Go and stop and go? Or just go? - WarmGlass.com

Go and stop and go? Or just go?

This is the main board for discussing general techniques, tools, and processes for fusing, slumping, and related kiln-forming activities.

Moderators: Tony Smith, Brad Walker

Post Reply
Brad Walker
Site Admin
Posts: 1363
Joined: Fri Mar 07, 2003 9:33 pm
Location: North Carolina, USA
Contact:

Go and stop and go? Or just go?

Postby Brad Walker » Wed May 30, 2012 8:12 pm

I've noticed that many of the firing schedules that are in the canned programs, as well as some published schedules (such as the slumping schedule recommended by System 96), call for a ten to fifteen minute hold on the way up through the initial heating range. Usually the hold is around 500F, but can be as low as 300F or even multiple holds every few hundred degrees.

I've always thought this was unnecessary, arguing that if the rate was slow enough, no hold is needed during the initial firing phase. And, as a matter of practice, just about the only time I throw a hold in (usually around 500F) is when I know I'm pushing the limits on firing and I'm gambling that a ten minute hold will help me fire quicker than I know I ought to. But those situations are infrequent; I much prefer to avoid these secondary holds.

But I'm wondering -- do others hold on the way up during the initial heating phase? If so, why and at what temperatures? And anyone have any guesses on why so many of the canned programs insert this hold as a matter of routine?

The Hobbyist
Posts: 303
Joined: Sun Mar 09, 2003 7:09 pm
Location: Sun City West (NW Phoenix), AZ
Contact:

Re: Go and stop and go? Or just go?

Postby The Hobbyist » Wed May 30, 2012 8:47 pm

Excluding a bubble squeeze schedule I don't put in a hold on the way up. If I'm concerned with thermal shock because of thickness, nearness to the elements or complexity of the piece I simply slow down.

Jim
"With or without religion, good people can behave well and bad people can do evil; but for good people to do evil—that takes religion. " Steven Weinberg

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Re: Go and stop and go? Or just go?

Postby Brock » Wed May 30, 2012 8:56 pm

Ditto. No holds. Adjust your schedule for thickness, but it's a continuous curve . . .

Bert Weiss
Posts: 2338
Joined: Tue Mar 11, 2003 12:06 am
Location: Chatham NH
Contact:

Re: Go and stop and go? Or just go?

Postby Bert Weiss » Wed May 30, 2012 9:19 pm

Heating up to the strain point has but one challenge: don't crack the glass. I see no reason for a hold, you have to go at a rate that will work. The first place you need a hold is the bubble squeeze. This takes some time to accomplish when the glass is soft enough to move, but not soft enough to stick and seal the bubbles in. The rest of the heatup schedule is designed to finish the heatwork.

Personally I shut off power and naturally cool to anneal soak. I soak low and long. I have read arguments here for stopping and soaking higher. I can not say they are right or wrong. I don't find this step necessary when annealing sheets of float glass. Up until Bullseye published their heavy anneal schedules, all the published schedules I read, stopped a bit hot, for a relatively short soak, followed by a slow ramp through the strain point. I have always annealed in the recently updated Bullseye style of holding at a lower temperature for a longer time. Once below the strain point, you can go quicker for the next 200ºF, and then quicker down to room temp. All the kilns I know, cool slower than the glass is capable from around 600 or 700ºF, down to room temp, unless you are firing quite thick and slowly.

Recently I have been fusing broken tempered float glass. This glass behaves quite differently from my usual sheet glass. It requires more heat to fuse, I anneal it for about 1/4" thicker than the glass actually is, and it requires a very slow reheat schedule. I suppose this is closer to tack fusing multiple compatible glasses.

Cooling investment castings is a different challenge than cooling sheets of glass on a shelf. That task is more complex as you have movements taking place in both the glass and the investment. There are strategies to avoid suckies (gaps in the casting)

I am totally clueless how most people devise their firing schedules. They usually make no sense to me. Often people will send me a picture of broken glass along with a firing schedule. The schedules are almost always incomprehensible to me. The strange thing to me is that on the Bullseye tech ed site, they give some pretty good info. People are not even close to doing it their way though. Like Brad said, holds at odd points, very high anneal soak points, etc. My understanding is that Bullseye and System 96 can use the same anneal schedules. They do have different heatwork needs as 96 is softer and has higher expansion and contraction.

I no longer have my copy of Fusing Book One. Back in the late 80's I did slump tests to determine anneal soak temps. My results told me to soak float at 1000ºF, and Bullseye and Spectrum at 920ºF. (a short soak at 960 and a long ramp to 820 yields about the same result) The thicker the glass gets, Bullseye now recommends lowering the soak temp.

