Placing moulds directly on shelves can cause breakage as my kiln keeps reminding me. If you put a mould directly onto the shelf, it apparently keeps the kiln from evenly heating the shelf on the way up and the mould keeps the shelf hotter than the edges on the way down. I don't know whether the shelf breaks on the way up -although I think that is so - or the way down. It doesn't happen every time, and that's why I forget.
It seems there is a critical relationship between the size of the shelf and the size of the piece covering the mould. The greater the proportion -up to some maximum, maybe 90% - the greater the likelihood of breakage it seems. A fully covered shelf would heat and cool along with the mould. When the mould is small in relation to the shelf, the heat can travel under the mould well enough to avoid breaking, it appears. It is the large range in between that causes the trouble.
A preventative is to fire without a shelf. But failing that possibility, raise the mould a little from the shelf with kiln furniture or pieces of thick fibre paper. Also keep the shelf elevated a little from the floor of the kiln.
Saturday, 8 May 2010
Tuesday, 4 May 2010
Grinding to Shape
There are lots of ways people use to keep marks on the glass while grinding.
Paint markers will stand up to a lot of water if allowed to dry before being taken to the grinder.
Covering the marker line with Vaseline or lip salve will preserve the line longer.
Sticking down a water proof pattern piece on the glass will allow grinding up to the edges of the pattern piece without it breaking down. But of course, it can be ground away or pushed aside by the grinding head.
All these methods assume that there is a lot of grinding needed.
If you cut accurately, only a small amount of grinding will be needed and permanent felt tip/marker on glass lasts long enough to do the job.
Paint markers will stand up to a lot of water if allowed to dry before being taken to the grinder.
Covering the marker line with Vaseline or lip salve will preserve the line longer.
Sticking down a water proof pattern piece on the glass will allow grinding up to the edges of the pattern piece without it breaking down. But of course, it can be ground away or pushed aside by the grinding head.
All these methods assume that there is a lot of grinding needed.
If you cut accurately, only a small amount of grinding will be needed and permanent felt tip/marker on glass lasts long enough to do the job.
Friday, 30 April 2010
Rapid Heat Rises and Their Effects on Firings
Based on a communication from Phil Hoppes
A word of caution. Never use 9999 for a ramp up. Note: 9999 just means on an up ramp the elements are full on, no cycling. On the down ramp the power is completely off until the desired temperature is reached. Your kiln will rise in temperature limited by 2 things - the type of insulation and the number of elements. This can be anywhere from 300 – 450C/hr. to as high as 1600C/hr.)
If the time it takes to go from your lower temp to your upper temp is less than 40 minutes, your controller will be unable to accurately control the top temperature. For example, if you want to ramp from room temperature (20C) to 300C and for your kiln 9999 on an up ramp is 850C/hr., the temperature rise you are looking to accomplish is 280C and your kiln will reach 300C in just under 20 minutes. The problem is that most controllers need around 40 minutes in any ramp cycle to "learn" how the kiln is responding to the inputs that are given to it by the controller. Slower ramps need less “learning” time, faster ramps need more time.
What will happen if you programme a ramp shorter than your controller will respond to is that the temperature in your kiln will not stop nicely at the programmed 300C. The controller has not learned how to stop your kiln from rising in temperature yet and the temperature will rise much higher than your programmed value.
Depending on your kiln and your controller this can be quite significant. Most controllers have a peak shut off value, somewhere between 55C and 85C above your programmed amount. Some controllers allow you to program this value also. If the temperature in your kiln overshoots the value it was programmed to stop and the amount of overshoot exceeds the programmed shutoff temp your controller will shut down. This is a safety feature and the controller is doing what it is suppose to do. If you have something in your kiln however and this happens it will not be annealed properly and you will have to very carefully re-fire to remove the stress or it will break into pieces.
It is a good idea to know just what your kiln will do. You can do this by taking an empty kiln, program 9999 in an up ramp from room temp to 815C. This is the typical peak you would use in a full fuse. See how long it takes for your kiln to reach this temp. This will give you the maximum up ramp rate of your kiln. You can use this rate to calculate if you violate the “learning” margin of the controller.
It is advisable not to exceed 350C/hr up ramp unless overshooting the top temperature does not matter.
