Clay Arts Utah dedicated to education and advancement of the clay arts
Register  |   |   |  Latest Topics
 
 
 


Reply
  Author   Comment  
ClayArtsUtah

Avatar / Picture

Moderator
Registered:
Posts: 204
Reply with quote  #1 
Originally Posted on: Jul/31/2005 9:40
 
Glass Fired with Pottery
 
Okay, contuning my questions on multi media, has anyone played with glass in the kiln?

In glass work, when fusing two pieces of glass they must "match." This is what potters call fit. We all know that a improper glaze recipe will not fit with the clay and will craze or worse. People working in glass use specially formulated glass so that the fit matches when they fuse two pieces together. Unfortunately, those glass makers that have perfeted the fit between sheets of glass, do not make glaze. So potters are left with a problem of matching the glass to the glaze (which is, after all, just glass).

In glass work, glass is fused at about 1480 degrees. This does not melt it into a liquid pool, it just seals two pieces together and softens the edges. However, in glass fusion the kiln is different from a pottery kiln. Their kilns have elements in the lid so that the heat in directed down from the top.

I want to know what a pottery kiln (gas or electric) does to glass.

I have seen glass marbles in the bottom of a glazed bowl fired in cone 10 redux by Hiro Iwasaki. The marble melts to a pool of clear glass. The pool of glass crazes since it does not actually fit with the glass of the glaze. I wouldn't use it for soup, but it looks cool.

I would love to hear other experiences.

- Dawn
 
--------------
 
Dawn,

Glass in th kiln makes just what you said. a pool of crazed glass. Too much and you end up with a lovely colored shelf. AIf your piece happens to crack, you have just added glass to your shelf, as ifa student overglazed a pot. Due to the crazing, I have never used this other than tests to show students what happens. It make all work non-food safe, due to th potential for chipping.

John Shaw told me that they used to hang Coke bottles up in the kiln and let thm melt until they touched the shelf...creating a 30 inch very thin coke bottle. I don't think th new ones would work, too thin. (not clay related, but pretty cool.)

ken
-----------
 
dawn
you can apply the glass after you have fired to glaze temps. a glass kiln is not nessary. take the temp up very slowly. watch it melt. electric is best. i have used enameling glass and powder on lots of stuff. very cool shapes (thin strings) and great colors. window glass cut too shapes will work. temp is vary important!! watch it melt. cool slowly. the glass will craze if it sticks to the clay. sometimes i would use a resist (powered alumina or others) to keep the glaze from adhering to the form. it would take on the surface shape without cracks and i could glue it on later.
kevin

Dawn

Avatar / Picture

2006 Past President
Registered:
Posts: 225
Reply with quote  #2 

I have been doing a lot with clay and glass since my post last year.  It works amazingly well.  Two things are needed:  An electric kiln with a computer (not a cone kiln sitter) and true art glass (I use Bullseye Brand which is COE 90)

 

A computer controlled kiln is needed because glass must be annealed during the cooling process, or it will shatter.  With small pieces, a tightly closed kiln will probably work, but anything over 6 inches needs the temperature decrease to slow between 950 - 700 degrees.  Although you could watch a pyrometer and hand control a kiln, a computer is best.  For large pieces, a glass kiln is needed with elements in the lid, but for smaller pieces, a pottery kiln works.

 

Second, art glass gives you predictable temperature needs.  Bullseye glass slumps nicely at 1300 degrees, fully fuses at 1480 and needs annealing between 950 and 750 by slowing the cooling to no more than 150 degrees per hour.

 

Art glass uses a measurement of COE to determine compatability.  In pottery terms this is a measure of "fit."  In the same way that some glazes have a good fit with the pottery, other shiver or craze due to bad fit.  COE compatable glass will fit with other glass with the same COE without shivering or cracking due to incorrect fit.  The fit with the clay is not as important as with glaze because you would not completely coat the pottery with glass.  If you want to do that - use glaze.

 

I will post complete instructions for firing with glass next, but I thought some photos would be good here.

 

 

 

Attached Images
Name: glass1.jpg, Views: 3732, Size: 4.74 KB

Name: glass2.jpg, Views: 3713, Size: 12.07 KB



__________________
Dawn Atkin

Dawn

Avatar / Picture

2006 Past President
Registered:
Posts: 225
Reply with quote  #3 

Glass should be fired in two stages.  First a fuse fire to blend the colors together into a flat piece.  For a fuse fire (remember this works for Bullseye.  Other brands may be different.)  Adding clay means at least one more step to bisquefire the clay.

 

Fuse Fire the Glass

Room temp to 1100 at 400 degrees an hour

1100-1300 at 250 degrees an hour

1300-1480 as fast as possible then hold 10 minutes

1480 to 950 as fast as possible (Flash vent is best)

950 -750 at 150 degrees per hour.

Let kiln cool naturally to room temp before opening (Okay 200 degrees if you are impatient like me.)

 

Prepare the clay piece.  I have been doing a bisque fire to 06 then saggar fire to color the piece.  The saggar fire colors are not harmed by the slump fire for the glass.

 

Slump Fire the Glass

Place the fused glass on the pottery inside the kiln.  Use a release agent if you want to remove the glass after firing then attach with glue, or other methods.  However, it does not stick well even without any release agent.

 

Room temp to 1100 degrees at 400 degrees per hour

1100-1300 as fast as possible hold for 5-20 minutes until the glass slumps (keep an eye on it through the peep)

1300-950 flash vent to stop the slump

950-750 at 150 degrees per hour

750 down, allow kiln to cool naturally.

 

Give it a try.

 

-Dawn

 

 


__________________
Dawn Atkin
Dawn

Avatar / Picture

2006 Past President
Registered:
Posts: 225
Reply with quote  #4 

One more example...

Attached Images
Name: DawnAtkinGlass3.jpg, Views: 3729, Size: 7.17 KB



__________________
Dawn Atkin

GeckosNorwich

Registered:
Posts: 1
Reply with quote  #5 
IMG_1876 (761x800).jpg 

I have been using glass with my clay work for years, but as a self taught artist it's almost always hit or miss, but I must say I'm rarely disappointed - the piece above is a recent experiment fired from drying out and missing the biscuit firing to 1150c. The glass is from a stained glass shop in the scraps box and I smashed it in newspaper before sprinkling into the circles.


__________________
Self taught in hand built pottery and clay wall art since 1993.
Dawn

Avatar / Picture

2006 Past President
Registered:
Posts: 225
Reply with quote  #6 
Lovely piece.
__________________
Dawn Atkin
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.