Float Glass Experiments

It is well-known in kiln forming circles that float glass is inclined to devitrify with long, slow or repeated firings.  I decided to try to take advantage of this for a panel.

I shingled the strips of float and fired them at 835C for 10 minutes.  I expected a striped result with devitrified surfaces alternating with clear cut edges.

I didn’t get it, though.  Instead there were areas of mild devitrification, but no strong bands.

top, general view

View of the top ends of the strips

General view of the bottom

Detail view of the bottom ends of the strips

There was some evidence of devitrification at the ends of the strips where points were formed. 

Some pointed ends showing devitrification

Even when viewed in detail, there is little evidence of devitrification.  I continued, to do a slump, but even then, the tin bloom and devitrification did not show strongly.  Sometimes when you want an effect, you are unable to provoke it.

Float Glass Experiments

I have been conducting some recent experiments with float glass strips.  The intention was to play with devitrification.  

I placed the strips randomly tin or air side down.  In the first they were shingled, and then fused. In the second, they were shaped first then fused.  The first went into a self-made ceramic mould.  

Assembled strips fused and formed

Strips bent and assembled before fusing and forming

The second I decided to make into a large tray.  The mould for this, as I had no suitable mould of the correct size, became cut kiln shelves arranged in a parallogram and covered with thinfire.  

"Free form" mould assembled on sand bed

I fired at 100C per hour and watched periodically from 600C top 720C.  I decided to stop the firing after 10 minutes at 720C.  This was not an entirely successful experiment, as only a little devitrification shows on the first and none on the second tray.  Still, I obtained two interesting vessels, which encourages me to continue the experimentation.

A Powder and Frit Fused Panel

An example of how the studio and equipment hire works in the studio occurred yesterday. A few weeks ago an artist from South West Scotland rang up and booked the kiln and a studio bench for a day. Thursday was agreed upon after discussion of her requirements. I essentially provided the space for her to realise her work in glass.

She worked with a sheet of 10mm float glass and powders which she over layed onto the glass with a small canister with a fine screen as the top. Throughout the day the image began to appear. The real difficulty in doing this work is judging the depth of colour that the powders will produce. Obvious piles of powder and frit will produce more dense colour, but it is not always easy to tell where the powder is thin, even when done over a light box.

This is the panel prepared and sitting in the kiln ready to fire.

We discussed the differing firing characteristics of our two kilns. Where she would go to 795C for a full fuse of float glass in her 400mm square kiln, I go to 835C for 40 minutes in my 2 metre kiln to get an invisible seal of two or more sheets of float. Since this was already a single layer, that temperature and soak was not necessary. She wanted a bit of texture, but not a rough one, so we settled on 825C for 10 mins. She was also unsure the effect of size, ca. 650 by 750mm and thickness in relation to the smaller work she does in her kiln. So we settled on a modification of Stone's schedule for 10mm glass - a little slower heat up and a little longer annealing soak (a lot longer actually).

I'm happy to say that when she came in this afternoon, she was pleased with the result.

The finished piece still in the kiln.

The piece came out of the kiln with a profile so that the frit pieces were noticeable, but not sharp or lumpy. Everything was fire polished and shiny. Notice how much brighter and more intense the colours are after firing. The variations in density of colour is related both to the thickness of the powder application and to the amount of frit applied. Some is more obvious than in other areas. Where she applied frit over the powder, small clear halos appeared. She had planned for this and compensated by applying more powder over the fritted areas.

This is one example of how I work with an experienced glass artist. Artists and enthusiasts who are not so experienced get a bit more involvement from me.