Lamination

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 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 twice longer than for a tack fuse each time.  This may make the soak four or more times longer than for a full fuse.

The reasons for the longer soak and slower cool are:

·         The glass pieces are not incorporated with each other. 

·         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.

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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.

Further information is available in the e-book: Low Temperature Kilnforming.