Freeze and Fuse

The object of this technique is to make a shaped piece without use of a refractory mould. It is applicable to small items.

You can use jelly, soap, candle, etc. moulds. They can be rigid or flexible. They should be without undercuts and have a draft, which is why jelly, soap, and candle moulds are so suitable. Be careful of the size, as a large amount of frit can be required even for a small mould.

Some people use only powder for this process. I use a 50/50 combination of powder and fine frit. You can use clear frit with powder. If you do so, you need to measure out the appropriate amounts.  Then put the frit and some water into a container with a closure. Close and shake to wet the frit. Then add the powder and shake again to ensure the powder adheres to the frit. Once thoroughly mixed, add more water to make a thick slurry.

Pack the mould with the mixture. Then using absorbent paper towels firmly pat the contents of the mould as dry as you can. Place the mould in the freezer for at least a couple of hours, or for large ones overnight.

When frozen, remove from the mould and place on the kiln shelf. The shelf needs a separator which can be kiln wash or fibre paper. Some leave the piece to thaw out and some more of the water to evaporate.

Whether you fire immediately or let the piece thaw and evaporate, you need to fire slowly to 100C and soak there until no more moisture is evident to avoid creating pockets of steam that will blow the piece apart. After that you can fire as normal for an initial firing of a two layer piece.

The piece will shrink a bit during the firing, but it is safe to anneal for the original thickness of the frozen piece. If you have a large piece or one with lots of variation in thickness, you should use at least the next thickness up from the Bullseye tables for annealing thick pieces. Sometimes you should use two steps up.

Further information is available in the ebook Low Temperature Kiln Forming.

Fibre Board for Kiln Shelves

Some advantages of fibre board:

• It is light weight making it easy to move.
• Fibre board has very good cooling characteristics as it doesn't hold the heat the same way a mullite shelf does.
• The board is fragile, but with care can last years.
• Fibre board shelves do not thermal shock as ceramic based shelves can.

Considerations for use:

• If it will be moved it needs hardening.
• It needs repeated sanding and hardening for a really smooth surface. Alternatively you can smooth on something like batt/kiln wash or alumina hydrate for each firing.
• It needs to be supported on kiln posts at 100 mm intervals.

You need to use dust masks when ever working with fibre board.

Some disadvantages of fibre board:

• The board can warp over time even when supported every 100 mm.
• The board will warp over time if placed on the kiln floor.
• The board needs to be thick - at least 25mm, thicker for larger kilns.
• It can't be scraped clean of batt/kiln wash.
• Ceramic fibre board is possibly not much cheaper than mullite shelves.

COE

CoE

CoE is an abbreviation for coefficient of linear expansion. This has a very specific definition which is not widely understood.

The "linear expansion coefficient" is determined by a laboratory test which expresses the average expansion rate from room temperature to 300ºC. It ignores the more important range of expansion for determining compatibility for fusing and the expansion through the annealing and softening ranges as this graph shows.

It also ignores viscosity, an important element in determining whether glasses will "fit" each other on fusing. Not all "90" expansion glasses are compatible.

The two major factors in a fusing compatible glass are expansion characteristics and viscosity. These need to be in balance with each other within one piece of glass and with other pieces of glass with which they are combined. There are other factors of course, because glass chemistry is very complicated.

Overlapping Joints

Overlapping Joints in paneled windows

In many installations of tall windows, such as churches or tall sidelights, there is a requirement for handling and transport that the window be built in panels, each of which sit on top of the other. There are some considerations about the design and installation of such windows.

The design has to allow for the additional thickness of at least two hearts at the joins of the panels.

The leaves of the upper leads should always overlap the lower leads to be able to shed water from the rain so it does not migrate inside.

There should be wide heart “H” leads on the bottom of each panel. These should be 12mm or 16mm wide heart flat leads on all except the bottom panel where the normal 5mm heart can be used.  The wide heart lead allows easy placing of the upper panel onto the lower one.  It is possible to open the leads of a standard heart lead, but it is much easier to use a wide heart lead.

The top leads on each panel should be flat leads of 10mm or “U” lead. This is largely preference. If you use “H” leads at the top, you should fold the leaves over, or cut them off, depending on the allowance in the design.

The openings should have glazing or saddle bars placed at the levels where the panels join. These need to be tied to the panels with tie wires soldered onto the panels. The ties on the panels should be soldered so that the ties on the bottom of the top panel point downwards, and the ties on the top of the bottom panels point upwards.  It is important that the soldering of the tie wire on the bottom panel is very flat and low enough to avoid interfering with the flange of the upper panel and to allow the easy setting of the top panel over the joint. It is also worthwhile to put a loop in the soldered end of the tie wires so they do not pull out of the solder joint.

