fastest - but safe - annealing for float 2 layers

[seachange]

Hi,

Could you please recommend the fastest (while still safe) annealing schedule for 2 layers of float (total thickness 1/4")? Pieces are smallish, 4" and 5" square plates

I am very much behind with the work for the season, starting to panic, so trying to make 2 firings in one day, in the same kiln.

Thinking that if I can get a fast annealing - without risking the pieces - the kiln will cool faster and I can do my second firing in the afternoon.

Kiln is a large Evenheat, brick, coffin shape, with elements on the lid and the sides.

Many thanks for any suggestions.

Best regards, seachange

[De Anza Art Glass Club]

I have some old tapes from Dragon Glass and here is what they recommend:
Annealing schedule
Size - from 30cm (12") to 45cm (18")
Total thickness of glass 3mm (1/8") - 6mm (1/4")
Fire down from 650C/1200F no faster than 150C/300F

Glass Notes by Henry Halem says 1 hour at annealing temperature, then another 1.25 hours to cool from annealing temperature (1/4" or 0.635 cm glass) at the rates 400F/hr (222C/hr) for the first 200F (111C) from annealing temperature, 500F/hr (335C/hr) for the next 100F (55C), 333F/hr (165C/hr) for the next 100F(55C), and 600F/hr (333C/hr) for the next 150F (83C) for a total of 2.25 hours for annealing and cool down.
However, this annealing schedule is for open shapes (cooling on two sides).
For other shapes, the book seems to defer to the Bullseye schedules, which call for a 1 hour soak, then a maximum cooling rate of 100F/hr (56C/hr) to 700F (371C) and then as fast as possible to room temperature.

[seachange]

I have some old tapes from Dragon Glass and here is what they recommend:
Annealing schedule
Size - from 30cm (12") to 45cm (18")
Total thickness of glass 3mm (1/8") - 6mm (1/4")
Fire down from 650C/1200F no faster than 150C/300F

Glass Notes by Henry Halem says 1 hour at annealing temperature, then another 1.25 hours to cool from annealing temperature (1/4" or 0.635 cm glass) at the rates 400F/hr (222C/hr) for the first 200F (111C) from annealing temperature, 500F/hr (335C/hr) for the next 100F (55C), 333F/hr (165C/hr) for the next 100F(55C), and 600F/hr (333C/hr) for the next 150F (83C) for a total of 2.25 hours for annealing and cool down.
However, this annealing schedule is for open shapes (cooling on two sides).
For other shapes, the book seems to defer to the Bullseye schedules, which call for a 1 hour soak, then a maximum cooling rate of 100F/hr (56C/hr) to 700F (371C) and then as fast as possible to room temperature.

Many thanks for your reply (and for the translation into C ), it does not look like one can save much time at this critical phase...I am glad my plates are small

Will keep this very useful information handy.

Best regards, seachange

[williamslaybaugh]

Without knowing the details of your pieces other than size and your currant firing schedule. I would think that the thermal mass of your kiln is slowing you down more than your annealing hold time. With only two layers of glass I would shut the kiln off when the pieces were done and let the kiln cool on its own. I still don't think your going to get a second firing in by afternoon with that type of kiln though. The only way I can get two firings in one day from a small 110v brick kiln is setting enamels on one layer going to 1250F with no hold. It takes about four hours to cool. I prop it open at 500F and I open it full at 200F for up to a 9in square. I would say if you're looking for a faster turn around time lower your thermal mass and go with a fiber kiln.

[seachange]

Without knowing the details of your pieces other than size and your currant firing schedule. I would think that the thermal mass of your kiln is slowing you down more than your annealing hold time. With only two layers of glass I would shut the kiln off when the pieces were done and let the kiln cool on its own. I still don't think your going to get a second firing in by afternoon with that type of kiln though. The only way I can get two firings in one day from a small 110v brick kiln is setting enamels on one layer going to 1250F with no hold. It takes about four hours to cool. I prop it open at 500F and I open it full at 200F for up to a 9in square. I would say if you're looking for a faster turn around time lower your thermal mass and go with a fiber kiln.

Thermal mass is certainly one of the problems. My idea was to put the kiln on the delay timer, so that the firing starts at early dawn and is practically ready when I get up (I crashcool float to get it quickly out of devit range). Any time saved in the annealing process (stepped cool downs and holds) would help to get the kiln cool enough for the next lot, hopefully by around 2 to 3 pm, even if it is just for slumping, which is a shorter firing.

Have tested the natural cool down, but I think it is a bit too fast to ensure pieces won't crack at a later date, when in the customer's hands...it is practically impossible to test this, so rather be safe. It does work well for smaller pieces though, up to pendant size.

