Firing with glass

[nancylee]

Hi all, 

I had a brief foray into glass arts and have quite a bit of small pieces of glass and grit left. I want to fire with glass but no idea how to do it. Usually I bisque to cone 05 and fire to Cone 5, no hold with Laguna clays. 

Do you bisque first and then place the glass? Doesn’t make sense cause if a bowl, how would you get the glass to stick? Obviously, I’m clueless and any assistance would be very appreciated!!! 

Nancy

[Roberta12]

Nancylee, you can put the glass inside a bowl or even a shallow piece, and it will melt.  Yes, you can do it during the glaze firing.  I would glaze the bowl, and then put the frit or pieces of glass inside the bowl. Then fire to cone 5.   These bowls will not be food safe because of the cracks in the glass, but they are lovely trinket dishes.  Does that help?

Roberta

[LeeU]

You could also skip the bisque and insert the glass wherever, and single fire to ^5.

[LinR]

I have fired chips of glass stuck into the raw clay near the outside top of  a mug and then bisqued it.  I expected the glass to pop out but it melted and then when glazed gave a nice run of glass through the glaze. I have also used it in flatish wall pieces fired flat in the glaze fire to give an interesting highlight to an area.  If the glass is too thick it can cause the clay to crack either in the firing or much later on.  Tension problems I would guess.  Lin

[nancylee]

5 hours ago, Roberta12 said:

Nancylee, you can put the glass inside a bowl or even a shallow piece, and it will melt.  Yes, you can do it during the glaze firing.  I would glaze the bowl, and then put the frit or pieces of glass inside the bowl. Then fire to cone 5.   These bowls will not be food safe because of the cracks in the glass, but they are lovely trinket dishes.  Does that help?

Roberta

Yes, thank you very much!

Nancy

[nancylee]

4 hours ago, LinR said:

I have fired chips of glass stuck into the raw clay near the outside top of  a mug and then bisqued it.  I expected the glass to pop out but it melted and then when glazed gave a nice run of glass through the glaze. I have also used it in flatish wall pieces fired flat in the glaze fire to give an interesting highlight to an area.  If the glass is too thick it can cause the clay to crack either in the firing or much later on.  Tension problems I would guess.  Lin

Thank you, Lin, much appreciated!

Nancy

[nancylee]

4 hours ago, LeeU said:

You could also skip the bisque and insert the glass wherever, and single fire to ^5.

Thank you, Lee!

Nancy

[Stephen]

Ya know I've posted this before. I really don't mean to be lecturing but this really is the truth.

One of my relatives worked at the largest art glass manufacturer and she told me it was so hard for them to convince people not to fire glass and pottery together. It's not a matter of if it will eventually separate and fail it is just a question of when. That means at some point whatever you put together will fail and if it does so in a dangerous way someone will get hurt. Nothing will change that, glass and pottery are not compatible long term.

[Roberta12]

8 hours ago, Stephen said:

Ya know I've posted this before. I really don't mean to be lecturing but this really is the truth.

One of my relatives worked at the largest art glass manufacturer and she told me it was so hard for them to convince people not to fire glass and pottery together. It's not a matter of if it will eventually separate and fail it is just a question of when. That means at some point whatever you put together will fail and if it does so in a dangerous way someone will get hurt. Nothing will change that, glass and pottery are not compatible long term.

It's a lovely effect, but I stopped doing it because I would occasionally get a shard of glass that would pop loose.  I just didn't want to risk harm to a customer.  And no matter how many times we give the warning about not being food safe, a pot could always be used for just that purpose.  

[nancylee]

9 hours ago, Stephen said:

Ya know I've posted this before. I really don't mean to be lecturing but this really is the truth.

One of my relatives worked at the largest art glass manufacturer and she told me it was so hard for them to convince people not to fire glass and pottery together. It's not a matter of if it will eventually separate and fail it is just a question of when. That means at some point whatever you put together will fail and if it does so in a dangerous way someone will get hurt. Nothing will change that, glass and pottery are not compatible long term.

Oh, I hadn't seen your post before. Interesting. I was thinking of using glass in a little ring dish, nothing usable for food, but I guess the glass could still pop out and cut someone. Thanks.

[Rae Reich]

I visited a glass blowers' shop and picked up some pretty fallen blobs. I was warned that they would very likely shatter at some future time because they had not been put through the final long soaking heat (don't remember the term) that all manipulated glass needs to maintain integrity. Perhaps pots fired with glass inclusions would also need a final "cure"? Don't know what effect that might have on the glazes. 

[Roberta12]

12 minutes ago, Rae Reich said:

I visited a glass blowers' shop and picked up some pretty fallen blobs. I was warned that they would very likely shatter at some future time because they had not been put through the final long soaking heat (don't remember the term) that all manipulated glass needs to maintain integrity. Perhaps pots fired with glass inclusions would also need a final "cure"? Don't know what effect that might have on the glazes. 

I think that is called annealing?  a long slow cool  to strengthen the glass.  I hadn't really thought about that, but when you glaze fire with the glass in the pot, the temp is much higher than what you would use for glass work.  But what if you put the glass pieces in an already glazed piece and just took it up to glass temps and did a slow cool?  Glass temp would be around 1400 or so.  Hmmm  food for thought!  And Nancy Lee, I think all potters LOVE a good experiment.  Maybe this could be yours, even if you didn't sell them, you could just do it to scratch that curiosity itch! 

[Stephen]

26 minutes ago, Rae Reich said:

I visited a glass blowers' shop and picked up some pretty fallen blobs. I was warned that they would very likely shatter at some future time because they had not been put through the final long soaking heat (don't remember the term) that all manipulated glass needs to maintain integrity. Perhaps pots fired with glass inclusions would also need a final "cure"? Don't know what effect that might have on the glazes. 