I do wish I understood why there are so many really bad firing schedules floating around.
Bert

Bert Weiss Art Glass*
http://www.customartglass.com
Furniture Lighting Sculpture Tableware
Architectural Commissions

Brad Walker
Site Admin
Posts: 1363
Joined: Fri Mar 07, 2003 9:33 pm
Location: North Carolina, USA
Contact:

Re: Go and stop and go? Or just go?

Postby Brad Walker » Wed May 30, 2012 9:53 pm

Bert Weiss wrote:I am totally clueless how most people devise their firing schedules. They usually make no sense to me. Often people will send me a picture of broken glass along with a firing schedule. The schedules are almost always incomprehensible to me.


That's kind of why I started this thread. I don't understand why almost all of the canned schedules have weird holds on the way up, nor why System 96 advocates a hold at 300F on the way up for a slump (but not for a fuse). (Not talking about bubble soak, either, just holds before 1000 or 1100 on the way up.)

My understanding is that Bullseye and System 96 can use the same anneal schedules.


Don't know why not, either. After all, the annealing temp is an AVERAGE of a bunch of different glasses, and a particular temp in my kiln is not the same as the same temp in yours. For most basic fuses and slumps, just be somewhere in the neighborhood of 900 to 960F. (Thicker items are a different issue; BE's lower hold time saves time on long anneals -- but that ought to work for System 96, too.)

Don Burt
Posts: 537
Joined: Sun Mar 09, 2003 8:45 pm
Location: Cincinnati, Ohio
Contact:

Re: Go and stop and go? Or just go?

Postby Don Burt » Thu May 31, 2012 7:33 am

I'd guess that the hold on the up ramp is some sort 'organic burn out' phase. Like holding at 300°F will burn glue out and let the fumes dissipate before advancing to temperatures above 300°F, where it is unstylish and poor form to have such fumes remain in the kiln. Or perhaps Spectrum knows about an expansion characteristic of some of their glasses where there the curve is elevated in slope just above 300°F, so holding at 300°F, letting all kiln components and glass reach 300 evenivity before advancing to the dangerous 300+ part of the curve, is a canny practice. If my pieces seemed to break a lot at 300°F-400°F on the up ramp, I could see how a hold at 300°F could add effectiveness to what presumably would be a slower ramp following the initial <300 ramp, more economically than simply slowing down the entire approach. Maybe. Well, possibly.

rosanna gusler
Posts: 730
Joined: Mon Mar 10, 2003 2:22 pm
Location: wanchese north carolina
Contact:

Re: Go and stop and go? Or just go?

Postby rosanna gusler » Thu May 31, 2012 9:51 am

organics burn out between f451 and 1000f ish. i always hold at 1100f ish for evenivinity sake. everything just goes better if i hold there for at least 20 min to an hour. rosanna
artist, owner of wanchese art studio, marine finisher

Brad Walker
Site Admin
Posts: 1363
Joined: Fri Mar 07, 2003 9:33 pm
Location: North Carolina, USA
Contact:

Re: Go and stop and go? Or just go?

Postby Brad Walker » Thu May 31, 2012 10:15 am

rosanna gusler wrote:organics burn out between f451 and 1000f ish. i always hold at 1100f ish for evenivinity sake. everything just goes better if i hold there for at least 20 min to an hour. rosanna


Agree with this. But I don't understand the need to hold at 300F or 500F or anywhere else on the way up. I was hoping someone who used that schedule had some light to shed on the logic behind it. For example, I'm not buying that two layers of Spectrum System 96 glass needs to be fired at 150dph to 300F, held 15 minutes, then fired at 300dph to 1100F before holding again. (That's the recommended schedule at system96.com) In my experience the dangerous part of the thermal shock curve is closer to 500F than 300F and besides, 300dph with no hold has always worked fine in my firings of S96 and BE. The issue is definitely not organics such as glue, almost all of which burn out much higher than 300F.

By the way, I really miss Brian Blanthorn -- "eveninity" is one of the greatest words ever invented.

Kevin Midgley
Posts: 713
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: Go and stop and go? Or just go?

Postby Kevin Midgley » Thu May 31, 2012 10:22 am

How many kilns really evenly heat?
How many kilns are overpowered?
That is the answer.

Bert Weiss
Posts: 2338
Joined: Tue Mar 11, 2003 12:06 am
Location: Chatham NH
Contact:

Re: Go and stop and go? Or just go?

Postby Bert Weiss » Thu May 31, 2012 10:27 am

rosanna gusler wrote:organics burn out between f451 and 1000f ish. i always hold at 1100f ish for evenivinity sake. everything just goes better if i hold there for at least 20 min to an hour. rosanna
The goal up to the strain point is to not break. Above the strain point it is all about heatwork. In the 80's, Fusing Book One suggested you fire AFAP up to top temp and crash cool. Since then, fusing glasses were reformulated to be less prone to devit (96 didn't even exist then). We know from practice that going slower gets the heatwork done better with fewer catastrophes, like bubble blowouts. One of the big ridiculous schedule sources are people who never changed strategy from 1983.