The 9999 ramp in almost all cases will be used to go from the top temperature to the start of the annealing cycle.
A word of caution. Never use 9999 for a ramp up. Note: 9999 just means on an up ramp the elements are full on, no cycling. On the down ramp the power is completely off until the desired temperature is reached. Your kiln will rise in temperature limited by 2 things - the type of insulation and the number of elements. This can be anywhere from 300 – 450C/hr. to as high as 1600C/hr.)
If the time it takes to go from your lower temp to your upper temp is less than 40 minutes, your controller will be unable to accurately control the top temperature. For example, if you want to ramp from room temperature (20C) to 300C and for your kiln 9999 on an up ramp is 850C/hr., the temperature rise you are looking to accomplish is 280C and your kiln will reach 300C in just under 20 minutes. The problem is that most controllers need around 40 minutes in any ramp cycle to "learn" how the kiln is responding to the inputs that are given to it by the controller. Slower ramps need less “learning” time, faster ramps need more time.
What will happen if you programme a ramp shorter than your controller will respond to is that the temperature in your kiln will not stop nicely at the programmed 300C. The controller has not learned how to stop your kiln from rising in temperature yet and the temperature will rise much higher than your programmed value.
Depending on your kiln and your controller this can be quite significant. Most controllers have a peak shut off value, somewhere between 55C and 85C above your programmed amount. Some controllers allow you to program this value also. If the temperature in your kiln overshoots the value it was programmed to stop and the amount of overshoot exceeds the programmed shutoff temp your controller will shut down. This is a safety feature and the controller is doing what it is suppose to do. If you have something in your kiln however and this happens it will not be annealed properly and you will have to very carefully re-fire to remove the stress or it will break into pieces.
It is a good idea to know just what your kiln will do. You can do this by taking an empty kiln, program 9999 in an up ramp from room temp to 815C. This is the typical peak you would use in a full fuse. See how long it takes for your kiln to reach this temp. This will give you the maximum up ramp rate of your kiln. You can use this rate to calculate if you violate the “learning” margin of the controller.
It is advisable not to exceed 350C/hr up ramp unless overshooting the top temperature does not matter.
The 9999 ramp in almost all cases will be used to go from the top temperature to the start of the annealing cycle.
Monday, 26 April 2010
Prevention of Needling in Dammed/ Box Cast Work
To avoid needling in box cast or dammed work you need to provide a space for the glass to flow into.
This is done by using 3mm thick fibre paper to line the damming materials. The fibre paper is cut to 3mm less than the finished height of the fired piece.
Fire the glass with a long bubble soak. This allows the glass to almost achieve its final height before it becomes less viscous. It will still be higher than the fibre paper and as the glass continues to be more “soft” it will round as it reaches full fusing temperature. There is not enough glass above the fibre – only 3mm – for the glass to run over the fibre, as the surface tension holds it in until 6 or 7mm above the fibre. The top edge of the glass does not touch the fibre or dam, so there are no needles.
Another way to avoid needles in this kind of work is to make the dams larger than the glass being contained. That is, place the dams a short distance away from the glass. The glass will then flow out to meet the dams. Since the glass is not contracting it will not have needles. This is a good solution when the thickness of the glass is not critical. You control the area of the piece by the placing of the dams.
This is done by using 3mm thick fibre paper to line the damming materials. The fibre paper is cut to 3mm less than the finished height of the fired piece.
Fire the glass with a long bubble soak. This allows the glass to almost achieve its final height before it becomes less viscous. It will still be higher than the fibre paper and as the glass continues to be more “soft” it will round as it reaches full fusing temperature. There is not enough glass above the fibre – only 3mm – for the glass to run over the fibre, as the surface tension holds it in until 6 or 7mm above the fibre. The top edge of the glass does not touch the fibre or dam, so there are no needles.
Another way to avoid needles in this kind of work is to make the dams larger than the glass being contained. That is, place the dams a short distance away from the glass. The glass will then flow out to meet the dams. Since the glass is not contracting it will not have needles. This is a good solution when the thickness of the glass is not critical. You control the area of the piece by the placing of the dams.
Saturday, 10 April 2010
Charging the Pot for a Melt
The way you charge (load the glass into) the pot makes a difference to the resulting piece.
