface. There are a number of things to check. These, in order, are usually the reasons the water does not get to the Mini Work Surface.
• Ensure there is enough water in reservoir, right up to the overflow
• Ensure channel from impeller to the up tube is clear
• Ensure the up tube is clear
• Ensure tap at the top is clear
• Flush the feed lines with a syringe or bulb instrument
• look at the position of the impeller on the shaft. It can move up or down. Repositioning it can improve the flow of water to the top story.
• Ensure there is enough water in reservoir, right up to the overflow
• Ensure channel from impeller to the up tube is clear
• Ensure the up tube is clear
• Ensure tap at the top is clear
• Flush the feed lines with a syringe or bulb instrument
• look at the position of the impeller on the shaft. It can move up or down. Repositioning it can improve the flow of water to the top story.
Wednesday, 9 February 2011
Supports for round bottomed bowls
A number of useful moulds for slumping do not have flat bottoms. There are a number of possibilities to have the bowl sit firmly without grinding the bottom flat. Remember that you do not need to surround the whole bottom to give the bowl stability.
Some of these include things like:
• A rubber “O” ring, although they usually come in black only.
• Thin slices of wide-diameter tubing.
• Wok support rings.
• Plastic tubing with a small joining dowel allows you to make any size. You can then paint it with the appropriate colour.
• Macramé, embroidery and curtain rings can be suitable.
• You can make them using hole saws. Cut out the big ring first so you can use the pilot hole to line up the smaller hole. Then bevel the inside to fit the bowl.
• Use three bumpons on the bottom. Be sure that the bottom of the bowl is perfectly clean, dry and free from oils. Then use some weight pressing on the bumpons for a day or more so that they stick permanently. You can do this by turning the bowl upright and fill it with some heavy objects.
Some of these include things like:
• A rubber “O” ring, although they usually come in black only.
• Thin slices of wide-diameter tubing.
• Wok support rings.
• Plastic tubing with a small joining dowel allows you to make any size. You can then paint it with the appropriate colour.
• Macramé, embroidery and curtain rings can be suitable.
• You can make them using hole saws. Cut out the big ring first so you can use the pilot hole to line up the smaller hole. Then bevel the inside to fit the bowl.
• Use three bumpons on the bottom. Be sure that the bottom of the bowl is perfectly clean, dry and free from oils. Then use some weight pressing on the bumpons for a day or more so that they stick permanently. You can do this by turning the bowl upright and fill it with some heavy objects.
Tuesday, 1 February 2011
Firing schedules – what are they for?
Firing schedules or programs are the means of controlling the temperature rises, soaks and falls to accommodate the needs of the glass. They consist of a number of segments –or steps - each of which includes: rate of temperature rise, target temperature, and soak time. They vary according to the thickness of the glass and the forming and annealing needs of the glass. Read and understand the Bullseye Technical Note on the way glass behaves at different temperatures. This will give you a good understanding of what happens to the glass at the different temperature ranges and will help you design a suitable schedule for what you want to achieve.
To assist in visualising what the numbers in a kiln programmer do, you can graph the temperature changes indicated by the numbers in the controller. Visualised from the start of the schedule, it appears as a mountain with a steep cliff on the left rising to a ledge. There is then a steeper rise to the top where there is a small plateau. The mountain then has a very steep face on the right, falling to a broad ledge a bit lower than the one on the left. There is a long shallow slope to the right of the ledge that leads to a much steeper drop to the level again. This is the shape – with variations - that you are attempting to achieve in each program/schedule.
The variations have to do with the type of glass being used and thickness of the glass. These variations determine the amount of heat and the speed with which it is put into the glass. It sets the points at which any soaks are introduced to allow the glass and associated moulds or kiln furniture to equalise in heat or to allow air to ease from between sheets of glass. It sets the top temperature and determines the length of soak at that temperature. It controls the temperature fall to the annealing soak - to equalize the temperature throughout the glass. It then controls the rate of fall to anneal the glass – removing the stress and follows up with the fall to room temperature.
A description of each of these stages includes the heat rises and any soaks required, the temperature fall, annealing soak and cool, and the cool to room temperature.
Initial heating rise
In the simplest form, the initial heating is a relatively slow rise to a point about 50C above the annealing point. This allows the glass to gain heat without thermal shock. The initial heating may be achieved in several segments, depending on what you are doing. A thick piece, or one fired many times, might be taken up in a number of stages - initially very slowly (with or without soaks - also known as holds), and then at more rapid increases. A 6mm piece being slumped into a simple curve mould would need only one segment to the top temperature.
Another example of variations required would be a 6mm piece suspended over a cylindrical mould for a drape. My experience has shown that there is a requirement for multiple segments. This starts with an initial rise of 50C/hr to 100C with a 10min soak, then 100C/hr to 250C, 10 mins, then 150C/hr to 500C, with 10mins and finally 200C/hr to forming temperature - in the region of 630C - 677C with an appropriate soak to achieve the effect desired - peeking is required to determine the length of this soak. The point being that some circumstances require much more complicated arrangements. Here it is because the mould drains the heat away from the centre of the glass while the edges heat up.
Final heating rise
Above the annealing plus 50C temperature is when the rise can be much faster up to the working/top temperature. This speed should not be as fast as possible, because it has a number of drawbacks. The speed of this rise is influenced by the amount of heat work you wish to put into the glass. This in turn will influence the top temperature and length of soak at that point.
