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refiring thick slab

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refiring thick slab

Postby rfreedfl » Wed Aug 30, 2017 9:37 am

I have fired a 1" thick slab and want to add a decorative layer to the top of it, either tack or soft fuse. Do I need to use the same firing schedule, long annealing time and slow cool down, as I did with the initial firing. If so, how will this affect the outcome of my tack fuse on the top layer.
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Re: refiring thick slab

Postby marykaynitchie » Thu Aug 31, 2017 9:04 am

You will need to use a longer annealing schedule. Are you using Bullseye glass?

When a project is an inch thick, and you are adding more elements to it, your concern to get the right firing schedule is understandable! There is more to lose than in a 6mm thick project. Good thing you are giving this new firing some thought.

Here are some resources for you to learn more about tack firing elements to a previously fired piece.

Tips for Tack Fusing (subscription video)
https://videos.bullseyeglass.com/videos ... ck-fusing/

Annealing Thick Slabs (free article)
https://www.bullseyeglass.com/methods-i ... slabs.html

Glass Fusing Basics (free video)
https://videos.bullseyeglass.com/videos/fusing-basics/

Firing: Basic Applications (subscription video)
https://videos.bullseyeglass.com/videos ... lications/

Firing: Basic Principles (subscription video)
https://videos.bullseyeglass.com/videos ... rinciples/

TechNotes 4: Heat and Glass (free article)
https://www.bullseyeglass.com/methods-i ... glass.html

If you want to describe your project in more detail, and propose a firing schedule, I am confident that one or more of us can offer feedback.

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
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Re: refiring thick slab

Postby rfreedfl » Fri Sep 01, 2017 10:25 am

Yes, I am using Bullseye Glass. I have 2 slabs 1 1/2"x7"x 1" high (originally 9 mm layers) successfully fired. I am adding some small 2 layer decorative pieces to the top and want to achieve a tack or soft fuse. Here is my proposed schedule based in what I used to fire the slabs. I am keeping them dammed.

ramp hold temp
250 20 1000
250 30 1150
50 85 1250
100 5 1300 (or whatever temp visually appears to achieve tack fuse)
Full 4 hrs 900
27 0 800
49 0 700
162 0 70

Thank you for your help
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Re: refiring thick slab

Postby marykaynitchie » Tue Sep 05, 2017 9:55 am

You describe your decorative elements as "two layers". Does this mean that they are about 6mm thick, on top of the slab, before firing?

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

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bit.ly/BullVideos
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Re: refiring thick slab

Postby rfreedfl » Thu Sep 07, 2017 5:09 am

Yes, that is correct.
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Re: refiring thick slab

Postby marykaynitchie » Mon Oct 09, 2017 9:16 am

I was waiting for a consultation before posting a reply:

All together, your piece on this firing is about 32mm, or 1.25 inches thick. Because the thickness is uneven, you need to anneal for twice the thickness of an uniformly thick piece. Therefore, you need to anneal for a 64mm, or 2.5" thick piece.

Here is a screen capture of the portion of the chart "Annealing for Thick Slabs" for your reference. The bottom row has the info you need for your piece.

Screen Shot 2017-09-15 at 2.38.45 PM.png
Screen Shot 2017-09-15 at 2.38.45 PM.png (89.1 KiB) Viewed 22183 times


You are suggesting the following cycle:
ramp hold temp
250 20 1000
250 30 1150
50 85 1250
100 5 1300 (or whatever temp visually appears to achieve tack fuse)
Full 4 hrs 900
27 0 800
49 0 700
162 0 70

According to this chart, and the video cycles, you could use this cycle:
41/hour to 1000, hold for 20 (That is the cooling rate for twice the thickness of the one-inch slab by itself.)
600/hour to 1250, hold for 10 minutes or when you can visually confirm that the glass has softened enough
AFAP to 900 (Keep door closed--no peeking!)
4.3/hour to 800
8/hour to 700
26/hour to 70

This will take about 70 hours. It is a conservative schedule.

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
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