Have thought about fiber kilns, but it remains just a thought. Haven't got the space for another large kiln, plus here in Australia they are extremely expensive.

Perhaps one day my husband will build one - and the shed to go with it

Many thanks for your help, I appreciate it.

Best regards, seachange

[Bert Weiss]

I anneal 6mm float glass like this:

Hold at 1000ºF for 36 minutes
1000 > 900 take 36 minutes
900 > 700 take 24 minutes
700 > 300 take 24 minutes

Hold at 540ºC for 36 minutes
540 > 480 take 36 minutes
480> 370 take 24 minutes
370 > 150 take 24 minutes

[seachange]

I anneal 6mm float glass like this:

Hold at 1000ºF for 36 minutes
1000 > 900 take 36 minutes
900 > 700 take 24 minutes
700 > 300 take 24 minutes

Hold at 540ºC for 36 minutes
540 > 480 take 36 minutes
480> 370 take 24 minutes
370 > 150 take 24 minutes

Thanks Bert

Would you consider this as very conservative for 4x4" and 5x5", or it is what I have to do to be safe, independent of being in a hurry?

Have been annealing with the same first two steps (only difference is 30 minutes instead of 36 at 540C), then kiln off after reaching 480. Probably similar step down temperatures as you in the end, because I have a brick kiln and yours is fiber.

Many thanks and best wishes, seachange

[charlie]

the smaller it is, the less important annealing is. for magless's, you don't have to anneal at all.

[Bert Weiss]

I use the same annealing schedule for 4" x 4" x 6mm or 40" x 80" x 6mm. Charlie is right 1" x 1" is easier to anneal. According to the formula I use for determining annealing schedules, my schedule is quite conservative.

[seachange]

I use the same annealing schedule for 4" x 4" x 6mm or 40" x 80" x 6mm. Charlie is right 1" x 1" is easier to anneal. According to the formula I use for determining annealing schedules, my schedule is quite conservative.

Thanks Bert, remembered from previous posts you mentioning that your annealing schedules are conservative.

Because of the size of my pieces, I'll probably be safe if I reduce hold time a bit.

Thanks Charlie also, you are very right with the 1x1", never had any break without annealing. For 4x4, well, I better put a bit of time in to ensure survival

All best wishes, seachange

[Bert Weiss]

I worry about spending too much time in anneal cycles. There used to be a notion that this is impossible. However, think about it. If your kiln has uneven temperatures in it, the longer you hold your glass in an uneven place, the more it will resemble that space. If that difference is greater than 5ºC, it is impossible to actually anneal. If you don't stay there too long, this won't become a problem. The 2 places most likely to be different are the edges near the kiln walls, and the center furthest from the walls. Of course the larger your piece of glass, the more likely you encounter such problems.

[seachange]

I worry about spending too much time in anneal cycles. There used to be a notion that this is impossible. However, think about it. If your kiln has uneven temperatures in it, the longer you hold your glass in an uneven place, the more it will resemble that space. If that difference is greater than 5ºC, it is impossible to actually anneal. If you don't stay there too long, this won't become a problem. The 2 places most likely to be different are the edges near the kiln walls, and the center furthest from the walls. Of course the larger your piece of glass, the more likely you encounter such problems.

Although I don't know much about the subject of annealing, what you say makes sense to me.

Intuitively I divide my coffin type kiln mentally into 3 sections. I picture the center section as a bit bigger, and this is where I place all the larger pieces that need more care with the annealing, so the right and left sides are away from the walls.

However, if I fuse 4x 10x10" plates in this area, the top edge of two of the plates, and the bottom edge of the other 2 plates are going to be about 3'' away from the front and back walls. I place the shelves so that the edges are facing the bricks, above the coils.

For this reason, in this case I anneal conservatively, following your suggestion, without trying to skimp on the time (both when fusing the blank and when slumping). However, have only started making these recently...hopefully I am doing a good job and they won't explode in the future

I very much appreciate your help.

All best wishes, seachange

[Jerrwel]

I place the shelves so that the edges are facing the bricks, above the coils.
...hopefully I am doing a good job and they won't explode in the future

This thread is taking some interesting turns in topic. Seachange introduces two topics here that lead to an additional comment and a couple of questions:

Since volume production is the initial issue, can she merely add shelves to what is probably a 13” deep kiln to double or possibly triple the kiln capacity; especially on initial blank firing? Brad had a picture of Brock's kiln with many shelves in the first edition of his book; what are the guidelines for placement of multiple shelves as far as distance between shelves and relation to coils? I recall reading somewhere (?) that the side coils should be between the shelves versus at the same level as the shelves; is that so? Also seem to remember one reliable contributor here writing that 1" was minimum space required between product and coil (?).

