Friday, 15 February 2013

Single Layer Firing


Preparing a Single Layer for Further Kiln Work

There can be circumstances where you do want to fire a single layer in building up your project. This is more often difficult on rectangular than round pieces.

Some of the considerations are:
Temperature
Heat work
sizing
Cleaning after firing

Firing a 3 mm piece to anything over a laminated tack fuse normally leads to the edges drawing in creating a “dog bone” effect and often leading to bubbles in the interior at higher fusing temperatures. So one approach is to fire at low temperatures and accept relatively sharp edges on the piece.

Diagram of the full fused results of different thicknesses 


However the concept of heat work can help in this situation. Glass reacts to the accumulation of heat, so that slow advances or long soaks can achieve the desired results at a lower temperature without – in this case – getting the “dog bone” effect. This does require a bit of experimentation. Keep good records of all the stages of experimentation as the effects achieved with various combinations of temperature and time will come in useful later.

It is possible that using the concept of heat work will not be sufficient to achieve the desired results. Then you need to consider placing your design in the centre of a larger piece. Fire this to the lowest possible temperature to achieve your results and then cut the fired piece to size. You will need to fire polish or cold work the edges to get a suitable finish on the edges.


The central white piece shows the results of single layer firing that could be altered by the above technique


If you are going to re-fire any of these single-layer pieces, you need to clean them very well. Any dust or other contamination will be incorporated into the final piece. This is especially true if you are combining a flip and fire technique with this single-layer firing.