As it was explained to me glass and clay just do not form a forever bond and can't be made to do so because of the underlying physics of the two. I don't want to name names in a public thread but they are a huge company with customers worldwide and they sell art glass and had every incentive to open that market. It is a beautiful effect but It just won't work with the only consistency being eventual failure perhaps years later..

The worst part of it is that is appears to work and may last some time. Even a non food surface will not protect anyone because art objects get picked up and moved around and who knows how it's going to separate. It could be one blob falling out of a ring dish or just tiny shards dropping around. It worried them enough to go around to places that posted instructions and try to explain to them the dangers and get them to pull the instructions. 

[Callie Beller Diesel]

I did just enough glass blowing and slumping to make me read up on the chemistry differences of both. Basically glass, unless *very* specifically formulated to be compatible with a specific clay body, have different (and mismatched) rates of expansion at all points of the heating and cooling cycle. I found one guy who managed to get the formulation right as part of his master's degree thesis, but both clay and glass were his own formulations, and neither is commercially available. And last check he wasn't working with the process anymore because it was too much of a pain. I will also repeat what Stephen said: it's not a matter of if it will fail, but when.

Annealing glass doesn't change the coefficient of expansion of either glass or ceramics, or the points at which the two substances expand and contract with heating or cooling.  In ceramics we really only concern ourselves  with one phase change at quartz inversion. Glass cooling cycles deal with about 5 if I remember correctly. All of them are at much lower temperatures than clay workers even look at.  

The firing cycles that you have to do to get glass to be glass and ceramic to be ceramic are also mutually exclusive. Glaze is a solid with some crystalline matrix to it: we all go on about how to slow our firings down at certain points to alow the materials to homogenize and have a chance to grow crystals for pretty effects. The opposite is true of glass: it's a supercooled liquid, and not actually solid at all.  That's why antique windows are thicker at the bottom than at the top: the glass is still flowing, it's just doing it really, really slowly.  

Glass artists will crash cool their kilns through the places where crystals develop to prevent devitrification (homogenization and crystal formation). Crash cooling a kiln at those places will cause dunting in clay.

If you're trying to incorporate stained glass into ceramics, you should also be aware that most of the colours in the glass are created with all kinds of things that burn out well before bisque temperatures. The toxicity level of these compounds is also pretty high (think arsenic). The colours will burn out, and also create all kinds of mystery fumes as the glass boils.

 

All that said, if you want to play around and have some fun with process, I do say go ahead and enjoy the experience of making. I think that's important. You will learn things. Just go about making them knowing that they are temporary creatures and won't last.  For liability's sake, don't sell these pieces or turn them out into the world. 

If you wish to incorporate glass and ceramic, I'd go cold process, and make friends with things like uv glue or epoxies.

[Rae Reich]

Great explanations, Callie and Stephen, thanks. 

I worked with a glass artist once making slab-sided candle holders carved with windows into which she used UV glue to attach her glass. I kept one for years outside (in SoCal) and have to report that the glue failed after a few years. Perhaps it was because of my choice of glaze or firing (^06), an unevenness of surface, or the mild fluctuations in temps. 

I would go with 2part epoxy. 

[fergusonjeff]

On ‎7‎/‎7‎/‎2018 at 3:59 PM, Callie Beller Diesel said:

That's why antique windows are thicker at the bottom than at the top: the glass is still flowing, it's just doing it really, really slowly.  

Just a quick side note.  Glass does not still move at normal temperatures.  This myth relates to old windows.  Many really old windows were made from blown glass that was flattened while hot and then cut to shape.  This often resulted in uneven thickness.  The glass was usually installed with the thicker sides on the bottom.  More recent (but still old) glass has a very "wavy" look and this was also from the initial manufacture, not continued movement after installation.  If glass was still moving, we would see some slumping in glass forms thousands of years old from many places in the old world.  Unless they are exposed to enough heat to start melting they do not move.  As an archaeologist I work with lots of volcanic glass (obsidian) artifacts.  There are many artifacts millions of years old, and aside from some surface weathering (usually a function of a slow hydration process) there is never any change to the overall shape even after hundreds of times more time than the old blown glass windows. 

The incompatibilities between glass and clay are a function of slight differences in expansion related to temperature change, not continued flow in the glass.   

[preeta]

Wow this is such a fascinating read.  I learnt so much.  

First I always look at traditional ware.  Clay lived right next to the origins of glass but the people never put them together.  Neither did any other culture in a big way to my knowledge.  

However, here in the US I have read the traditional potters in the Carolinas used glass to fix/fill in the cracks of their handles. I have no idea what glass they used and how it held up.  But I admire their ingenuity to fix problems.  

Carrying on in the glass tradition Mark Hewitt uses glass (wood fire) so ^12+  as decoration on the outside on functional ware.  Again I have no clue what glass he uses (away from the lips/rim) but he does use very tiny amounts. I don’t know his process.  

I feel there is so much, so many areas to experiment in ceramics that while I was interested in glass - after my research decided to stay away.  

Also the Persians used fritware. That was powdered glass mixed in with clay I believe. Don’t quite know the details. Or let’s put it this way, I no longer recall.  Or maybe they used glass mixed with clay on the surface to mimic porcelain?

If anything Nancy, if I had access to real coloured glass I’d make  murals out of them. In fact I actually have made murals out of my broken pottery shards and some tiles I made and presented them to friends with yards. Small ones. 18x24. 24x 36.  Unfortunately I used those coloured pebbles from Michaels and that’s how I realized what glass was.  Home Depot was my friend.