A good way to get strong colour separation is to put two colours on opposite sides and a third colour or clear between them. The two side colours will have best separation if they are not more than 1/3 each. As the glass begins to flow out of the pot, all three colours will come out at once and form concentric circles (assuming a circular hole in the pot).
You can manipulate and alter the results with a fair amount of predictability by changing the diameter and shape of the hole, charging the pot with more than three colours or less, rearranging the orientation into a sunburst orientation or whatever comes to mind. Be sure to keep notes on what you did and what the results were in case you want to reproduce the effect.
Think about how the glass will flow out of the pot when you charge it with glass. If you layer colours horizontally from C (on top) to A (on bottom), it will initially flow out in colour A, then B, then C. After that initial flow, which will be on the outside of the finished piece, the main flow will be from the top (C), then the middle (B) and finally the bottom (A). This is because after the initial flow, the rest of the glass comes out in a funnel shape pulling the top and small portions of the underlying glass.
This means that layering is the best way of mixing colours. You need to think about colour combinations too. For example yellow and red become brown; yellow and blue a dark green, etc.
The proportion of dark colours is important, for example, as little as 2% of black can make the whole piece very dark. If you have dark colours, you need to add a large proportion of clear or very light opalescent glass.
If you use frit, large pieces are better than smaller ones. Even so, you need to be careful about the colours you use so the whole does not become muddy.
A good way to get strong colour separation is to put two colours on opposite sides and a third colour or clear between them. The two side colours will have best separation if they are not more than 1/3 each. As the glass begins to flow out of the pot, all three colours will come out at once and form concentric circles (assuming a circular hole in the pot).
 |
| Vertical stacking of multiple colours |
You can manipulate and alter the results with a fair amount of predictability by changing the diameter and shape of the hole, charging the pot with more than three colours or less, rearranging the orientation into a sunburst orientation or whatever comes to mind. Be sure to keep notes on what you did and what the results were in case you want to reproduce the effect.
Think about how the glass will flow out of the pot when you charge it with glass. If you layer colours horizontally from C (on top) to A (on bottom), it will initially flow out in colour A, then B, then C. After that initial flow, which will be on the outside of the finished piece, the main flow will be from the top (C), then the middle (B) and finally the bottom (A). This is because after the initial flow, the rest of the glass comes out in a funnel shape pulling the top and small portions of the underlying glass.
This means that layering is the best way of mixing colours. You need to think about colour combinations too. For example yellow and red become brown; yellow and blue a dark green, etc.
The proportion of dark colours is important, for example, as little as 2% of black can make the whole piece very dark. If you have dark colours, you need to add a large proportion of clear or very light opalescent glass.
If you use frit, large pieces are better than smaller ones. Even so, you need to be careful about the colours you use so the whole does not become muddy.
Tuesday, 6 April 2010
Aperture Pours
The most commonly used aperture pours are Pot melts and wire melts. Pot melts use containers, and wire mesh for wire melts. In both cases they control the way the glass melts into a container or directly on the shelf below.
The materials are stainless steel wire grids, and unglazed terracotta pots. The spacing of the steel grid will determine the number of trails of glass falling. So a finer grid will give more points of expansion in the resulting melt. But will mix the colours much more thoroughly than a coarser mesh will.
Doing a pot melt usually provides a simpler pattern of flow. A single round hole gives one circular point from which the glass expands. A single rectangular hole gives a single ribbon shape as the expansion point. You can, of course, have multiple holes in the bottom of the pot to provide a more complex interaction of the flowing glass. The wider the rim of the pot in relation to its depth, the more flexible it will be. You can put more glass in the pot and you can have it higher in the kiln.
The arrangement of glass in the pot will produce different results. There are two basic arrangements: colours layered one above each other as in a layer cake; and colours arranged on end around the sides of the pot. When loading the pot you need to remember that although the glass immediately above the hole will be the first to come out – and therefore be at the edge of the melt – the remainder of the glass comes out in a funnel-like order, with the glass at the bottom corner of the pot being the last to flow out – and become the centre of the melt.
