how to alter firing to avoid devit

[seachange]

Hi,

I am fusing 2 layers of 1/8" float, with paint and inclusions in-between the layers. After months and months of endless tests and frustrations, have finally worked out a firing schedule where the inclusions don't cause any mayor bubbles, and the edges of the plates are acceptably rounded.

This is one big hurdle out of the way. But, I still get devit when I slump, sometimes in up to about 30 to 40% of the pieces in any firing.

Evidently there is something I don't have quite right yet, but have reached the point where I don't know what to improve, without risking the gains made regarding the avoidance of bubbles and rounding of edges.

I am wondering if someone could please help me to make some changes to the firing schedule. If it looks strange, it is possibly because of the adjustments I have need to make to eliminate bubbles around the inclusions.

Some info about the process:

I buy the float glass from an Australian manufacturer, to hopefully get even quality and characteristics from plate to plate.
Grind all sides and corners of each piece with a fine grinding bit (600) Found 400 to be too coarse.
Wash and dry everything really well.

From this point I handle the tops only with clean cotton gloves, and hold them only on the edges.

The top of the top layer is cleaned extra, with alcohol.
I apply the homemade borax mix (borax, water and a tiny bit of soap). This has helped somewhat, but hasn't solved the problem.

Set the top on to the bases (these are already in the kiln) and fire (I don't let the borax dry overnight, though not sure if letting it dry would be better or worse).

Schedule to fuse the blank (numbers are odd because they are converted from degrees C to F)
482 - 1100 - 30'
131 - 1202 - 0
752 - 1472 - 0

I crash cool to 1000 to get quickly out of the devit zone

Somewhere in that schedule the conditions for the devit must be created. However, the blanks come out totally shiny.

I often lift the cold blanks (with clean cotton gloves) out of the kiln, place the molds straight away on the shelf, blanks on the molds and slump. Thinking that this avoids unnecessary handling and the risk of any dust in my studio contaminating the blanks.

It is during the slump that the devit shows up. I find this strange, because I slump at 536 - 1182 - 4', which I understand is well below the devit range.

The kiln is an Evenheat coffin type, with elements on the lid and side walls. I always leave the peephole open for venting through the whole firing and the slumping, don't know if this is sufficient.

Have lots of orders for this project, but unless there is a way to avoid the devit problems, I feel like I'll have to give up on it.

Very much hoping for your help

Many thanks, seachange

[Bert Weiss]

It is not devit, but tin bloom. When you compress the tin side, it fogs up only where it is compressed. So, the solutions are either to layer up so there is a tin side down and air side up, or try using borax or spray A, and fire at least to 1400ºF for your slump. Float can handle that.

[Kevin Midgley]

ditch the alcohol.
It often contains an oil.
Clean with calcium carbonate, whiting.
Ditch the borax.
I never had any luck with that.
If and it is a big IF the glass is good you don't need it and it will otherwise just cause problems.

As for the glass, it is float. Float is notorious for misbehaving.
You are having bad luck with the glass you are getting from your supplier.
Change your supplier.
Over the years I've fired literally many tons of the stuff and I am giving up on it.
When the float glass I've got is gone, that will be it.
I am not going to buy more.
I can have test sheets sent to me before purchasing a 'load' only to find
the glass I received behaved differently even though the glass came from the same crate.
You have to arris the edges in order to get the glass to go round. Bullseye (you probably can't get) or Baoli (you probably can get) would not need that.
What you save on the price of float you spend on grinding and frustration. I even built a machine to manually feed/arris a 30cm square piece of glass in 12 seconds.
I can't be bothered any more.
If you insist on firing float may I recommend Japanese glass which has a slight blue tint to it rather than greenish and fires wonderfully. However they do not export it any more as their domestic market uses it all. I have not seen any for almost 35 years.
My recommendation would be to switch to the Baoli if located in Australia.
Saves the grinding and the grief.

[Bert Weiss]

ditch the alcohol.
It often contains an oil.
Clean with calcium carbonate, whiting.
Ditch the borax.
I never had any luck with that.
If and it is a big IF the glass is good you don't need it and it will otherwise just cause problems.

As for the glass, it is float. Float is notorious for misbehaving.
You are having bad luck with the glass you are getting from your supplier.
Change your supplier.
Over the years I've fired literally many tons of the stuff and I am giving up on it.
When the float glass I've got is gone, that will be it.
I am not going to buy more.
I can have test sheets sent to me before purchasing a 'load' only to find
the glass I received behaved differently even though the glass came from the same crate.
You have to arris the edges in order to get the glass to go round. Bullseye (you probably can't get) or Baoli (you probably can get) would not need that.
What you save on the price of float you spend on grinding and frustration. I even built a machine to manually feed/arris a 30cm square piece of glass in 12 seconds.
I can't be bothered any more.
If you insist on firing float may I recommend Japanese glass which has a slight blue tint to it rather than greenish and fires wonderfully. However they do not export it any more as their domestic market uses it all. I have not seen any for almost 35 years.
My recommendation would be to switch to the Baoli if located in Australia.
Saves the grinding and the grief.