Really, really appreciate that Seachange is concerned about the durability of her products. Are there ways to test her products/designs? Some thoughts....
* Even if a product is not going to be transparent, create a transparent test piece of the same design so that polarized film can be used to inspect for stress in the basic design? (edit - oops, forgot that float glass is being used but I'll leave my question as written)
* Subject the product or test pieces to heat/cold to induce stress and test durability?
* Tap product with a hammer to induce stress and test durability?

Greatly appreciate others' thoughts.

[Bert Weiss]

I think 3" from the kiln walls is sufficient. I have seen people do 1/4", which I do not think is sufficient.

[seachange]

I think 3" from the kiln walls is sufficient. I have seen people do 1/4", which I do not think is sufficient.

Great, thanks Bert!

Best regards, seachange

[seachange]

I place the shelves so that the edges are facing the bricks, above the coils.
...hopefully I am doing a good job and they won't explode in the future

This thread is taking some interesting turns in topic. Seachange introduces two topics here that lead to an additional comment and a couple of questions:

Since volume production is the initial issue, can she merely add shelves to what is probably a 13” deep kiln to double or possibly triple the kiln capacity; especially on initial blank firing? Brad had a picture of Brock's kiln with many shelves in the first edition of his book; what are the guidelines for placement of multiple shelves as far as distance between shelves and relation to coils? I recall reading somewhere (?) that the side coils should be between the shelves versus at the same level as the shelves; is that so? Also seem to remember one reliable contributor here writing that 1" was minimum space required between product and coil (?).
Greatly appreciate others' thoughts.

Hi Jerry,

The kiln is an Evenheat, oval GTS 2541. The elements in the lid consume 7Kw of power, or 73% of the total power. The coil on the side walls (one coil, making 2 turns around the walls, placed on the bottom half of the walls) consume only 2.6 Kw, or 27%.

I don't think in this type of kiln stacking shelves would be workable.

One thing that does work is to place smaller items on small shelves on the left and right sections of the kiln. Although these sections are a bit cooler, by elevating the small side shelves and bringing them closer to the lid elements, results tend to be similar to those in the center section of the kiln.

However haven't made tests as yet with exactly same size items (let's say 4x4" in the center plus on elevated shelves on each side), to compare exactly. Seem to always have enough small things to fill the side shelves (pendant size).

Eventually I will need to find out.

All best wishes, seachange

[Jerrwel]

I don't think in this type of kiln stacking shelves would be workable.

The manufacturer's website gives the following limitation:

' It should be noted that the GTS 2541 is designed to fire a single layer or shelf. The nature of the GTS 2541 is to provide heat from the lid elements directly to the shelf containing the glass. Attempting to fire glass below the top shelf is likely to lead to frustration and disappointment.'

[seachange]

I don't think in this type of kiln stacking shelves would be workable.

The manufacturer's website gives the following limitation:

' It should be noted that the GTS 2541 is designed to fire a single layer or shelf. The nature of the GTS 2541 is to provide heat from the lid elements directly to the shelf containing the glass. Attempting to fire glass below the top shelf is likely to lead to frustration and disappointment.'

Well, exactly my thoughts

Cheers, seachange

[Jerrwel]

Hi,
Could you please recommend the fastest (while still safe) annealing schedule for 2 layers of float
trying to make 2 firings in one day, in the same kiln.
Thinking that if I can get a fast annealing - without risking the pieces - the kiln will cool faster and I can do my second firing in the afternoon.

Don't know why I keep coming back to this post, but here are some more thoughts:
Are you firing each object twice? If so, you may be able to use a faster schedule on the first firing including an aggressive anneal while using a more conservative schedule on the second firing since that firing will remove stress potentially induced in the initial firing. I'd especially look at heat up and cool down not just the annealing portion of the schedule. Can you remove plugs to speed up cooling? Do you fire over-night? - seems obvious, but thought I'd ask. Can you reduce the mass of shelves/posts?

The reference I always suggest, Firing Schedules for Glass, has time-based firing schedules which may be of use to you. Aslo, more conservative schedules are identified by moving from the indicated thickness of your subject project to thicker project schedules; I suppose you could reverse that process and move in the opposite direction to a schedule for a thinner project especially on initial firings. The schedules also have a time estimate which may help you select schedules as well.

[Stephen Richard]

Throughout this discussion on "how fast is safe" there has been no mention of stress testing at the end of the process. That will tell you if the annealing was sufficient. If there is significant stress, slow the annealing down.