As far as organic burnout goes, if you are using enough organics in the kiln to cause problems, you either need to vent them, or think twice about why you need these. (there are some reasonable uses).

I won't argue with people who stop for a soak on the way down to anneal soak. They claim good results, with which there is no reason to dispute. What is important to understand is that this is not an anneal soak, just an equalizing step before annealing.

Annealing is a ridiculously simple event. You need to get 100% of the glass within 5ºC, inside the annealing range, for 15 seconds. Annealing actually happens faster and easier at the lower end of the range than the upper end. Once relaxed you have to go slowly through the strain point, and then the pace can speed up somewhat, followed by a relatively quick pace down to room temp. The catch is that a quick gust of cold on a hot piece of glass will cause thermal shock.

One of these days, I would love to do the exercise of embedding thermocouples in the center, top, and bottom of some glass and recording how the glass changes relative to the air temperature. This test will teach you an awful lot about why firing schedules are the way they are. You can get some very thin thermocouples for this.
Bert



Bert Weiss Art Glass*

http://www.customartglass.com

Furniture Lighting Sculpture Tableware

Architectural Commissions

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Re: Go and stop and go? Or just go?

Postby Brock » Thu May 31, 2012 10:30 am

I believe these complicated schedules with pointless holds exist because you can just program them.
Before controllers we never used schedules like these. People who know what they are doing don't use them.

Bert Weiss
Posts: 2338
Joined: Tue Mar 11, 2003 12:06 am
Location: Chatham NH
Contact:

Re: Go and stop and go? Or just go?

Postby Bert Weiss » Thu May 31, 2012 10:47 am

Brock wrote:I believe these complicated schedules with pointless holds exist because you can just program them.
Before controllers we never used schedules like these. People who know what they are doing don't use them.
I was shocked when I visited some factories in Murano and all their annealing was done in a garage. This is a fire brick box sitting around 900ºF. After work each day, the heat was shut off and the garage cooled on it's own, over night.
Bert



Bert Weiss Art Glass*

http://www.customartglass.com

Furniture Lighting Sculpture Tableware

Architectural Commissions

DonMcClennen
Posts: 370
Joined: Sun Mar 09, 2003 9:09 pm
Location: Ontario

Re: Go and stop and go? Or just go?

Postby DonMcClennen » Thu May 31, 2012 12:46 pm

I recall Boyd Lundstrums (sp?) second book "Advanced Fusing" recomends holding and or changing rates at 300F for some reason, ..also he talked about letting heating of mold catch up to heating of glass.........I'm removed from my library right now or I would check.
"The Glassman"

Kevin Midgley
Posts: 713
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: Go and stop and go? Or just go?

Postby Kevin Midgley » Thu May 31, 2012 1:52 pm

Don, see my above post.
Brian's Evenivity said it all.
The average kiln is not going to heat the contents evenly.

Jerrwel
Posts: 129
Joined: Thu Feb 10, 2005 6:25 pm
Location: Charlotte, NC

Re: Go and stop and go? Or just go?

Postby Jerrwel » Sun Jun 03, 2012 1:31 pm

As always, I'm consulting Graham Stone's Firing Schedules for Glass/The Kiln Companion and find his discussion on pages 98-99 of a 'Catch-up Schedule' where the schedule has holds at F250 and F500 in the heating phase. He specifies that the schedule is designed to compensate as suggested earlier in this thread for eveninity or uneven heating which may exist in a given project either knowingly or unknowingly by the fuser.

So I'd suggest that the 'canned' schedules have the holds to compensate for stress-inducing situations which may be introduced by the novice or schedule-challenged fuser to allow them greater success in their efforts. This is a good self-preservation/marketing move so that the fuser is more successful and buys more glass, kilns and other supplies while remaining unaware of their scheduling issues. My supposition then is that manufacturers and instructors (if indeed overtly aware of the issue) provide excessively conservative schedules to enhance the success of those less experienced or trained in the practice of fusing than the respected experts on this site.

Once introduced as a practice, the holds could remain in experienced fusers' schedules just 'cause it works.
Jerry

Bert Weiss
Posts: 2338
Joined: Tue Mar 11, 2003 12:06 am
Location: Chatham NH
Contact:

Re: Go and stop and go? Or just go?

Postby Bert Weiss » Sun Jun 03, 2012 3:28 pm

Jerrwel wrote:
Once introduced as a practice, the holds could remain in experienced fusers' schedules just 'cause it works.
The holds are not in my practice because it works without them. Including them would, in my estimation, be a waste of time. It would still work though.