Once you are certain of a good fit, set the upper panel down onto the lower one.  Dress down the opened flanges of the upper panel over the lower one.  Then draw the wires from the upper panel down behind the saddle bar, the lower wires up behind the saddle bar, fold over them over the saddle bar, twist firmly.  Cut the ends to uniform lengths and fold back the twist up and over the bar.  This secures the panels, draws the two panels together and provides lateral support to the window.

It is not necessary to putty the joint of the panels, as the flange of the upper lead is sufficient with a little dressing of the flanges flat to the lower panel to avoid any ingress of water.

Old Cement

Removing Old Cement from Glass

Composition of old cement

Old cement can have a variety of components. One is red lead, another is portland cement. Both create different problems, but both require that all removal of old cement should be done with breathing protection.

Mechanical removal

Removal of old cement can be attempted first with mechanical means. Stand the glass on edge and use a lead knife almost parallel to the surface of the glass to knock off the old cement. This works most of the time. But if the bond is too strong and begins to cause chipping of the glass, you need to switch to another method.

First consider whether the whole panel needs to be re-leaded. It may be that only portions require re-leading and so the remainder should be left in its original leads. This is especially true where there is painted glass, as you do not want to loose the original painting.

Chemical removal

If mechanical removal is not working you need to consider chemicals.

Lye will dissolve linseed oil but perhaps also the paint and so should be used locally only and with extreme care and caution. Testing on unobtrusive areas is required.

Another way to soften the linseed oil is with heat and for this a steam generator works particularly well turning hard putty into the consistency of soft cheese which can be scraped off.

If it actually is Portland cement creating the bond then hydrochloric acid is what bricklayers use to dissolve and remove mortar stains from brickwork. Carefully paint it on the old cement and it should start fizzing and dissolving straight away.

Precautions

What ever you decide to do, test first with some of the glass that will be discarded and confine your chemicals to the cement only and don’t spread them over the entire piece of glass. Wear a respirator at all times during the removal process.

Radiating Lines

In leaded glass designs it is important to avoid lines radiating from a single point.

Good design will avoid multiple radiating pieces from a single point of origin.

Among the reasons for avoiding radiating lines are:

• It is important to reduce the number of lines that meet in any design to avoid the big bright solder place in a panel.
• It makes for large solder blobs, especially on leaded glass panels, and therefore provides a focus where one may not be wanted or required.
• It also is a point of weakness as the multiple thin or tapering pieces of glass are liable to fracture. 
• Also the difference between the harder solder and softer lead came leads - over time - to cracks in the lead at the edge of the thick solder blob.

There is a difficulty in adapting single radiating points in a drawing to the practicalities of the medium of glass. Examination of older panels (in either copper foil or leaded technique) will show up some of the problems of thin tapering pieces, especially in the Victorian era where tapered pieces where in their glory. Almost always, there will be broken tips. They seemed to compensate for tip stress by making the pieces with narrow tapers smaller than some of the other wider pieces. Even then, there are a lot of broken ones seen. It is the nature of glass, and goes back to knowing how the glass will react to the conditions you create.

Methods of avoiding tapering pieces lie in the design.

You can't use long tapered pieces in larger panels, without modification for the structural reasons outlined above.

Also you can't make a neat termination by joining half a dozen tapers at one point. Your piece will not look exactly what it looks like when you drew it out with a pencil. You can pencil in a termination with six points, ending at one point and it may look good, but try drawing it in with a felt tip pen almost 6mm wide, which shows for what the solder has to  cover, and see what that point looks like then. For copper foil a 2-3mm wide line will demonstrate what will be seen after soldering. You may not be pleased with the large blob at the termination.

No one can teach one easy fix for everything you will encounter, so the answer starts with the design, before you cut and foil, or fit the came to the glass. Art is not about the physical placement of what you see in your mind, as much as it is about the "illusion" you are creating that you want others to see. That starts with the design, and avoiding incorporating something that you know is going to give you a problem. 

Measuring Openings

Measuring rectangular openings

Timber and metal openings can vary in their dimensions. So measure each opening at the top and bottom, and at the left and right as well as the middles of each side and top and bottom.

To be perfectly sure the window has right angles – is square – take the diagonals from opposite corners, e.g., top left to bottom right and top right to bottom left. These measurements should be within 5mm of each other for the window to be considered square.

