IS GLASS HOT, WARM OR COLD?

Ask a silly question and you get a silly answer.
In the glass scene lots of terms are still used which formely -in order to be understood in the glass factories where they were originally used- had their own logical meaning. The Americans, with their craze for using snappy buzzwords, invented the term ‘hot glass’ and so -on the basis that, in the land of the blind, the one-eyed man is king- there presumably also had to exist something called ‘cold glass’! Nowadays, with the apparent need for the use of terminology in describing all forms of glass techniques, the situation is becoming something of a muddle. The time has now come -especially since the glass-working and glass-processing industry has already been using serviceable terms for many years- for us to learn to use them too!

Neues Glas recently published an article, entitled ‘Hot and Cold’, about the triennial exhibition Sculpture in Glass, organized in Luxembourg by the Generale Bank, Liège. The term ‘hot glass’ was used to cover blown glass, glass sculptures and studio glass, whilst ‘cold glass’ was applied to all other works made of glass. However, these are incorrect terms, which have no meaningful function outside glass factories and glass studios. The terms in question first originated from the categorization of techniques and the order applied in the production of works manufactured in the glass-blowing industry. After the glass-blowing itself -a process which naturally involves heat, since it entails the direct working of the hot molten mass from the glass melting furnace- there followed, logically enough, the techniques of warm and cold working. Examples of those techniques are to be found in annealing with enamels, which is a warm working technique, and cutting or polishing, which are cold workings. The old-fashioned terms likewise appear, for example, in the lexicon Moderne Nederlandse Glaskunst (Modern Dutch Glass Art), by T.M. Eliëns and M. Singeleberg-van der Meer, which contains a glossary of terms and concepts compiled by Sybren Valkema, a glass-blower whose descriptions of them derived from his knowledge at that time of his own specialist field.

Glas, by Thimo te Duits, published as part of the series Antiek Herkennen (to recognise antiques), also contains certain passages which, viewed from the standpoint of the disciplines from which glass originates, may be regarded as strange if those terms are also to be taken to indicate and describe other glass disciplines. The description of the process of adding luster, which forms part of the chapter entitled Hete Decoratie-technieken (Hot decoration techniques), only holds true if the luster salts are sprayed directly onto the object whilst it is still hot and freshly blown. For the sake of convenience, the book simply omits any reference to any of the other techniques involving the use of lustrous colours, in whatever form. Similarly, it is only in the glass-blowing industry that the word ‘decoration’ is used in that way to signify any technique which is subsequently applied. Artists and designers know better, however: that in art the decoration is not a ‘picture’ applied subsequently, by way of adornment, but emerges from the design process by which, moreover, the form is determined by the content of the decoration itself.

Hot, warm or cold glass?
There are only warm and cold working techniques!
If we would stop using those terms, we can still learn in the future to understand, by using them in the correct way, the context in which they properly belong. Now that the monopoly of studio glass has been broken, many things may be seen to have changed in the interim: flat glass has appeared on the menu of glass materials and techniques available, together with accompanying kiln-forming techniques such as slumping, fusing and sagging. Stained glass has been resurrected from the disrepute in which it was previously held and included amongst the flat glass-disciplines. Glass design has become more or less acceptable once again; glass is at last being taken seriously as an architectural material. It is readily apparent from this that today's glass world is clearly in need of better summaries and better ways of defining those concepts, in order to allow all the other disciplines -and not just studio glass- a place in the sun. Thus a new system of classification has developed, in which all the main groups are represented along with their respective techniques:

GLASS ORIGINATING TECHNIQUES comprise those which, in the manufacturing or fabrication process, involve the use of the hot mass taken from the glass-melting furnace. They include: injection moulding, casting, spinning, drawing, blowing, extruding, rolling and pressing, and salvaging or recycling. The form which the glass then takes covers flat glass, flashed glass, hollow glass (containers), and solid glass objects, as well as all the different variants, such as tiles, stones, tubes, rods, filaments, grains, pellets, nuggets, frits, cullets and granules which arise directly from the hot glass mass of the glass melting furnace.

GLASS WORKING TECHNIQUES comprise the working of glass in all its manifestations, with a distinction being drawn, where necessary, between cold or mechanical working techniques and/or warm or thermal ones. These concepts have been used for many years in all industries, but always in relation to working techniques. The concepts of ‘warm’ and ‘cold’ should not be used, therefore, in contradistinction to originating techniques (formerly known as ‘hot’ techniques), they serve to classify all forms of working techniques applied to articles which have previously been manufactured. Thus woven cotton can be printed (cold) or dyed (warm); similarly, a drinking glass which has previously been blown can be worked by applying a sandblast motif (cold) or a burned on transfer (warm). By the same token, even food can be worked to good effect in its cold or warm state.
Drilling, grinding, polishing, carving, cutting, breaking, engraving, etching, sandblasting, water-jet cutting, milling and sawing, cold enamelling and the application of 2-component colours constitute the cold working techniques. The warm working techniques comprise -in addition to hardening- gilding, silvering, staining, the application of glazing enamels, grisaille and contour, metallics, interference and other special paints, powders and pigments, together with the creation of mirror effects, abrading, matting and frosting, refining and finishing, depositing by vaporization or coating by all sorts of techniques such as painting, stippling, stenciling and rubbing by using transfers, embossing, spraying and air-brushing, splashing, printing and silk-screening and the like.

GLASS PROCESSING TECHNIQUES are techniques for transforming glass, in whatever form the glass may previously have been produced or worked and/or assembling it for the purposes of final construction. Here too, the techniques could fall into categories, according to whether they are mechanical and/or thermal in nature, and comprise leading, casting glass in concrete or epoxy resin, glass appliqué, bonding, gluing and cementing, making glass mosaic or mosaic glass, setting in copper foil; all kiln-forming techniques such as making pâte-de-verre or pâte-de-cristal, melting, enclosing, fusing, slumping, sagging and kiln-casting; all flame working techniques; bending and transforming. Also included are the techniques applied by the glass-processing industry such as the manufacture of insulation glass and safety glass, laminating, plating and sandwiching glass. Thus all assembly techniques that process the glass in flat or three-dimensional form belong to this group.

Now that the first patents are in force in Germany in relation to the invention of glass having a very low melting temperature, it is clear that everyone should henceforth apply the new system of classification. We should only continue to use the terms ‘warm’ and ‘cold’ in relation to specific warm or cold working techniques. In future we need to decide if the terms additive (adding paint) and subtractive (remove flashed glass layer by etching) are more useful terms within the working techniques.
I for one no longer wish to hear anyone say to a glass fuser: "Oh, so you work with warm glass?", or to a stained-glass artist: "You must be a cold artist, then!"

The terms ‘warm’ and ‘cold’ are clear now. There still remains the term ‘hot glass’.
This term can of course continue to stand for the purposes of indicating the superior skills of glassblowers; but have you ever heard anyone use the tautological expression ‘cold ice’?
Come off it!

Angela van der Burght
Translation James Benn

This side Up! March 4, 1998