I like Stone. But, there is always more than one way to accomplish all of our goals, both heating and cooling. I had figured out my own annealing schedules based on advice from an engineer from PPG research along with Lundstrom. My schedules have always worked for me. When I got Stone, I saw that we were spending about the same time frames, but I was soaking longer at a lower temp and then ramping down. When I asked the experts which approach was better, I was told mine was. Believe me this was a total surprise to me. Several years later those same experts adjusted all the Bullseye thick anneal schedules to reflect that line of thinking.

On one hand, there is always more than one way to get the jobs done. On the other hand, if you program wrong, you can fail miserably. For instance, you will not be annealing Bullseye with a long soak at 990.
Bert



Bert Weiss Art Glass*

http://www.customartglass.com

Furniture Lighting Sculpture Tableware

Architectural Commissions

Wallace Venable
Posts: 38
Joined: Sun Mar 09, 2003 8:34 pm
Location: Morgantown, WEST Virginia
Contact:

Re: Go and stop and go? Or just go?

Postby Wallace Venable » Sun Jun 03, 2012 6:20 pm

I would guess that these schedules are artifacts of an "ancient" way of doing glass fusing.

Before the introduction of computers and digital controllers, how would you do a ramp? Probably by turning the temperature knob on your kiln in a number of steps.

For example, a schedule might say "Set knob to Mark 1 and hold for 20 minutes, turn knob to Mark 2 and hold for 25 minutes," etc.

Since your kilns were different from those owned by you friends, and your kilns differed, It was better to say "400 degrees" than "Mark 1." Then each schedule could apply to many kilns.

Following that, there was a stage when ramping was done in some cases with clock motors which turned the temperature knob at a slow rate.
Wally Venable, Student of glass

Morganica
Posts: 1079
Joined: Mon May 19, 2003 6:19 pm
Location: Portland, OR
Contact:

Re: Go and stop and go? Or just go?

Postby Morganica » Mon Jun 04, 2012 2:16 pm

Depends on what I'm doing. I almost never hold before 1100F when fusing. In casting, I will program one or more holds on the way up, one between 240-300F to eliminate water in the mold (and that one can last for 24 hours or more), another around 700-800F to burn out organics, if I'm re-casting against an organic wax filler.

I'd agree, many people just expand their firing schedule to match the number of available segments in the controller, but I don't suppose it hurts anything. I prefer defining what the glass ought to be doing at each stage, and building a program around those requirements.

I've been told by various instructor types that the holds in a fusing program on the way up are for maintaining temperature in a cheap, underinsulated kiln, so that you can season any new molds and/or burn out glue and price stickers and such on the glass, and/or to eliminate water in kilnwash and prevent it from fogging the glass. I think it wastes time and electricity but if it provides a measure of comfort until people figure that out, hey...
Cynthia Morgan
Marketeer, Webbist, Glassist
http://www.morganica.com/bloggery
http://www.cynthiamorgan.com

"I wrote, therefore I was." (me)

jim simmons
Posts: 463
Joined: Sun Mar 09, 2003 10:37 pm
Location: Hillsboro Oregon
Contact:

Re: Go and stop and go? Or just go?

Postby jim simmons » Tue Jun 05, 2012 7:39 pm

Same here
The "other Jim"


The Hobbyist wrote:Excluding a bubble squeeze schedule I don't put in a hold on the way up. If I'm concerned with thermal shock because of thickness, nearness to the elements or complexity of the piece I simply slow down.

Jim

Havi
Posts: 594
Joined: Wed Jul 02, 2003 6:01 am
Location: Israel
Contact:

Re: Go and stop and go? Or just go?

Postby Havi » Wed Jun 06, 2012 4:22 am

jim simmons wrote:Same here
The "other Jim"


The Hobbyist wrote:Excluding a bubble squeeze schedule I don't put in a hold on the way up. If I'm concerned with thermal shock because of thickness, nearness to the elements or complexity of the piece I simply slow down.

Jim


SAme here too....................

However, if I remember correctly, Graham Stone devides the firing process so, that at 250 centigrade he makes a pause. He explains that up to this temp. the glass is extremely fragile, up to 530 very fragile - and then one can work a bit quicker. My poor memory's 2 penny

Havi
Haviva Z
- - - - with a smile :)

"Speed comes from the Devil" - (an Arabic proverb)
Image
http://www.havivaz.com


Post Reply

Return to “Techniques and Tools”

Who is online

Users browsing this forum: Google [Bot] and 39 guests

Warm Glass

2575 Old Glory Road, Suite 700
Suite 700
Clemmons, NC 27012
Phone: (336) 712 8003
Email: wg@warmglass.com

cron