Dedicated to glass and the ways it can be used to make beautiful works. The content of Cooking Glass spans basics such as cutting glass, through to the technical challenges of kilnforming and other Hot and Warm glass processes; and explains how to choose, maintain, repair, and build kilns and other equipment.

Overview

Glass was born of fire...

From the time our primitive ancestors first found some strange crystals in the remains of a cooking fire, heat has always been integral to the working of glass. Glass and pottery have close links. Like pottery, it is made by applying heat to the most common minerals making up our world. The glost on the surface of pottery is glass. The same mineral oxides used to paint pottery are also used to colour glass. Many glass artists start out as potters. Many glass artists use pottery kilns in which to fire their work and most kilns sold as glass kilns are modified versions of pottery kilns. There is much more on this in the technical sections of this site, but here we wish to outline in simple terms how and where glass impacts on us and our surrounding.

Glass was originally discovered by accident, modern science and ingenuity has provided an extensive range of formulations and processes to add special or unique capabilities. They include:

  • Self cleaning windows for the highest of tall buildings
  • Glass of a range of colour to rival that of the rainbow
  • Heat resistant cookware such as the inimitable ‘Pyrex'
  • Beautiful objects to adorn and to give joy to the eye and to the soul
  • Glass which can regulate heat or light to improve the comfort of the home
  • Laboratory glassware to facilitate the most complex scientific and medical research
  • Jam in a jar with a well sealing lid

Truly a mixture of the sublime and the mundane

The glass of art is the same as the glass of architecture and of bottles and jars. It can be cut and sawn, ground drilled and polished, painted or coloured, stretched or bent, made to take up intricate shape by melting casting blowing moulding or other techniques.It is available as sheet rod or tube, as powders or frits, or even as bags of blended mineral earths for melting in a furnace.

Glass and colour

Most glass is clear, or nearly so. Architectural or window glass has a touch of green due to iron in the sand. Add  some mineral ‘herbs and spices’ and it becomes clear as in jars and bottles; or more expensive window glass. Some colouration can be just a tint of green grey or blue and have architectural application. It is made by the float process and in very large sheet sizes. Add other blends of mineral oxides and the result can be coloured-right-through glass of most of the colours of the rainbow. When sold as ‘art’ glass, it is rolled out in thin sheets and may be clear, a single colour or a mix of several; often of very pleasing design.

Edge shot? 101-1

A bit of history

Archaeologists and historians tell of glass objects dating back thousands of years, and these have been chronicled in numerous books on glass art. In times more recent but to us still ancient were developed methods of colouring glass and of blowing glass bubbles, cutting and flattening them to make sheet glass.

The glass was then used to produce the remarkable stained glass windows which commenced to adorn Cathedrals and Palaces throughout Europe.

Thus were born the glass activities which are today labelled ‘Hot Glass’ and ‘Cold Glass’.

By the mid to late 1800s methods of making both clear and coloured rolled flat sheet had been developed as had the making of both ornamental and utility items by casting and pressing. Flat sheet was made first by ladling the molten glass from the furnace onto a flat surface and rolling it flat, still later by passing the molten material straight from the furnace to the rollers. Much rolled glass is still made this way.

The glass of commerce

Glass was very much the glass of commerce. In the period from the late 1800’s up to the first World war, giant strides continued to be made in the understanding of glass as a material and of mass production techniques in general.  Much of our standard literature and  insights into manufacturing processes and the colouration of glass date from that time. Even today, that any closure should fit on any glass jar, and be made at such low cost, is indeed noteworthy – if given little heed. Long established glass makers continued to expand and new operations blossomed in both Europe and elsewhere, notably in USA. In the forefront were Pilkington in England and Corning and Owens in America.

Objects which today are valued as collectables were made in factories by workers either blowing or casting mass produced glass pieces. They did this by drawing the glass from a central furnace, often as an adjunct to the principal operation of the business. It was in this period that processes such as pate-de-vere were developed and artists such as Tiffany flourished. European art glass makers such as Verrerie De St Just had long flourished and American operations such as Kokomo Blenko and Wissmach were established.

Glass has always needed tender care whilst cooling so that a kiln in which to cool it has ever been as essential as the furnace in which to make it. Developments in steel making and ceramics firing meant that industry was well supplied with kilns to accept the largest of objects so that in the time between the wars giant cast glass objects such as the 200 inch (5 metre) diameter Mt Palomar telescope mirror were able to be crafted. 

Post 1945

Wartime developments had seen remarkable advances in technology overall and in kilns and furnaces in particular, even though some were slow to catch on. Up to that time those wishing to shape or fuse ready made glass had to use giant kilns built to fire ceramics or heat steel.

