Damming Irregular Shapes

The assumption is that these pieces will be open-face thick fusings/castings rather than enclosed castings.

There are two basic types of dams: a shape cut from a single surrounding piece, or multiple pieces held in place.

Single piece dams

A large, thick fibre board with shape cut out will confine the glass. If very thick, you may need to weight the fibre board, as it is lighter than the glass.

Another variation is to use thick fibre paper cut out to shape and layered up to the desired height with stainless steel pins to hold the whole in place. This also may need to be weighted down. A variation on this is to place the whole on a fibre board and pin the layers of fibre paper into the fibre board to maintain the position of the fibre dams. This will not normally need weighting.



Multiple piece dams

If the shapes are not extreme, you can use pieces of fibre board or fibre paper backed up with kiln furniture, bits of broken kiln shelf or any other heavy material that will withstand the heat of fusing.

You can use thick fibre paper held in place with kiln furniture, if the piece is not thick. You do have to be careful that the glass does not float the fibre paper and run underneath, so about 10 mm is the maximum for this kind of damming. It also helps if this kind of dam is made larger than the glass – or alternatively the glass smaller than the dam. This allows the glass to flow out toward the dam, giving nice curved edges.

Moulds, stainless steel and other refractory materials can be specially made for shapes that will be repeated.

Note that all these variations will benefit from being lined with Thinfire backed up with fibre paper.  This gives a smoother edge and also gives some cusioning between the dam and the glass.

Coating Metal Moulds

Most metal moulds are stainless steel as it spalls less while at forming temperatures. The techniques here can be applied to any metal, although spalling will be a common occurrence on any metal other than high grade stainless steel.

On many single curve moulds, such as a partial cylinder, you can just lay fibre paper over the form and place the glass on top of that.

Metal moulds that have more complex shapes require a separator that will conform to those shapes. Applying liquid kiln wash requires you to heat the steel to somewhere between 150 and 200C before applying the kiln wash. Any hotter and the kiln wash will boil off on contact, leaving an uneven coating.

The kiln wash can be applied with a brush or by spraying. Spraying gives a smoother less streaky application. After giving the mould the first coat, return the mould to the kiln and re-heat the mould. Repeat this until you have covered the whole mould with a thin layer of separator. Be careful and avoid applying too much kiln wash at once, as that will cause the separator to run and reveal bare spots on the mould, causing you to need to clean and begin again.

Cleaning Glass

Glass with dust, oil or other residues promotes devitrification. So first try to remove any excess of these.

Cutting without oil can avoid introducing more oils. Specially formulated cuttings fluids are available that are not oil.

Wash with only a few drops of washing up liquid of the kind without additives to keep you hands soft, or smell good. If there are soap bubbles on top of the water, you are using too much soap.

Window cleaning products are not usually appropriate, especially if they contain ammonia. A few products do not have additives that promote devitrification. One that works well for me is the Bohle aerosol cleaner (but not the concentrate).

Be careful about your rinsing water. If it has mineral salts in it, it can form nucleation points for devit.

Polish dry using plain paper towels or microfiber cloths. Change frequently and wash without softeners.

If you are grinding the edges, clean immediately before any part dries to avoid the powdered glass filling the scratches caused by grinding. Some put the ground pieces into a bowl of water immediately to keep the edges wet until cleaning can be done.

Moving Pieces

To keep pieces from moving about as you solder them, use pins or nails to keep them in place. The best is to assemble the whole panel and then keep them in place with a frame or lots of nails/pins around the outside. This keeps pieces from moving and also keeps the panel to the original size.

The type of nail or pin will depend on the work board you are using. Softer boards allow push pins of various sorts to be used. Harder boards will need nails.

If you don’t like assembling the whole before soldering, you can confine the pieces you are currently soldering with nails/pins in the same fashion as for the whole panel.



It also helps to do a little tack soldering before the process of running a bead begins. A small amount of solder on the copper foil where pieces join will keep the pieces in exact alignment while you are running a bead.

Devitrification of Edges

Devitrification often occurs on the edges of glass, and can be seen as a thin line of devitrification -often looking like smudges that won't wipe off - where the edge has flattened during the fusing. There are some ways to avoid this.

Avoid grinding if at all possible.

If you must grind, use fine heads/grits. Then clean immediately before any part of the glass dries. You may need to clean part of the glass piece before the grinding is complete to avoid any drying of the powder on the edge of the glass.

Clean well with a minimum of soap and rinse with water that does not have a lot of minerals in it. Polish well with plain paper towels or frequently changed microfiber cloths.