There is a relationship between the hole size and distance to surface that affects the final appearance. The larger the hole the less likely the glass is to spiral as it falls, so you need a greater distance between the bottom of the pot and the shelf. The smaller the hole, the less distance you need. Only experience will tell you what distance and size you need or can use.
You can calculate the amount of glass for different sizes by using this table. If you have a rectangular space you are dropping into, you can calculate the volume of glass by multiplying the width, length and desired thickness – all in centimetres. This will give the volume in cubic centimetres and to convert that into weight, you multiply the volume by the specific gravity of glass - 2.5 is near enough – to get the number of grams of glass required. To convert into kilograms, divide by 1000.
By dropping directly onto kiln washed shelf, ring or circular container you will get some contamination. There are some ways to avoid this given here.
You can also use this method to act as a crucible to pour glass into closed moulds.
 |
| Emptied pot melt |
 |
| Finished screen melt |
Doing a pot melt usually provides a simpler pattern of flow. A single round hole gives one circular point from which the glass expands. A single rectangular hole gives a single ribbon shape as the expansion point. You can, of course, have multiple holes in the bottom of the pot to provide a more complex interaction of the flowing glass. The wider the rim of the pot in relation to its depth, the more flexible it will be. You can put more glass in the pot and you can have it higher in the kiln.
The arrangement of glass in the pot will produce different results. There are two basic arrangements: colours layered one above each other as in a layer cake; and colours arranged on end around the sides of the pot. When loading the pot you need to remember that although the glass immediately above the hole will be the first to come out – and therefore be at the edge of the melt – the remainder of the glass comes out in a funnel-like order, with the glass at the bottom corner of the pot being the last to flow out – and become the centre of the melt.
There is a relationship between the hole size and distance to surface that affects the final appearance. The larger the hole the less likely the glass is to spiral as it falls, so you need a greater distance between the bottom of the pot and the shelf. The smaller the hole, the less distance you need. Only experience will tell you what distance and size you need or can use.
You can calculate the amount of glass for different sizes by using this table. If you have a rectangular space you are dropping into, you can calculate the volume of glass by multiplying the width, length and desired thickness – all in centimetres. This will give the volume in cubic centimetres and to convert that into weight, you multiply the volume by the specific gravity of glass - 2.5 is near enough – to get the number of grams of glass required. To convert into kilograms, divide by 1000.
By dropping directly onto kiln washed shelf, ring or circular container you will get some contamination. There are some ways to avoid this given here.
You can also use this method to act as a crucible to pour glass into closed moulds.
Thursday, 18 March 2010
Pattern Scissors Usage
The purpose of pattern shears/scissors is to cut out the space between pattern pieces equivalent to the came heart or the space needed for foil.
The scissors come in two thicknesses – one for leaded and the thinner for copper foil.
If you must use them:Use in short cutting motions. Use only the first 50mm of the blades which are closest to the pivot point. Otherwise the paper jams in between the blades. It remains difficult to cut long straight lines without quickly having an “accordion” of paper blocking the cutting action.
Some suggestions to make things easier:
- Clean the blades regularly. If you are cutting anything with adhesives, clean the blades after each use with spirits.
- Often running a little soap along the blades helps to smooth the action of the blades.
- Use stiff high quality paper so you do not catch fibres in the scissors. Waxed paper or stencil card are good materials to use.
Organising pattern pieces.
- You have made a second and third copy of the cartoon haven’t you?
- Now that you have a lot of pieces what do you do with them?
- Mark any grain direction before you cut the pieces apart.
You need to code the pieces in some way.
- Numbering with reference to the main cartoon is most common.
- It is a good idea to colour code the pieces and if the surface will take it, a shading of the colour makes a quick visual reference.
Keeping the pieces together.
- Envelopes are easy to write on for colours, or areas such as borders, background, etc.
- Freezer bags that are transparent and have a band to write on are very good, as you can see the pieces without opening the bag.
- You need a labelled bag or container to keep all the envelopes together.
Alternatives to pattern scissors
- For copper foil, you can use normal scissors, by cutting to the inside of the pencil or inked line. - You can also use a scalpel or craft knife to cut to the insides of the marked lines.
- For leaded glass you can use a felt tip pen (a bullet point is almost exactly the right width when new). Cut with scissors or craft knife at the sides of the line.
