- Is the glass trapping the mould? This happens most often when the glass is draped, especially over ceramic moulds.
- Has the glass been fired high enough to fuse to the mould? If you have fired the glass to tack fusing temperatures, you may find more occasions when the glass sticks slightly or firmly to the mould.
- Is the mould trapping the glass? This can happen when slumping into a steep sided steel mould. Occasionally a steep sided ceramic mould will show the same effect.
- Has the separator been too thin or failed? If none of the previous elements apply, it may be that the separator was too thin or has been fired to tack fusing temperatures in a previous firing.
Wednesday 31 August 2011
Glass Stuck to Moulds
Friday 26 August 2011
Aperture Drops Finishing
For most aperture drops and for most people, it is desirable to remove the rim. To have successful drops without rims, you most often need to have access to cutting and polishing equipment.
You can use a tile saw or band saw to cut off sections of the flat rim and then a linisher to grind the edges to round, followed by polishing. This will give you a thick rim.
If you want a thin rim, you will need to cut through the drop at the top - visualise a cut at right angles to the length of the drop. Usually tile saws are too aggressive for this. If you can find a band saw with a high enough clearance, you could gently separate the rim from the drop after having reduced the size of the rim to make the use of the band saw more easy.
In both cases you must grind and polish the edge of the rim to give a finished appearance. Fire polishing is not possible as the drop would collapse long before the rim was smooth.
Sunday 21 August 2011
Aperture Drops Annealing
Tuesday 16 August 2011
Aperture Drops - Stopping the Drop
Thursday 11 August 2011
Aperture Drop Observation
This kind of firing absolutely requires observation of the progress of the drop. Ideally you would set up the firing surface where you can peek at it during the firing as well as observe the bottom of the kiln or the shelf – which ever you are firing upon.
I you have to choose, then the bottom of the kiln is the most important place to have clear observation lines. Even if you do not want the drop to touch the shelf or bottom of the kiln, you will need to observe how far the drop has progressed.
Thus, planing for the placing of the supports and other elements of the drop are important. Support posts should not obscure the view of the drop, for example. The whole set up should be placed far enough back in the kiln to see the shelf/kiln bottom where the glass will touch down.
If you do not want to have the drop touch down onto a surface, you need to set up a “witness” to indicate how far the glass has fallen. This can be some pieces of fibre stacked up so that your view through the peep hole to the top visible surface of the “witness” will tell you that when the glass touches that line of vision, it has reached the desired length.
You need to patient, as the soaks can be two or more hours long for a low temperature drop.
Saturday 6 August 2011
Aperture Drop Placement
Wednesday 3 August 2011
Grinder Head Grub Screw
Monday 1 August 2011
Aperture Drops Firings
- one is to heat at a very slow but consistent rate. After the annealing point has been reached the speed can be increased.
- the second is to go a bit faster, but with soaks at three or more intervals in the heat up. After each soak the speed of advance can be increased a little. The soaks should be from 15 to 30 minutes, depending on the speed of heat up.
- aperture size
- weight of glass
- speed of advance to forming temperature
- glass used (to a lesser extent)
Friday 22 July 2011
Aperture Drop Supports
Sunday 17 July 2011
Aperture Drops – Length of Drop
glass required.
The thinning effect of the stretching can be influenced by both the temperature and material of the supporting material.
Tuesday 12 July 2011
Aperture Drops Introduction
The height of the drop from the shelf.
Material of the supporting ring or material.
Initial firing speeds
Height in kiln and relation to the distance from the heating elements.
Observation of the progress of the drop.
Arresting the drop
Annealing and cooling.
Finishing the resulting drop.
The above instalments will discuss these in turn.
Thursday 7 July 2011
Scoring Opalescent Glass
Saturday 2 July 2011
Care in the Operation of Soldering Irons
Monday 27 June 2011
Grinder Bits
Wednesday 22 June 2011
Replacing Grinder Heads
Friday 17 June 2011
Leading Nuggets
Sunday 12 June 2011
Edges for Copper Foil
You do not need to use wider foil on the edges, but I have often done so to give the edge just as much "line value" as the internal beads. However this needs to be planned from the beginning. If you simply add a wider line on the outside, many times you will compromise the integrity of the design at the sides. You need to cut the glass a fraction larger to accommodate the thicker foil. Two millimeters added to the outside edge should be enough.
Wednesday 8 June 2011
Foil not Sticking on Edge
I’m working on another irregular shaped suncatcher and I have just completed the soldering. Now I've found one small section the copper foil is not sticking. How can I fix this?
The adhesive on copper foil tape is not a permanent one. It only sticks to the glass long enough to apply the solder to the foil. The heat of soldering often degrades the adhesive so much that it no longer sticks. What holds the solder down is the solder bead. So you probably do not have a full bead on the edge. Placing a bead on the edges of pieces is difficult but you can find a method here.
You can make the edge beading a bit easier by putting thin copper wire around the edge of the piece. This strengthens the whole piece. It allows you to attach a hanger without risk of pulling the whole suncatcher apart. It also allows you to form a bead on the edge more easily.
