- 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
Friday, 26 August 2011
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
Tuesday, 16 August 2011
Thursday, 11 August 2011
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
Wednesday, 3 August 2011
Monday, 1 August 2011
- 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)