Window cleaning products are not usually appropriate, especially if they contain ammonia.

Avoid introducing oils from the cutter by scoring with a dry cutter or use a specially devised cutting fluid. Cleaning solutions that have additives to be kind to hands or scents should be avoided.

The edges of some glasses devitrify more easily than others. If this continues to be the case after all cleaning efforts have failed, then use a devitrification spray, but continued cleaning is still necessary. There are no short cuts in cleaning.

Effect of Variations in Size on Bead Annealing

When annealing beads with varying thicknesses, I apply a rule of thumb to be safe.

I take the difference between the thickest and the thinnest part and add that to the thickest part to get the diameter at which I should anneal.

So a bead with a thickest part being 8mm and the thinnest 2mm, gives a difference of 6mm which I add to the 8mm (thickest) part giving 14mm as the diameter to which I anneal.

Annealing Beads of different sizes and shapes

It is possible to anneal beads of different sizes and shapes at the same time, if you anneal for the beads which require the most care. It will not matter for the smaller beads or easier shapes if they are annealed longer than the minimum requirement.

Effect of Shape on Bead Annealing

The shape of the bead has significant effects on the annealing time required. This is because the shape has an effect on the speed at which the centre can cool. Spheres have the most even transmission of heat, because the heat can radiate equally in all directions. Cylinders are more restricted in heat radiation because they can radiate heat from the circumference but not so effectively along the length. Flat shapes can radiate heat in only two directions, making them the most difficult to anneal.

As indicated, spheres can be annealed most quickly. The annealing schedules given in this blog apply to spheres as this is the most common form for beads.

Cylinders which by definition are longer than the diameter need to be annealed at two thirds the rate of spheres. So, from the tables you choose the annealing rate for a piece 1.5 times larger than the diameter of your cylinder.

Flat shapes require the most care in annealing so you should choose the rate that is three times the thickness of the piece you are annealing.

These cautions will help to adequately anneal your beads, what ever their shape.

Bead Annealing Schedules for Spectrum Beads

Bead Annealing Schedules for Spectrum Beads
This table is based on James Kirwin’s work on bead making with variations. This is for cold beads being heated for a secure anneal.

Up to 10mm dia.: afap to 520C, 30 mins; anneal at 300C/hr to 370C; afap to 40C
12mm dia.: 1000C/hr to 520C,30mins; anneal at 210C/hr; 600C/hr to 40C
14mm dia.: 1000C/hr to 520C, 30mins; anneal at 155C/hr; 460C/hr to 40C
16mm dia.: 950C/hr to 520C, 30mins; anneal at 120C/hr; 350C/hr to 40C
18mm dia.: 740C/hr to 520C, 30mins; anneal at 94C/hr; 280C/hr to 40C
20mm dia.: 600C/hr to 520C, 30mins; anneal at 75C/hr; 230C/hr to 40C
22mm dia.: 500C/hr to 520C, 30mins; anneal at 62C/hr; 185C/hr to 40C
24mm dia.: 420C/hr to 520C, 30mins; anneal at 53C/hr; 155C/hr to 40C
30mm dia.: 270C/hr to 520C, 36mins; anneal at 33C/hr; 100C/hr to 40C
38mm dia.: 165C/hr to 520C, 39mins; anneal at 21C/hr; 60C/hr to 40C
50mm dia.: 95C/hr to 520C, 46mins; anneal at 12C/hr; 36C/hr to 40C

Remember this table is for spheres. For cylinders choose the diameter that is 1.5 times the diameter of your cylinder, and for flat shapes choose the diameter that is 3 times the thickness of your piece.

For other information on annealing of beads go here

Bead Annealing Schedule for Effetre Beads

This table is based on James Kirwin’s work on bead making with variations. This is for cold beads being heated for a secure anneal.

Up to 10mm dia.: afap to 530C, 30 mins; cool at 280C/hr to 360C; 840C to 40C.
12mm dia.: Go at 1000C/hr to 530C, 30mins.; cool at 194C/hr to 360C; at 580C/hr to 40C
14mm dia.: Go at 1000C/hr to 530C, 30mins.; cool at 142C/hr to 360C; at 425C/hr to 40C
16mm dia.: Go at 870C/hr to 530C, 30mins.; cool at 109C/hr to 360C; at 330C/hr to 40C
18mm dia.: Go at 690C/hr to 530C, 30mins.; cool at 86C/hr to 360C; at 260C/hr to 40C
20mm dia.: Go at 560C/hr to 530C, 30mins.; cool at 70C/hr to 360C; at 210C/hr to 40C
22mm dia.: Go at 460C/hr to 530C, 30mins.; cool at 57C/hr to 360C; at 175C/hr to 40C
24mm dia.: Go at 390C/hr to 530C, 30mins.; cool at 48C/hr to 360C; at 145C/hr to 40C
30mm dia.: Go at 245C/hr to 530C, 36mins.; cool at 31C/hr to 360C; at 95C/hr to 40C
38mm dia.: Go at 155C/hr to 530C, 39mins.; cool at 19C/hr to 360C; at 60C/hr to 40C
50mm dia.: Go at 90C/hr to 530C, 46mins.; cool at 12C/hr to 360C; at 36C/hr to 40C


