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Hello, looking for some tips on how to anticipate fuse shrinkage while fusing Bullseye glass. All thoughts/comments welcome!

I'm getting ready to make 2 fused pieces. The final sizes of the pieces must be 48,1 x 33 cm (18.9 x 13 inches) and 58,1 x 32,9 cm (22.9 x 13 inches), give or take a smidge. These fused panels will fit into windows in an apartment interior, in the bathroom door and the bedroom door.
The basis glass sheet is 3 mm thick and then there will be design-flowers built up on that but not overall on the glass. Some of the final piece will be 3mm thick, in some places 5-6 mm thick. I intend to leave the edges of the glass free of materials so that there's not an issue with placement.
I've done some small tests in advance to see how I want to make the design and at what temperature. The final pieces will be fired at 785 C.
Of the two tests I've done at 785 C:
- for the first test the glass size pre-firing was 18,2 x 16,7 cm and the size post-firing was 18 x 16,5 cm
- for the second test the glass size pre-firing was 18,3 x 14,4 cm and the size post-firing was 18 x 14,2 cm

Is there any way I can reliably scale up the sizes so that I get just the right amount of shrinkage ?

Thanks in advance!
kind regards,
Lisa

Shrinkage is based on volume of glass, not manufacturer... If the glass is not a uniform 2 layers thick you will get shrinkage! You have a few factors to deal with eg: top temp, top temp. hold time, amount and location of second layer design...... Your safest bet is to fire oversize and grind/polish to size.

Thanks Don!
What about making it significantly larger and then cutting to size? Any thoughts?

Yes that would also work if you don't have a WBS. An extra 1/2"of base glass on each of the 4 sides would be easy to score and remove.