Thinner and more corrosion resistant steel sheet and better high temperature insulation allowed for the making of smaller and more efficient kilns with more precise temperature control. Activities taking advantage of this became labelled as ‘Warm glass’ and the term ‘Kilnforming’ has latterly been coined to describe the numerous operations.

Studio Glass Movement

In the 1960’s there was a move toward artists working in small independent studios producing one-off items. This became known as the Studio Glass Movement. It gave rise not only to a demand for formal training for artists but also for glass with a wider colour range and greater depth and brilliance. For a concise outline of this movement see the Wikepedia entry on Studio Glass.

In Australia, formal training centred around Technical Colleges and ‘Colleges of the Arts’ which became absorbed into Universities. This gave rise to a method of training centred on the ‘Art’ at the expense of the ‘craft’ and much ‘reinvention of the wheel’. That training model has become too costly to maintain so the number of institutions offering training are reducing; most recently with the withdrawal of Monash Melbourne. It is likely that before long only two will survive. Even in the training of glaziers in the TAFE system, where the need is more immediate, the cost of keeping up with equipment improvements has become so high that students are being trained on the use of the latest equipment in private business premises where the cost can better be absorbed.

There is much pretension surrounding glass as an art medium. Whether it be Art, Craft or both is often a subject of debate; even though debate be futile as advocates of a view will rarely be converted. With the two being linked together in the most glossy of journals a speaker at a recent glass conference introduced another term ‘artisanship’, possibly to further elevate in the speakers opinion the pedestal on which ‘art’ glass should be placed. Not clear was the relative ranking of artisan and craftsperson. This will undoubtedly be made clear in the fullness of time. Of course, to those with pretensions, ART is what they do, whether it displays good or bad craftsmanship.

My view, for what it’s worth; Art creates the vision splendid, Craft turns it into what puts bread and potatoes on the table. In this website I have given a charitable interpretation to the term ‘glass artist’. Who can say what lies buried deep inside even the least of us.

Blown glass pieces coming out of factories in Eastern Europe are currently being offered in Australia at a fraction of the price of items from local studio artists, and it is interesting that recent visitors to the region tell of groups of people drawing glass from a single large furnace and working in shifts to make best use of the facilities. Sounds like a return to the early 1900’s.

Art glass makers

At the time of the commencement of the Studio glass movement there were numerous existing makers of coloured sheet glass in both Europe and USA aimed mainly at serving the leadlight and stained glass window market.   In the early 1970's glass artists set about developing glass with more intense colour and this led to the establishment of Uroboros, Bullseye and Youghigheney, all producing rolled glass in separate cast sheets.

There being a dearth of information on re-firing sheet glass, (this a use to which the traditional makers of sheet glass didn’t intend their glass to be put) the makers recommended extremely slow heating rates and long soak times; causing devit problems for which lead based sprays such as ‘Spray A’ were introduced. Later, enginers with some continuous rolled sheet production experience set up to make similar glass by a process based on methods long used by commercial glass makers. This became Spectrum, using continuous casting for the base colour and hand ladle application of any other colour.

Competition between Spectrum and Bullseye gave rise to some ridiculous claims such as in the pamphlets authored by Gil Reynolds for Spectrum implying a beautifully smooth temperature/viscosity curve of Spectrum glass compared to that of Bullseye which zigged and zagged all over the place. This was challenged of course, proved wrong in court and withdrawn with apologies. The literature is still around; just don’t believe it.

More recently Spectrum has entered into marketing arrangements with Uroboros and Skutt kilns to offer such an extensive and complex range, directed mainly at the domestic hobby market with pre-programmed kilns and recipes for making knicknacks and whatnots. Bullseye have stayed closer to their Studio Glass Movement roots by sponsoring training and other activities to expand glass art.

All this has come about at considerable increase in material costs both for the glass artist and for the leadlighter who often has little option but to use compatible glass in non compatible applications. With increased cost goes reduced consumption and the demise of many art glass outlets. In Australia the number has halved in recent times, although there has been a growth in 'online suppliers'.

The art glass scene

Artists craft and trades people work with and manipulate glass in a variety of ways through a range of processes; and through a wide range of temperatures. One way of classifying them is according to the main operations of 'cold glass' 'warm glass' or 'hot glass'. Even that can lead to confusion because, as will be seen, activities are rarely confined to just one area but overlap considerably.

Appreciation of the beauty of glass and of the skill of the artist can be enhanced by some understanding of the glass process. For a slightly technical introduction see About the glass.

Below is a brief outline of what the activities encompass today;

Cold glass

At the “Cold” end of the glass-and-heat spectrum is the taking of ready made glass and joining it by leadlighting or copper foiling: simple methods of joining pieces of glass into intricate designs from the small window hanging or mobile, to ‘Tiffany’ style lampshades, to domestic window and door panels and vast installations in churches and public buildings.