You most often want to insert a bubble squeeze in this rise to avoid large bubbles due to trapped air.
Cooling phases
The cooling phases are several: fast drop to annealing soak, annealing cool, cool to room temperature.
Fast drop
Once the soak at top temperature is finished the requirement is to cool the glass and kiln as fast as the kiln will allow. This is to avoid the devitrification that can occur in the range of 650C to 760C.
Annealing soak
This soak at the annealing point is to allow the glass to reach the same temperature throughout from side to side and top to bottom. The length of this soak will depend on the thickness of the glass. More information on annealing is here.
Annealing phase
The slow steady cool from the annealing point to about 55C below the annealing point is where the annealing of the glass is done. What is required is a gradual, but steady decline in temperature to allow the glass to reduce in temperature evenly throughout its thickness. This even reduction in temperature should continue to the strain point and slightly below. So this phase must not be done quickly. For a 6mm piece 80C/hour is usually adequate. More on the annealing phase is available here.
Cooling to room temperature
Cooling to room temperature should be done at an even rate, although faster than the annealing cool. Too fast a cool below the strain point can cause thermal shock and therefore breakage. Typically the cool to room temperature from the strain point can be two to three times faster than the annealing cool. It is a good idea to control this cool to at least 100C. If your kiln cools more slowly than this, it will not be using any electricity, but it does protect against too rapid cooling if you open the lid or door.
To assist in visualising what the numbers in a kiln programmer do, you can graph the temperature changes indicated by the numbers in the controller. Visualised from the start of the schedule, it appears as a mountain with a steep cliff on the left rising to a ledge. There is then a steeper rise to the top where there is a small plateau. The mountain then has a very steep face on the right, falling to a broad ledge a bit lower than the one on the left. There is a long shallow slope to the right of the ledge that leads to a much steeper drop to the level again. This is the shape – with variations - that you are attempting to achieve in each program/schedule.
The variations have to do with the type of glass being used and thickness of the glass. These variations determine the amount of heat and the speed with which it is put into the glass. It sets the points at which any soaks are introduced to allow the glass and associated moulds or kiln furniture to equalise in heat or to allow air to ease from between sheets of glass. It sets the top temperature and determines the length of soak at that temperature. It controls the temperature fall to the annealing soak - to equalize the temperature throughout the glass. It then controls the rate of fall to anneal the glass – removing the stress and follows up with the fall to room temperature.
A description of each of these stages includes the heat rises and any soaks required, the temperature fall, annealing soak and cool, and the cool to room temperature.
Initial heating rise
In the simplest form, the initial heating is a relatively slow rise to a point about 50C above the annealing point. This allows the glass to gain heat without thermal shock. The initial heating may be achieved in several segments, depending on what you are doing. A thick piece, or one fired many times, might be taken up in a number of stages - initially very slowly (with or without soaks - also known as holds), and then at more rapid increases. A 6mm piece being slumped into a simple curve mould would need only one segment to the top temperature.
Another example of variations required would be a 6mm piece suspended over a cylindrical mould for a drape. My experience has shown that there is a requirement for multiple segments. This starts with an initial rise of 50C/hr to 100C with a 10min soak, then 100C/hr to 250C, 10 mins, then 150C/hr to 500C, with 10mins and finally 200C/hr to forming temperature - in the region of 630C - 677C with an appropriate soak to achieve the effect desired - peeking is required to determine the length of this soak. The point being that some circumstances require much more complicated arrangements. Here it is because the mould drains the heat away from the centre of the glass while the edges heat up.
Final heating rise
Above the annealing plus 50C temperature is when the rise can be much faster up to the working/top temperature. This speed should not be as fast as possible, because it has a number of drawbacks. The speed of this rise is influenced by the amount of heat work you wish to put into the glass. This in turn will influence the top temperature and length of soak at that point.
You most often want to insert a bubble squeeze in this rise to avoid large bubbles due to trapped air.
Cooling phases
The cooling phases are several: fast drop to annealing soak, annealing cool, cool to room temperature.
Fast drop
Once the soak at top temperature is finished the requirement is to cool the glass and kiln as fast as the kiln will allow. This is to avoid the devitrification that can occur in the range of 650C to 760C.
Annealing soak
This soak at the annealing point is to allow the glass to reach the same temperature throughout from side to side and top to bottom. The length of this soak will depend on the thickness of the glass. More information on annealing is here.
Annealing phase
The slow steady cool from the annealing point to about 55C below the annealing point is where the annealing of the glass is done. What is required is a gradual, but steady decline in temperature to allow the glass to reduce in temperature evenly throughout its thickness. This even reduction in temperature should continue to the strain point and slightly below. So this phase must not be done quickly. For a 6mm piece 80C/hour is usually adequate. More on the annealing phase is available here.
Cooling to room temperature
Cooling to room temperature should be done at an even rate, although faster than the annealing cool. Too fast a cool below the strain point can cause thermal shock and therefore breakage. Typically the cool to room temperature from the strain point can be two to three times faster than the annealing cool. It is a good idea to control this cool to at least 100C. If your kiln cools more slowly than this, it will not be using any electricity, but it does protect against too rapid cooling if you open the lid or door.
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