Remember this table is for spheres. For cylinders choose the diameter that is 1.5 times the diameter of your cylinder, and for flat shapes choose the diameter that is 3 times the thickness of your piece.

For other information on annealing of beads go here

Bead Annealing Schedule for Bullseye Beads

This table is based on James Kirwin’s work on bead making with variations. This is for cold beads being heated for a secure anneal.

Up to 10mm dia.: afap to 540C, soak for 30min., cool at 300C/hr to 370C; afap to 40C.
12mm dia.: 1000C/hr to 540C, soak for 30min., cool at 220C/hr to 370C; 600C/hr to 40C
14mm dia.: 1000C/hr to 540C, soak for 30min., cool at 165C/hr to 370C; 480C/hr to 40C
16mm dia.: 1000C/hr to 540C, soak for 30min., cool at 125C/hr to 370C; 375C/hr to 40C
18mm dia.: 900C/hr to 540C, soak for 30min., cool at 100C/hr to 370C; 300C/hr to 40C
20mm dia.: 600C/hr to 540C, soak for 30min., cool at 80C/hr to 370C; 240C/hr to 40C
22mm dia.: 535C/hr to 540C, soak for 30min., cool at 67C/hr to 370C; 200C/hr to 40C
24mm dia.: 450C/hr to 540C, soak for 30min., cool at 55C/hr to 370C; 165C/hr to 40C
30mm dia.: 280C/hr to 540C, soak for 36min., cool at 36C/hr to 370C; 110C/hr to 40C
38mm dia.: 180C/hr to 540C, soak for 36min., cool at 22C/hr to 370C; 66C/hr to 40C
50mm dia.: 100C/hr to 540C, soak for 46min., cool at 13C/hr to 370C; 36C/hr to 40C

Remember this table is for spheres. For cylinders choose the diameter that is 1.5 times the diameter of your cylinder, and for flat shapes choose the diameter that is 3 times the thickness of your piece.

For other information on annealing of beads go here

Bead Annealing Schedule for Borosilicate Beads

This table is based on James Kirwin’s work on bead making with variations. This is for cold beads being heated for a secure anneal.
Up to 10mm dia: afap to 570C, soak 30 mins; anneal at 900C/hr to 500C; afap to 40C
12mm dia: 1000C/hr to 570C, soak 30mins; anneal at 630C/hr to 500C; afap to 40C
14mm dia: 1000C/hr to 570C, soak 30mins; anneal at 468C/hr to 500C; 1000C to 40C
16mm dia: 1000C/hr to 570C, soak 30mins; anneal at 355C/hr to 500C; 1000C to 40C
18mm dia: 1000C/hr to 570C, soak 30mins; anneal at 280C/hr to 500C; 840C to 40C
20mm dia: 1000C/hr to 570C, soak 30mins; anneal at226C/hr to 500C; 675C to 40C
22mm dia: 1000C/hr to 570C, soak 30mins; anneal at 187C/hr to 500C; 560C to 40C
24mm dia: 1000C/hr to 570C, soak 30mins; anneal at 157C/hr to 500C; 470C to 40C
30mm dia: 800C/hr to 570C, soak 36mins; anneal at 100C/hr to 500C; 300C to 40C
38mm dia: 500C/hr to 570C, soak 39mins; anneal at 60C/hr to 500C; 180C to 40C
50mm dia: 285C/hr to 570C, soak 46mins; anneal at 36C/hr to 500C; 100C to 40C


Remember this table is for spheres. For cylinders choose the diameter that is 1.5 times the diameter of your cylinder, and for flat shapes choose the diameter that is 3 times the thickness of your piece.

For other information on annealing of beads go here

Bead Annealing

There are two approaches to annealing beads.