The bead formed on the edge curves around to the front and back faces allowing the solder to hold the copper tape more firmly to the glass.
Saturday 4 June 2011
Tie Wires
The tie wires should be securely soldered to the panel at solder joints. Placing ties elsewhere leads to the tearing of the lead. The soldering of the tie wires requires more heat than simply soldering the lead joints. The tie wire needs to be heated enough to melt the solder of the joint to which it is being attached. Then an additional dot of solder needs to be added so that the wire cannot simply pull out from the joint by being only sweated to the joint.
At installation, when the panel is fully seated in its opening and fastened by nails or sprigs, pull the tie wires out at right angles right at the edge of the solder attachment before twisting the wire. Do not use any more than firm pressure. Then you are ready to cross the wires over the glazing bar. This ensures there is no excessive give in the copper tie.
Do not over tighten the tie wire twist. Only twist until snug against the bar. Then continue to twist the loose ends until you have them a satisfactory length. Cut off the twist rather than the tail ends to provide a neat finish. Then tuck the twist under or over the bar, just as you desire.
Tuesday 31 May 2011
Installation of Glazing Bars
The holes on one side should be at least 5mm deeper than the other. For a really secure attachment one side should be at least 15mm deep and the other 7-10mm. This allows a significant amount of wood to seat the bar. The bar should be at least 10mm longer than the opening is wide.
The hole you drill should be 1mm larger than the bar diameter. This will make moving the bar easier. Additionally, the ends of the bars should be filed to remove any roughness. Also greasing the ends of the bar with tallow or candle wax will ease the movement of the bars.
If the bar is to be installed inside sash windows you can ease the installation by determining the height of the hole to be drilled by presenting the panel to the opening and marking the frame where the bar is to be attached to the panel. Drill the hole so the edge of it is flush with the rebate. This allows you to use a chisel to open the hole enough to allow the bar to be placed in the socket now prepared. In these cases the bar needs to be no longer than the opening.
The installation should be completed by forcing putty into any gaps left between the bar and the hole. This will stiffen and help to firm up the bar’s attachment to the frame.
Friday 27 May 2011
Cementing Panels
This photo shows how the putty filled the space above and below the glass but not between the glass and the heart of the came.
Monday 23 May 2011
Jewellery-scale Ovals
Cut a rectangle the length and width of the oval you want. Then groze the corners to the approximate curve of oval you want. Do not worry about the little inaccuracies of the curve. If it is the curve you want, the heat of a full fuse will even out the edges into oval you want. Clean the glass, assemble and fire to your normal full fuse temperature. The result will be a smooth edged oval of the shape you grozed from the glass. Of course anything less than a full flat fuse will produce a piece with some of the inaccuracies that you grozed into the glass.
If you do not go to a full fuse, or are using only 3mm thickness of glass, this will not work.
Monday 16 May 2011
Effect of Glass Weight on Slumping
When slumping you are making use of the combined effects of gravity and the increasing softness of the glass. The same thing happens when you have a thick piece of glass as when you have a large span in the mould. As the weight of the glass increases, the temperature at which it will begin to slump is decreased. There is an inverse relationship between the weight and the slump temperature just as there is between increased span and slump temperature.
A 3mm piece will take more time or more heat to fully slump into a mould than a 9mm piece will into the same mould. Observation will give you the information on what the temperature differentials are.
Monday 9 May 2011
Bowed Glass for Cabinets
You can make a mould and do a slump.
However, you should consider doing a drop out or aperture drop. Normally these are thought of as circular, but they can be of any shape you want. The reason for making them as a drop out is that the surface of the bent glass will be completely unmarked.
I have made these several times for antique dealers. To do it, make a rectangle in fibre board about 10mm larger than the glazing size. Place a piece of glass about 40mm larger than the rectangular hole and fire. You need to watch. It will begin to slump at around 520C - or less if it is not float glass. You need to go slowly so the glass does not drop too much.
You will know from the existing pieces how deep a drop is required. Measure that and place a witness to determine when the slump has gone far enough. This can be a piece of kiln furniture with fibre paper over it. It can be a reference point on the far side of the kiln. In my case it normally is a stack of fibre board pieces with fibre paper on top to build it up to the correct height.
When the glass is just about to touch the witness, flash cool the kiln to just above the annealing point and close the kiln. If the temperature rises back into the forming temperature range, flash cool again. Twice should be sufficient to ensure that the glass does not move any further.
Monday 2 May 2011
Cutting Flashed Glass
What is more important is to observe that flashed glass often has a bow. If you place the glass on the bench, you may find that it rocks or sits up from the bench. If you cut the glass on the convex side, that is the side which is not resting on the bench except at the edges, you may find that you break the glass during the scoring, unless you are using the lightest of pressures. It is more certain to get a good break if you score the glass on the concave side - that is where the edges are slightly raised from the bench. So the important element in deciding which side to cut is to score the concave side whether that has the flashed colour or not.
This does not occur with all flashed glasses, and is more important on large sheets than small ones. On the small ones, the curvature is so small as to be immaterial.