Alternative to pattern piecesUse the European or trace cutting method as described here.
The scissors come in two thicknesses – one for leaded and the thinner for copper foil.
If you must use them:Use in short cutting motions. Use only the first 50mm of the blades which are closest to the pivot point. Otherwise the paper jams in between the blades. It remains difficult to cut long straight lines without quickly having an “accordion” of paper blocking the cutting action.
Some suggestions to make things easier:
- Clean the blades regularly. If you are cutting anything with adhesives, clean the blades after each use with spirits.
- Often running a little soap along the blades helps to smooth the action of the blades.
- Use stiff high quality paper so you do not catch fibres in the scissors. Waxed paper or stencil card are good materials to use.
Organising pattern pieces.
- You have made a second and third copy of the cartoon haven’t you?
- Now that you have a lot of pieces what do you do with them?
- Mark any grain direction before you cut the pieces apart.
You need to code the pieces in some way.
- Numbering with reference to the main cartoon is most common.
- It is a good idea to colour code the pieces and if the surface will take it, a shading of the colour makes a quick visual reference.
Keeping the pieces together.
- Envelopes are easy to write on for colours, or areas such as borders, background, etc.
- Freezer bags that are transparent and have a band to write on are very good, as you can see the pieces without opening the bag.
- You need a labelled bag or container to keep all the envelopes together.
Alternatives to pattern scissors
- For copper foil, you can use normal scissors, by cutting to the inside of the pencil or inked line. - You can also use a scalpel or craft knife to cut to the insides of the marked lines.
- For leaded glass you can use a felt tip pen (a bullet point is almost exactly the right width when new). Cut with scissors or craft knife at the sides of the line.
Alternative to pattern piecesUse the European or trace cutting method as described here.
Sunday, 14 March 2010
Removing Stick-on Lead and Film
It is possible to do this. It is a labour intensive process. You do need to be careful to avoid scratching the glass.
Cut through a lead line and carefully rip away the lead tape, being careful to not pull so hard that you flex the centre of the glass and cause it to break. You will need considerable force. The bulk of the lead is probably positioned over the film, so bulk of the the glue residue from the lead tape will come off when the film is peeled away. With a spray bottle mist the glass with white spirit and scrub using a cloth. If the glue is especially resistant use a broad wallpaper scraper and cover it with the kerosene soaked cloth to scrape the glue off. Use vinyl or latex gloves.
However, the manufacturer comments that stained glass overlay is virtually impossible to remove. It is better to replace the glass. It will save time, expense and possible tears.
Cut through a lead line and carefully rip away the lead tape, being careful to not pull so hard that you flex the centre of the glass and cause it to break. You will need considerable force. The bulk of the lead is probably positioned over the film, so bulk of the the glue residue from the lead tape will come off when the film is peeled away. With a spray bottle mist the glass with white spirit and scrub using a cloth. If the glue is especially resistant use a broad wallpaper scraper and cover it with the kerosene soaked cloth to scrape the glue off. Use vinyl or latex gloves.
However, the manufacturer comments that stained glass overlay is virtually impossible to remove. It is better to replace the glass. It will save time, expense and possible tears.
Saturday, 6 March 2010
Commissioning
Commissioning a stained glass window, screen or lamp involves entering into a contract with the designer/maker. It is therefore important that both client and maker know exactly what is involved.
· The price of the work should be established. The materials used in the making of a window, especially the glass itself, can be expensive and the possibility of commissioning a well-designed leaded light should not be ignored.
· The maker will need to know the budget for the work and will provide an estimate, and may require a down payment before beginning work and perhaps payment by instalments, depending upon the cost of the materials involved.
The designer will prepare a preliminary design, according to the client's brief.
· The design should indicate the nature of the construction and the position of any ferramenta or physical support.
· This design should be as detailed as possible. It may be accompanied by samples of the proposed glasses.
· The client must be prepared to recompense an artist for design(s) prepared according to a brief, whether or not it proceeds to execution.
· The copyright in all cases remains the property of the artist.
The arrangements for the execution of the commission must also be satisfactorily established, including those for installation. If necessary, the advice of an architect should be sought; for church commissions, the architect responsible for the church should be involved from the outset. If the window is to be sited in an exposed position or in an area where vandalism is known to be a problem, protective measures should be considered.