One is to keep them warm as you make them and when the session is finished, anneal all the beads sitting in the kiln. Assuming you are using soda lime glasses rather than borosilicate, you need to have the kiln idling at around 500C. When you have evened the heat throughout the bead, you place it in the kiln. Gloves and other heat protection attire will be needed when you open the door/lid to put the bead on the mandrel into it.

When you have finished the bead making session, you then take the temperature up to about 520C – 540C and soak there for about half an hour – both depend on the type of glass and the thickness and shape. The object is to take the glass up to a temperature where the annealing process can work, but without being so high in temperature that the bead takes up marks from the kiln shelf. More information on the soak and annealing of various shapes, sizes and types are given in later tips.

The second method applies if you have cooled the beads in vermiculite, blanket or other means to cool them slowly and you now have a group of cold beads that you wish to ensure are correctly annealed. You need to start the kiln from cold. Place the beads in the kiln and begin the firing. You need to take the beads up slowly – not more than 300C/hr - to between 520C and 540C, and soak there for about an hour. More information is given in further tips.

In both the cases described you now have the beads with the temperature equalised throughout the bead, and the annealing can begin. The annealing is the controlled cooling below the annealing soak. It is generally safe to take the temperature down at about 80C/hr to 360C. After this point you can speed up the cool down to something like 200C/hr, or if you kiln cools slowly enough, just turn it off and wait for the temperature to come down toward room temperature. This again depends on the type of glass, its size and shape.

Variations according to glass type used, sizes and shapes follow in further tips.
Annealing of Borosilicate Beads
Annealing of Bullseye Beads
Annealing Effetre Beads
Annealing Spectrum 96 Beads
Effect of Shape
Effect of Size
Effect of Variations in Sizes

Removing Beads Stuck to the Mandrel

You may need to hold the mandrel in pliers or in vice grips while holding the bead with a scrubbing pad or jar opening rubber pad.

If this does not work, try soaking the bead and mandrel in water for a few hours. This often is enough to release the bead.

A little more drastic method is to then place the bead and mandrel in the freezer. After being frozen, the bead will most often come off as the water in the bead release thaws.

A final attempt can be made with a pop rivet gun. Insert the mandrel and operate the levers, and it will push the bead off the mandrel.

If all other things fail and you really want your mandrel back, you can warm the bead in the flame and dump it in water. It will break apart with the shock from the water. You can then clean up the mandrel for future use.

Bubble Squeeze

One of the most effective ways of reducing bubbles is to adjust the schedule to allow the top glass to slump down onto the bottom sheet before the glass is soft enough to stick at the edges and trap air. This is commonly referred to as a “bubble squeeze”.

A common method is to insert a soak at the slumping temperature of the glass. You will have found that the glass will take up the form of a simple slump at a lower temperature than more angular forms. Use this lower temperature for 30mins to an hour. You may want to extend that soak time depending on the thickness and complexity of the layup.

Another method is to start the squeeze about 55C above the annealing soak temperature and increase the temperature slowly (27-55C per hour) until you are at the slump temperature.

You can also combine the two above methods by soaking at the slump temperature for 30 minutes to an hour – or longer for thick and complex pieces – after the slow rise.

If your kiln is a side fired one, you need to be especially careful, as the edges of the glass become hotter than the centre.  Two options are available - fire more slowly, or place baffles around the outside of the piece to prevent direct radiation of the heat onto the edge of the glass.

Uneven Heating Effects

If the glass is heated unevenly, it can lead to bubbles between the shelf and the glass, causing large bubbles with thin structures, if not actually burst. This can happen especially with side or side and top firing kilns. The solution to this is to [baffle] the edges of the glass from the direct heat of the elements.

Rapid Firing Effects

Bubbles between the glass and the shelf can be caused by firing too quickly. Fast firings can cause the glass at the edge to soften early and trap air underneath the glass. At fusing temperatures the air blows a bubble through the glass. Solutions for this are described in
[bubbles between the glass and the shelf]

Effect of Combustion Gasses

Some materials will partially or completely combust at fusing temperatures. This gives off gasses which expand and blow big bubbles from under the glass.

Some kiln washes, especially for ceramics, give this problem. If you believe this is the cause, try a different brand of kiln wash or pre-fire the kiln shelf.

Sometimes organic materials have been introduced accidentally or purposely onto the shelf. Either clean the shelf of the old kiln wash, or support the glass on beads, or frit to allow the gasses to burn out before the glass slumps to trap the gasses.

Damaged Shelves

Shelves that have gouges or pits can give rise to bubbles from trapped air. Since air expands much more than glass, it will force its way out through the most plastic material. At fusing temperatures, this is the glass.