Kevin

Most all my work is done with float glass. I don't work with anything thinner than 6mm and my glass of choice is 10mm. For arrissing the edges, I use either a 1.125" wide belt sander or a diamond hand pad. The hand pad is sufficient to save my fingers from cuts when cleaning and stopping breakage on heatup from microstarts. The very best glass cleaner is ethanol (vodka). I use a commercial glass cleaner called Glass Plus, based on this solvent. They don't have to pay the taxes on their ethanol. Isopropyl, as Kevin says is not so good. It is true that float glasses vary according to manufacturer. Some are more cooperative than others. I find it essential to know where the tin side is. All of the lessons of how to work with float took me way longer to figure out than I might have guessed it would take. I tend to avoid the borax thing, but sometimes it can do the trick. Other times, it can cause more problems than it solves.

The most important float rules are: Always use kerosene or comparable cutting oil. I paint it on my glass before cutting. Always fire tin side down. If you don't the surface will be rough. If you are slumping, always fire air side up. Learn to really clean the glass and to "see" the dirty spots. When using colors, you have to test for tin side contact. Some show no changes, others slight changes, and others horrible changes.

Float glass is a commodity, so what you buy today may be different from what you buy tomorrow. I am fortunate that I can find out from my supplier what manufacturer they are working with. They have a primary supplier, and several backups. But they do know what is what.

[Bert Weiss]

ditch the alcohol.
It often contains an oil.
Clean with calcium carbonate, whiting.
Ditch the borax.
I never had any luck with that.
If and it is a big IF the glass is good you don't need it and it will otherwise just cause problems.

As for the glass, it is float. Float is notorious for misbehaving.
You are having bad luck with the glass you are getting from your supplier.
Change your supplier.
Over the years I've fired literally many tons of the stuff and I am giving up on it.
When the float glass I've got is gone, that will be it.
I am not going to buy more.
I can have test sheets sent to me before purchasing a 'load' only to find
the glass I received behaved differently even though the glass came from the same crate.
You have to arris the edges in order to get the glass to go round. Bullseye (you probably can't get) or Baoli (you probably can get) would not need that.
What you save on the price of float you spend on grinding and frustration. I even built a machine to manually feed/arris a 30cm square piece of glass in 12 seconds.
I can't be bothered any more.
If you insist on firing float may I recommend Japanese glass which has a slight blue tint to it rather than greenish and fires wonderfully. However they do not export it any more as their domestic market uses it all. I have not seen any for almost 35 years.
My recommendation would be to switch to the Baoli if located in Australia.
Saves the grinding and the grief.

Kevin

Most all my work is done with float glass. I don't work with anything thinner than 6mm and my glass of choice is 10mm. For arrissing the edges, I use either a 1.125" wide belt sander or a diamond hand pad. The hand pad is sufficient to save my fingers from cuts when cleaning and stopping breakage on heatup from microstarts. The very best glass cleaner is ethanol (vodka). I use a commercial glass cleaner called Glass Plus, based on this solvent. They don't have to pay the taxes on their ethanol. Isopropyl, as Kevin says is not so good. It is true that float glasses vary according to manufacturer. Some are more cooperative than others. I find it essential to know where the tin side is. All of the lessons of how to work with float took me way longer to figure out than I might have guessed it would take. I tend to avoid the borax thing, but sometimes it can do the trick. Other times, it can cause more problems than it solves.

The most important float rules are: Always use kerosene or comparable cutting oil. I paint it on my glass before cutting. Always fire tin side down. If you don't the surface will be rough. If you are slumping, always fire air side up. Learn to really clean the glass and to "see" the dirty spots. When using colors, you have to test for tin side contact. Some show no changes, others slight changes, and others horrible changes.

Float glass is a commodity, so what you buy today may be different from what you buy tomorrow. I am fortunate that I can find out from my supplier what manufacturer they are working with. They have a primary supplier, and several backups. But they do know what is what.

[seachange]

Dear Bert and Kevin

Thank you for your replies, and sorry for the long delay to post, the work load at this time of the year has been a bit overwhelming.

The devit is truly devit, in this case it is not compression. The molds are really shallow, BE 8997 in 3 sizes. Also the appearance is of devit, tin bloom looks different

Have checked my alcohol, and found that I have two different purities, 99.5% and 70%. Have found local source for 100%, so I'll be trying it next ( prefer this to the whiting, but of course only if it works).

Unfortunately can't use 10mm glass for my work, it would be nice though.

The borax does help, and sometimes I can rescue some of the plates with the devit by flattening (with borax) then re-slumping.

After much reading all over the internet, have also improved the ventilation following Steve Immerman's suggestions from his website. This is certainly increasing my success rate.

Did remember that Rosanna has often mentioned here the importance of venting to 1000F.

Will do a few more with the venting. If I don't get 100% success I'll try borax and slumping at 1400F like Bert suggests. I usually slump at 1182F, this way I get the shallow shape without any pulling in at the edges...will have to test.

Many thanks to you both for all your help, seachange