Fig.101-4

On a more massive scale it includes the taking of large slabs or chunks of clear or coloured glass, cutting to shape and joining together using steel concrete or chemical bonds to create structures such as the Leonard French  roof in the Great Hall at the National Gallery in Melbourne.

Fig: 101-5

Often the chunks are especially cast to achieve a desired colour or shape; an example of the cross discipline nature of much glass work.

Hot glass

At the “Hot” end is glassblowing: skilled artists manipulating molten glass into intricate delicate and beautiful shapes. The glass is melted in furnaces at over 1300°C, frequently re-heated during manipulation in a ‘glory hole’, and shaped using a wide range of tools: the origin of some being traceable back many centuries.

Fig.101-6

In earlier times large cylinders of clear glass were blown slit and flattened to make window glass. Called mouth blown glass, it was wavy, of uneven thickness, and was painted to create the stained glass windows of the period.Today a small number of specialists, mainly in Europe, still practice this ancient method of glass making to aid the restorer in matching the colour and texture of ancient glass; or to create unique glass for special projects.The molten glass can also be poured into moulds to create objects which may be sawn ground polished, whatever.

Warm glass

In between is the  “Warm” zone, involving the re-working of already made glass using heat. Most operations involve the use of a kiln. The term Kilnforming has been coined to describe all those warm glass operations involving a kiln in which the glass is heated and shaped in the same operation and includes slumping fusing and casting. The kilnformer may take pieces of clear or coloured glass, cut them to create a design and then fuse them together to make a piece of art or utility. They may take portions of finely crushed coloured glass of various shades, arrange them on a clear flat piece in intricate design and fuse them together.

Merinda, seahorse.   101-7

Or, they may take the same crushed coloured glass of various shades, grind them even finer and use as glass paint to create designs or to apply areas of colour on clear glass shapes.

Maus, platter with paint    101-8

Lampworking

Named from the practice of using lamps burning town gas made from coal, lampworking  involves the use of gas torches as a heat source in diverse processes such as manipulating glass rod or tube to make animals figures or jewellery

Image ant by Arthur Sale  101-9  or Denise Image from Lampworking

Or sculpting large blocks of glass or applying extra heat to a hot item in a kiln,

Image  Cobi; 101-10

Or applying localised heat to a blown piece.

Image Eileen G with torch 101-11

Widely practiced in USA between the wars as a carnival sideshow entertainment was the making of glass novelty items using a gas torch to melt glass rod which were sold to the spectators.  Of course, to ensure the item was properly annealed it was placed in an annealing kiln and similar items mass produced beforehand were sold on carnival day.The practice continued after WW2 but gradually died out and practitioners were absorbed into the wider art glass scene.In Australia it was less widely seen but I have recently seen one person practicing his art or craft in a suburban shopping centre in this manner.

The making and repairing of scientific glassware calls for a level of skill and understanding of glass far in excess of that of most lampworkers. It is outside the ambit of this website, as its practitioners are few and the skills exclusive. They use ready-made borosilicate glass tubes and shapes to produce laboratory and other scientific apparatus, often to extremely precise specification.So rare is the talent that our leading institutions find it necessary to import scientific glassblowers from overseas. More on scientific glassblowing can be seen at Scientific Glassblowing Learning Centre

The areas of Art glass above described are sometimes defined in those terms, so that a studio specializing in one area may be referred to as a Cold Glass, Warm Glass, or Hot Glass Studio. This doesn’t mean that the three are separate and distinct. More frequently activities will overlap so that a leadlight studio may have a kiln to fire painted pieces for inclusion in their work. This is often the case when restoring leadlight panels in old houses or public places.Patterned glass previously used is often not available so, for a leadlighter to repair some beloved panel, the pattern or texture must be reproduced by creating it on a kiln shelf and slumping clear glass to match the old. Replacing a damaged painted feature requires skill not only in leadlighting but in matching the colours and firing techniques of yesteryear.

Kiln or Furnace

It may be wondered, ‘why the two names’. The answer is ‘tradition’.Traditionally, a kiln produces solid objects such as bricks or pots whilst a furnace produced molten material such as molten iron or steel; or glass. What’s in a name? To the kiln builder they are all heat enclosures.However, tradition does figure largely in the thoughts and studies of many glass artists as they seek to learn from or reproduce work from previous times; but still blend seamlessly into contemporary living.

In earlier times the wealth of Church and Royalty financed and encouraged much of the  development  of stained glass and the massive windows to adorn European Cathedrals and Palaces. It was only in more recent times that private citizens were able to beautify their homes with constructions of lesser size but of comparable beauty. Even today, the windows adorning religious or commercial buildings figure largely in tracing the changes in techniques used in their creation; irrespective of whether the theme be traditional or contemporary.