To determine if this is the problem, note where the bubbles form in relation to the shelf. If it is always in the same area, there is reason to believe it is related to the shelf. By noting the location you now have an area to inspect for damage.

If you can see no damage, it may be that the shelf is warped, or has a low spot. These can trap air, just as the pits and gouges can. But these are difficult to determine by direct visual inspection. You can place a straight edge on the shelf and look for any gap as you move the edge along the shelf.

Possible solutions are:
- Avoid fusing over the shelf "pits".
- Fill shelf scratches and nicks with kiln-wash.
- Mend the shelf with cement fondue or other refractory materials.
- Fire on fibre paper - this will provide an escape path for the air.
- Flip warped shelves, as the opposite side is likely to be equivalently bowed, but in the opposite direction. The degree of bowing is imperceptible, so will not affect the appearance of the fused result.
-Grind the shelves flat. This can be done commercially with a milling machine, or you can do it manually. Place two shelves with their concave faces together with some sandblast grit between. Rub the shelves together and this will reduce the convex areas on each to flat.

Bubbles Between the Glass and Shelf

Eliminating the bubbles that can occur between your kiln shelf and the glass is important because these are the bubbles that can rise up through your work, blowing a large hole through the entire piece – Australians call these space helmets.

Common causes relate to damaged shelves, firing too rapidly, uneven heating, and combustion gasses.

Bubbles Between Layers – “Flip and Fire”

Another approach to avoiding bubbles is to plan on two firings. This works well for pieces that have multiple layers, with glass or other inclusion in the middle.

For the first firing, put the middle pieces flat on the kiln shelf with one layer of glass on top. Take this to at least a tack fuse, although full fuse temperature is better as there should be no remaining gaps for air to be trapped within. Now turn this over and clean it well. Place this part in the kiln with the middle layer up. Place the top layer over this piece – now right side up – and take to the full fuse. Remember that now you are firing a thicker piece than in the first firing so take the temperature up more slowly.

This is most often applied to three layer pieces, but in principle can be applied to any number of layers.

Using baffles
Supporting the edges
Design elements
Arrangement of glass sheets

Bubbles Between Layers – Baffles

Bubbles are often caused by the edges of the layers sealing before the air can escape from between. This frequently happens in side fired kilns, and top and side fired kilns.

Set up heat baffles around the edges of the sheets being fused to decrease the chance of the edges getting more heat than the centre and trapping air between layers. The baffles can be made from kiln furniture, strips of fibre board, cut pieces of old kiln shelves, etc. - anything that will witstand the top temperature.

Arrangement of glass sheets
Designing for fewer bubbles
Edge supports to reduce bubbles

Bubbles Between Layers - Supports

A common way to reduce bubbles that appear between layers of glass is to support the edges of the glass allowing the middle of the top sheet to sag before the edges so pushing the air in front of the collapsing glass.

You can do this with small beads - especially useful for large glass sheets. These beads are prepared in advance by firing small pieces of glass during a previous fuse firing. The glass draws up into a bead-like structure. You place these beads around the edge of the glass sheets. Use glass that is the same colour as the base glass to avoid strong colour spots in the finished work.

Make sure you advance the temperature slowly enough to allow the glass to slump from the middle outwards, allowing the air to escape. Note that even clear beads will leave a trace, so design your work to take advantage of these faint marks.


Another method is to put small pieces of frit every few centimetres around the edge of the bottom piece of glass. Place the top piece of glass on top of these spacers. When fired, the middle of the top sheet will sag first and the area of contact between the two sheets will spread from the middle pushing the air out as it goes, just as with the beads. But the evidence is not so marked as with the use of beads. However the frit is not so useful on large pieces.

Design factors
Arrangement of layers
Using baffles

Fibre Papers

As there always is concern about the health effects of ceramic fibre paper, the report I prepared for a supplier may be of interest.  It can be found here.

Bubbles Between Layers - Design

Design your work to minimise the possibilities of trapped air.

One way to do this is to use strips. Lay thin strips of glass on edge and fuse these together, instead of layers stacked on each other.

Another is to design work with many smaller pieces, rather than large ones. These create more pathways for air to escape.

Some advocate cutting the bottom layer in several strips to allow the air exit spaces from between the glass layers.

Note that all these methods leave marks of where the edges of the cut glass was, so they need to be planned to fit with the design.

In general terms, you need to think about how the air will move out of the piece. Are there places where there is no escape for the air? Allow a channel for the air to move from the centre to the outside.

Glass arrangement considerations
Supports
Using baffles