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Getting the most out of Striker Colors

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

Re: Getting the most out of Striker Colors

Postby mattt » Fri Mar 03, 2017 7:33 am

Gold hold - should we then reduce our top fusing temperature?

I've found that when I include the "gold hold" on the way up to fusing temperature, my glass then over-fires. causing dog-boning at what should be a tack fuse.

I was making a series of large panels, 30 x 60cm incorporating violet and gold purple; thicknesses varied from 4 to 7mm thick, so I annealed for a thickness of 14mm.

Given that my kiln is around 10 years old & fires hotter than the read-out on the controller, I normally tack fuse at what my kiln thinks is 720° centigrade. My kiln schedule (in centigrade) was thus:-

222°C / hr to 627°C; 30 minute bubble squeeze.
222°C / hr to 663°C; 2 hour hold to strike the gold bearing glass.
333°C / hr to 720°C - tack fuse temperature in my kiln - 10 minute hold.
As fast as possible / "full" down to 482°C. 2 hours 30 minutes anneal hold, then
40°C / hr to 427°C, then
72°C / hr to 371°C, then
240°C / hr to 25°C. End.

Without the 2 hour hold at 663°C, this would have given me a good tack fuse. My question is, if the extra heatwork involved in striking the gold-bearing glass causes the glass to fuse at a lower temperature, how much should I drop my top temperature by? If I want an intermediate fuse, I'd normally go up to 750°C, or I full fuse at what my kiln thinks is 780°C, so should I be dropping my top temperature by 40°C or so? :?
mattt
 
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Re: Getting the most out of Striker Colors

Postby alfeze » Sun Mar 12, 2017 3:37 am

All the videos talk about cumulative heat. Does that mean that there is a mathematical way to address matt's question? Ie he did 4hrs at the hold not 45mins is it possible that because there was already the earlier bubble squeeze so he did need more than the 45? Its got to be very tricky to experiment for something that large and thick?
I know that some write that we should look in the kiln... during say that tack fuse stage? Would he have been able to see that it was already fused at the start of the higher temp?
Ive done some stuff that worked using shelves to get higher and lower temps in the same kiln firing but it was definitely more luck than judgment:-) And then just repeating the same thing again. As a recent convert from computing world i thought it good that there seemed to be chance involved.. happy accidents.. but maybe its all just lack of experience and knowledge on my part:-) boy is learning fun here! :D
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Re: Getting the most out of Striker Colors

Postby devoncohn » Sat Sep 05, 2020 2:10 pm

Reviving this thread because I've been searching for suggestions on how long to hold gold-bearing strikers at 1225 F and I see two different numbers.

Is it better to hold for 2 hours (as seen online in the Bullseye section "About Our Glass" http://www.bullseyeglass.com/cranberry- ... t.html?p=3),

or for 45 minutes as suggested in this discussion (marykaynitchie@bullseyeglass.com: Gold-bearing striking glasses can appear pale or colorless in the cold sheet and "strike" or change significantly to target color when fired. To promote proper color development in this group of strikers, we suggest a 45 minute hold around 1225 degrees Fahrenheit on the way up to process temperature.)

I'm also wondering if I can fuse the sheet in a "pre strike" fuse to 1225 F to develop the color so I know what it will look like before I assemble my project?
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Re: Getting the most out of Striker Colors

Postby mattt » Sun Jan 31, 2021 9:58 am

Coming back to this several years after my original post, I notice that

a) the "gold hold" is now much shorter than it used to be, which will help with my original issue of too much combined heatwork when tack fusing gold-bearing glass &

b) whereas in my first kiln I always had a bubble squeeze (pre-rapid heat soak) at 627C and then added in the gold hold after that & before going up to fusing temperature, my new kiln suggests a bubble squeeze at 677C for Bullseye glass. So I guess that the 45 minute hold at 663C can do both jobs at once, & it hopefully won't do any harm to hold for longer at 663C if I need a longer bubble squeeze?

But: if, for example, I need a 2 hour bubble squeeze, can I do this at 663C or will that cause the gold molecules to clump together & cause the sapphirine (I think it's called?) effect, where the gold bearing glass then looks brown in reflected light but still pink or purple in transmitted light?
mattt
 
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