In Australia it was well into the 20th century before changes from the traditional lead-came and glass construction of lights began to appear. First came a move away from religious motifs in churches to a more bold contemporary look. Pieces of coloured glass were still held in place using lead came. Donor wishes for pastoral themes became more widespread as in the window in the Anglican church in Hastings Victoria commemorating its early history as a fishing port.

Other methods of holding the glass pieces were introduced, such as in works of David Wright where small but often complex coloured or painted pieces are supported in cutouts in large wrought steel panels which are often suspended on the inside of large clear glass windows. The supporting metalwork may be stainless steel which has been heated to produce surface colourations of black blue or bronze.

David Wright     101-14

Still another approach was that exemplified by the church windows at St. Francis of Assisi Church Mill Park Victoria. Titled 'The Canticle of the sun', it traces the life of the Saint and is the work of Christopher John and Dylan Thornton.  The lights consist of very large kilnformed panels each 900mm wide and around 1800mm high, with each being made up of layers of various sized pieces of clear sheet, painted and then fused together with coloured glass inclusions to create varying thickness panels with a minimum of construction members.

Image Chris B 101-15  Maybe images of detail also

In Australia’s short history we have amassed a vast number of stained glass windows in churches public buildings and private homes, chronicled by Dr. Bronwyn Hughes in her monumental digital work Lights of our past; now sadly a collectors item, but hopefully to be reissued. Like so much of modern digital  production, editions can quickly become obsolete with rapid technology updates and it appears that Lights of our past cannot be viewed on some of the latest computer systems.

NOTE. A window has two parts, a frame and the ‘light’ through which light passes; hence the title of the CD.

In the hot glass studio may be created paperweights or vases, perfume bottles with close fitting stoppers, flowing wall hangings or pieces of jewellery. The artist may gather a blob of clear or translucent glass, add layers of contrasting colour one on top of another and create a bowl. On the inside it displays the base colour whilst on the outside the last colour to be added. Expert use of cold working techniques such as copper wheel engraving, and untold hours of effort, allow the artist to turn this plain coloured bowl into a thing of beauty; as shown in the following images of the artist Alasdair Gordon at work.

Images Alasdair Gordon clip from Eileen G. 101-16

In the kilnforming studio the artist may cut masses of small pieces of glass of various colours and fuse and shape them into an object of grace with flowing lines and a brilliance of surface rivalling that of glass fresh from the fire. As well as a kiln, the artist will be surrounded by saws grinders and other cold working paraphernalia. Such is the environment in which Anne Sorensen may spend copious hours creating items such as that shown below.

Image Ann S blue white tall from CG gallery. 101-17

Giant kilns, heavy lifting tackle, strong muscles and months of patient effort may go into the crafting of massive glass castings such as that created by Charles (Chick) Butcher and shown below. So massive is this piece that the anneal stage alone took over 90 days with an accurately controlled change in temperature of less than 1°C in each 24 hours. Less precision and the block could have split asunder.  

Chick image  101-18

Cost of operation

Glass making and manipulating can be among the most energy intensive of all processes. Many dishes can be cooked with one heating of the kitchen oven. The potter can stack numerous items one-on-another when bisque firing. However:

  • When kilnforming, each piece must be kept clear of every other piece, fired only one shelf high and stay in the kiln until cooled right down to room temperature.
  • The difference in rates of shrinkage of glass and crucible as they cool means that the crucible may crack when the furnace is turned off
  • As a consequence the furnace in the hot glass studio must be kept firing 168 hours every week; often for months at a time.
  • Consider the large cast block mentioned earlier. The kiln, costing tens of thousands of dollars was tied up for around six months just for this one firing.

It is interesting that, unlike most other forms of art, glass artists rarely sign their work. The painter adds his signature, the cartoonist has his signature symbol, the potter embeds crest or initials. The failure of glass artists to follow suit may be partly because of the difficulty of marking such a hard material, or a reluctance to permanently marr their creation, but there are methods available by which it can be done.

This overview has barely touched on the complexities of glass and the processes and equipment used to manipulate it, nor of the immense contributions made by European artists and commercial operators over the years. Those who wish to learn more of the technicalities are invited to explore further through this site. For those whose interest is more general, the links below may be of interest. Australia has two organisations representing the various practitioners; Ausglass, billed as the foremost body for the promotion of contemporary glass in Australia; and Architectural Glass Design Australia, AGDA, the representative Association for the leadlight, stained glass, architectural and decorative glass sectors.

The work of many of Australia’s leading glass artists are housed in the National Glass Collection in Wagga Wagga Art Gallery in NSW.

Other sites worth visiting include:

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