a thousand questions....

[shardsman]

HI! I am new to warm glass and have been making enough mistakes now for the last 4 months to now ask intelligent questions..
I bought 2 books, one was Warm Glass...worth only about 1/10th of what I paid for it. I was told it would answer all my questions..
So I will start off with just a few random questions from the top of my current list of 20..

1. Can kiln wash be reused after it has dried in the mixing dish?

2. how far should the thermocouple intrude into the kiln?

3. Can glass stay over 1500F too long?

4. what are the major causes of devitrification?:frustrated:

5. what is the lowest temp to open the kiln and not have any thermal shock?

so that's it for this time around...
thanks!
Jim

[bert weiss]

Answers are in red.

HI! I am new to warm glass and have been making enough mistakes now for the last 4 months to now ask intelligent questions..
I bought 2 books, one was Warm Glass...worth only about 1/10th of what I paid for it. I was told it would answer all my questions..
So I will start off with just a few random questions from the top of my current list of 20..

1. Can kiln wash be reused after it has dried in the mixing dish?Yes

2. how far should the thermocouple intrude into the kiln?
a few inches

3. Can glass stay over 1500F too long?
There isn't a simple answer to this. My firing strategies are to go low and slow. I rarely find a reason to go above 1500. I don't comb or do potmelts. Above 1500ºF, you risk COE shifts.

4. what are the major causes of devitrification?:frustrated:
dirt or grease is the major cause. Cleanliness is the most important factor. In the olden days people went to great machinations to go quickly above 1400. I find that simply cleanliness is required. I go very slow in the hot zones

5. what is the lowest temp to open the kiln and not have any thermal shock?
My general rule is that I can crack the kiln open a bit at 300 and I never remove glass unless it is cool enough to do so with my bare hands. A good rule of thumb is that the more work and money you have invested in a piece, the more conservative you should be at the bottom of the schedule. Thick multicolored pieces are more vulnerable to cold shock, than simple single color glass.

so that's it for this time around...
thanks!
Jim

[Dennis Brady]

1. Can kiln wash be reused after it has dried in the mixing dish?
You might find it more convenient to use a bottle instead of a dish. Take an empty drink bottle and with a spoon put in enough KW to about 1/6th of the way up. Then fill to the top with water. Whenever you want to use the KW, just vigorously shake the bottle then pour some out into a shallow bowl or ashtray. No need to pour out a lot. Just enough for what you're now applying. When you leave the bottle sitting, the KW will settle to the bottom. No problem - just shake it up again.


2. how far should the thermocouple intrude into the kiln?
About 1" to 1.5" is sufficient. Too little and it won't read accurately. Too much and it's in the way loading and unloading. I have several kilns in which I replaced thermocouples and all perform perfectly set in 1".

3. Can glass stay over 1500F too long?
I'm sure it's possible to stay too long but that would be a very considerable time. I routinely do melts at 1700F with over an hour hold and drip casts at 1800 for several hours. I believe it depends more on the glass then the time.

4. what are the major causes of devitrification?
My experience has been that some glass is especially susceptible to it while others almost impervious. Major causes are contamination and firing too slow through the temperature range most likely to induce devit. That's why firing schedules almost always call for a drop temperature as fast as possible from top down to anneal.

5. what is the lowest temp to open the kiln and not have any thermal shock?
Depends on size. For small jewelry pieces we often open at 500. Otherwise, the practice is 3-2-1. At 300F crack the lid an inch or two, at 200F fully open the lid, at 100F remove and reload. This is our standard shop practice on all firings up to 3/4" thick. For thicker firings, we assume the glass temperature is at least 50 deg F hotter then then thermocouple is reading. Regardless of temperature, all thick firings are wrapped in towels or blankets immediately after leaving the kiln and left for several hours.

More questions? There's a quantity of material here you'll find helpful. I especially recommend Kilnforming Kindergarten.
http://www.glasscampus.com/tutorials.htm

[Rebecca Lee]

I lean more towards Bert's method of firing, low and slow. Unless you're working with a technique that absolutely needs high temps there's really no reason to go there.

Read everything you can get your hands on and ask questions when you have them! While Dennis's site may have some great information it's still one man's method of doing things! Learn from the different sites and discussion boards and experiment. Find what works for you. Also check out the Bullseye and System 96 sites. There is so much information out there!

Good luck and have fun!