Lamination in kiln
forming is the adhering the glass pieces together without changing the shape of
the glass. On a laminated piece the
edges of the glass will still be sharp but cannot be pulled apart. Each manufacturer's glass will have slightly different
lamination temperatures and it will be affected by the length of soak.
How do I find the lamination temperature?
Observe
Make your chosen layup
in clear glass.
Peek at your glass
at frequent intervals from 550C. The rate of advance should be slow, say
150C or less. When it is observed the edges are just beginning to round, you know
you have the high-profile tack temperature for that rate of advance.
On another firing of
the same setup and rate of advance, soak at 20C lower than the previous temperature
for 60 mins. You need to keep peeking during the soak to ensure the edges
remain sharp.
When you see the
edges begin to round, you need to advance to the cool and record the length of
the soak used. You will need to shorten
that soak by the interval of your peeking.
If you were peeking every 10 minutes, reduce the length of the actual
soak given by 10 minutes for the next firing.
These three firings
will give you a schedule for laminating glass together for your chosen layup. Other layups will require slight variations
which will also require observation to determine how much change from the original
schedule is required.
Anneal and cool carefully
Do not forget to schedule
the anneal soak and cool for at least 2.5 times longer than for the thickest part.
The reasons for the
longer soak and slower cool are:
- The glass pieces are not incorporated with each other, but only at the interfaces.
- The pieces will react to cooling in different ways.
- Different colours have different viscosities and different contraction rates.
- The shading effect of one piece on top of another is intensified.
- There are right angles between the base and the stack of glass above.
All these factors make it important to ensure all the glass is at the same temperature (the anneal soak) and that the pieces that make up the whole cool at the same rate even when shaded.
revised 20.2.26
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