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kiln question

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kiln question

Postby faith » Mon Mar 08, 2010 9:26 am

I am new to fusing glass and am having difficulty in getting the glass to fully fuse. If this happens is it better to raise the working temp. or the hold time? I am doing fairly small pieces, nothing bigger than 7 inches in diameter, about 1/4 inch thickness in most cases. Thanks in adavance for any suggestions.
faith
 

Re: kiln question

Postby marykaynitchie » Mon Mar 08, 2010 9:28 am

Hi Faith,

What is your current process temperature and hold time?

Mary Kay
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Re: kiln question

Postby faith » Mon Mar 08, 2010 9:31 am

Hi Mary Kay -- 180 dph to 1000 for 15 min. -- full to 1470 for 15, full to 960 for 2 hours and then cool 240 dph to 700 for 25 min. and off. I should say that this was casting two small earring molds holding small chunks of frit.
faith
 

Re: kiln question

Postby marykaynitchie » Mon Mar 08, 2010 9:52 am

Hi Faith,

I am assuming that you are using Bullseye glass. You could try changing one variable at a time, but I suspect you could change a few to more successful results.

Test 1:
Try holding at 1250 degrees F instead of 1000. This might be the only change you need because at 1000 the glass is not really softening at all. I would try that first, and keep the process temperature at 1470.

Also, you can shorten the annealing time to 30 minutes instead of two hours. This won't make any difference in how much your glass fuses, and your pieces are small enough that they can be successful with a shorter annealing cycle.

Test 2:
If Test 1 doesn't work, then keep the changes you made in Test 1, but raise the process temperature to 1500.

Let us know what happens!

Mary Kay
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Re: kiln question

Postby faith » Mon Mar 08, 2010 10:13 am

Thank you so much Mary Kay, I will give it a try.
faith
 

Re: kiln question

Postby andeehunt » Tue Mar 16, 2010 9:55 pm

A friend of mine had a very similar query which faith's had. I was indeed looking for some suitable suggestion. I asked my friend to implement it and it really worked. A loads of thanks to you Mary.
andeehunt
 

Re: kiln question

Postby marykaynitchie » Wed Mar 17, 2010 11:00 am

Andee,

You've made my day! I love finding out that a suggested method works for someone.

Happy St. Patrick's Day!

Mary Kay
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Re: kiln question

Postby Suzanne Chudnoff » Sun Mar 21, 2010 1:47 pm

Mary Kay, you wrote back to hold the glass at 1200 degrees. Isn't this in the devit range? I went to a class given by Boyde Lundstrom a few months ago, and asked him specifically about the devit range. He said that from all his experience he's found that range to be anywhere from 1175-1300. It seems like everyone has there own theory, but we still continue to get devit. What exactly is Bullseye's position. Every book states a different temperature range.

Suzanne
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Re: kiln question

Postby bertglass » Sun Mar 21, 2010 3:01 pm

Suzanne

Proneness to devit is caused by uncleanliness and by glass compostion formulas. Bullseye glasses have been reformulated over the years to be less devit prone. Some opals can still be problematic.

In the olden days we were told to speed through the devit zone, up and down. This caused many more problems than it solved. Today the general approach is slow heating to lower temperatures and hold longer.

If you are having problems look first to what kind of glass cleaner you are using. Windex will cause scum. If you are not having problems, don't belabour solving them. I've noticed that people who follow the old myths have many more problems than those who don't.
Bert Weiss
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Re: kiln question

Postby marykaynitchie » Mon Mar 22, 2010 9:07 am

Hi Suzanne,

Our "exact position" on many kilnforming matters may change over time, as we have full-time kilnforming researchers on staff exploring new questions, and re-examining old assumptions. I understand there is a lot of conflicting information out there about kilnforming methods. You are correct to question your information sources, and consider who has the most accurate and useful information for your particular application of the materials.

Our current position on the devitrification range is covered in TechNotes 4: Heat and Glass. The latest version is always downloadable from our website. http://www.bullseyeglass.com/education/

However, as Bert noted, the temperature is just one of many variables that likely combine to provoke devitrification. Glass chemistry, cleaning methods, and over-insulation of kilns (which can lengthen the time spent in the devit range) all can contribute to devitrification. If you want to understand what might be causing devitrification in your own work, feel free to start a new thread on the Forum, be ready to provide lots of details on your materials and methods, and Forum members and techs will help you investigate this.

Mary Kay
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