Also look at Commission Agreements
· The price of the work should be established. The materials used in the making of a window, especially the glass itself, can be expensive and the possibility of commissioning a well-designed leaded light should not be ignored.
· The maker will need to know the budget for the work and will provide an estimate, and may require a down payment before beginning work and perhaps payment by instalments, depending upon the cost of the materials involved.
The designer will prepare a preliminary design, according to the client's brief.
· The design should indicate the nature of the construction and the position of any ferramenta or physical support.
· This design should be as detailed as possible. It may be accompanied by samples of the proposed glasses.
· The client must be prepared to recompense an artist for design(s) prepared according to a brief, whether or not it proceeds to execution.
· The copyright in all cases remains the property of the artist.
The arrangements for the execution of the commission must also be satisfactorily established, including those for installation. If necessary, the advice of an architect should be sought; for church commissions, the architect responsible for the church should be involved from the outset. If the window is to be sited in an exposed position or in an area where vandalism is known to be a problem, protective measures should be considered.
Also look at Commission Agreements
Tuesday, 2 March 2010
Effect of Plaster-Water Ratio on Some Properties
Plaster-water ratio (by weight) 100/30
Setting time (min) 1.75
Compression strength (kg/sq.cm) 808
Dry Density (kg/cu metre) 1806
Plaster-water ratio (by weight) 100/40
Setting time (min) 3.25
Compression strength (kg/sq.cm)474
Dry Density (kg/cu metre) 1548
Plaster-water ratio (by weight) 100/50
Setting time (min) 5.25
Compression strength (kg/sq.cm)316
Dry Density (kg/cu metre) 1352
Plaster-water ratio (by weight) 100/60
Setting time (min) 7.24
Compression strength (kg/sq.cm)228
Dry Density (kg/cu metre) 1206
Plaster-water ratio (by weight) 100/70
Setting time (min) 8.25
Compression strength (kg/sq.cm)175
Dry Density (kg/cu metre) 1083
Plaster-water ratio (by weight) 100/80
Setting time (min) 10.50
Compression strength (kg/sq.cm)126
Dry Density (kg/cu metre) 990
Plaster-water ratio (by weight) 100/90
Setting time (min) 12.00
Compression strength (kg/sq.cm)98
Dry Density (kg/cu metre) 908
Plaster-water ratio (by weight) 100/100
Setting time (min) 13.75
Compression strength (kg/sq.cm) 70
Dry Density (kg/cu metre) 867
This table of relationships makes it clear that the less weight of water added to the plaster, the stronger the resulting mould will be. It also is clear that with less water, the setting time is reduced. So some compromise may be needed to be able to pour the mixture before it sets.
Setting time (min) 1.75
Compression strength (kg/sq.cm) 808
Dry Density (kg/cu metre) 1806
Plaster-water ratio (by weight) 100/40
Setting time (min) 3.25
Compression strength (kg/sq.cm)474
Dry Density (kg/cu metre) 1548
Plaster-water ratio (by weight) 100/50
Setting time (min) 5.25
Compression strength (kg/sq.cm)316
Dry Density (kg/cu metre) 1352
Plaster-water ratio (by weight) 100/60
Setting time (min) 7.24
Compression strength (kg/sq.cm)228
Dry Density (kg/cu metre) 1206
Plaster-water ratio (by weight) 100/70
Setting time (min) 8.25
Compression strength (kg/sq.cm)175
Dry Density (kg/cu metre) 1083
Plaster-water ratio (by weight) 100/80
Setting time (min) 10.50
Compression strength (kg/sq.cm)126
Dry Density (kg/cu metre) 990
Plaster-water ratio (by weight) 100/90
Setting time (min) 12.00
Compression strength (kg/sq.cm)98
Dry Density (kg/cu metre) 908
Plaster-water ratio (by weight) 100/100
Setting time (min) 13.75
Compression strength (kg/sq.cm) 70
Dry Density (kg/cu metre) 867
This table of relationships makes it clear that the less weight of water added to the plaster, the stronger the resulting mould will be. It also is clear that with less water, the setting time is reduced. So some compromise may be needed to be able to pour the mixture before it sets.
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