You can check for ”squareness” with a try square, although that is not completely accurate.

Templates

If it is not possible to tell where the right angles of the opening are, a template is called for. The material to be used for taking templates should be stiff, easy to cut, unaffected by moisture, and relatively inexpensive. This eliminates paper and some cardboards. If you can find stiff corrugated cardboard this works well. Mounting board works well too, but is expensive. Foam board is excellent, but also expensive. Hard board or other thin pressed board is inexpensive but difficult to cut with a knife. Thin plywood is also a good material for templates, especially if the opening is relatively regular. The more complicated the opening, the more cardboard, mounting board, or foam board becomes useful for its ease of shaping to the opening.

What ever material you use, you must mark which is the interior and exterior and for further checks, which is left and right. Fit this template into the opening to make sure it fits into the opening smoothly. This template will form the external extent of the built window when it is installed into an opening with a rebate.

Where the window is to be fitted into a channel, as in stone, you need to make the template of stiff material so you can determine the panel can be installed and that there will be enough of the panel within the stone channels to ensure the stability of the window in the future and still be able to manipulate the leaded panel into the opening.

Encapsulating Glass

Points to note when making panels for encapsulating leaded panels in double glazing units.

In building a new panel, the perimeter should be of “Y” came. This allows the double glazing spacers to be placed on either side of the leg of the “Y”, incorporating it into the structure of the whole unit.

The tolerances for double glazed units are much less than for single glazed wooden units.

If you decide to use mastic, it must not be linseed oil cement, as the oxidisation process produces a condensate that fogs up the interior. Use a butyl putty instead.

It is also possible to finish the panel without any mastic under the leads, as the double glazed unit will provide the structural support. You do need to dress all the flanges of the lead to the glass to avoid light showing around the edges of the glass.

Finishing the leads should be with a polishing brush only to avoid introducing chemicals in a closed atmosphere. The polishing brush will bring up a dark colour on the leads and solder joints with repeated light brushing. This also is an indication that the solder jointing should be as neat as possible with small flat joints.

Bottle slumping

Results

Devitrification is a major problem on bottle slumping. Some means of reducing the problem are

• clean labels off thoroughly
• remove all adhesives
• scrub the whole bottle and polish dry
• apply a devitrification spray before firing.
• Spend as little time in the devitrification range (700C – 750C) as possible
• Vent the kiln up to 540C if you are using fibre papers
• sandblast off the devitrification and fire again if the devit is slight
• in severe cases of devitrification, throw the bottle away.

Champagne and large bottles of sparkling wine split easily due to the differences in thicknesses. Firing of these needs to be very slow until you get past 715C.

Bottles with printed labels need particular care. The enamels used in the printing may contain lead and any other elements in the paint may contaminate your kiln.

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Bottle Slumping

Firing

The amount of slump you want will determine the top temperature combined with the rate of advance.

You have the choice of firing slow and low or fast and high. If you choose the former, you can also choose a lower final temperature. As a starting point for considering your firing schedule you can assume that bottle glass is very similar to float glass. This means that you can start with an annealing temperature of about 548C and a softening point of 720C. The strain point is around 510C, so all the annealing needs to be finished by that temperature.

Bottle glass is fairly robust, so an initial rise of 150C/hr to 600C may be slow enough, considering the differences in thickness that most bottles exhibit and then faster to your top temperature. A little experimentation is required. The minimum temperature required for a slump will be around 720C. The slumping temperature you choose depends on how fast you want to achieve your slump and how flat you want the result to be. Slow slumps can be done at around 720C, but if you want faster or flatter you need to consider temperatures around 770 -790C. You will need to observe to determine what temperatures are best for your desired results.

Annealing needs to be done carefully for two reasons. You do not know how consistently the glass has been made and you have a range of thicknesses involved in the now slumped piece. So it is safest to assume the piece is now about 20 mm thick. This would require a 3 hours soak at 550C; an initial annealing cool rate of 25 C/hr to 495C; a secondary cool rate of 45C/hr to 440; and a final cooling rate of 150C/hr to around 50C. If the bottles are clear or light enough, you should do a stress test on them by placing the bottle between polarised filters and over a light source. This will tell you if you have annealed properly.

You also need to consider whether you can fire bottles from different brands of drink and different parts of the world together. Some say don't try it. Others say there is so little variation in glass the world over that careful annealing will compensate for the differences. Experimentation is the only way that you will be able to tell.

Allow a day after firing before any cleaning or washing of the bottles is done.