The making of fibreglass threads is mentioned analogue to textile techniques like spinning, weaving, twisting, crochet, making bobbin lace…. The substances from which end­less threads can be made are called filaments or elementary threads. Those with a certain length are called fibres. NB: Glass spinning is also considered a technical principle where a glass thread has been trailed or threaded and twisted from a hot mass onto glass container forms or into open basket-shapes. Filament threads consisting of one (mono) or more (multi) filaments, where the continuous length is extruded by a spinning nozzle with one or more holes is called chemical spin­ning. Fibre threads are made of fibres of a certain length that are equally divided and laid parallel, called fuse thread or pre-threads, then twisted together by a mechanical spinning. Twisting is simply, turning the fibres into one single thread and to twine is twisting two or more threads into a thicker, stronger or multi coloured threads. By plaiting and weaving threads we form tissues. Felts or membranes arise from loose fibres, called dry wadding or wet (glued) felt. After stitching, these type of glass fibres are called needle mat or felt.

The technique of glass fibres arose in the 1930’s through experiments with pulling glass threads horizontally and vertically out of glass bars. A lot of glass factories in the Thüringerwald, Germany, already made hand-drawn tubes, bars, and rolled glass marbles as semi-finished products. 'Angel-hair' are bundles of very tiny, blank glass threads drawn from bars that became an attribute of traditional Christmas decoration.

Joseph Schuller of the Wernhütte at Haselbach, Germany, was the owner of such a factory who invented the bar-barrel-procedure in 1931, in which bars were heated by a gas flame until liquid drops appeared that could then be drawn or pulled out into finer threads. These threads were immediately wound onto a barrel, now and then cut. The velocity used for drawing it out determined how thin the thread would become. In 1936, Schuller succeeded in obtaining the twistable quality from the hot glass mass, which was the cradle of textile glass fibres. These first attempts at making glass fibres membranes for insulation used in post-war houses, began in 1948. Schul­ler's son Wolfgang improved this technique. Soon after, a single machine could produce 30 square metres per hour. In 1952, glass fibres membrane had developed as bitumen used on roofs and for making of tube bandages for large synthetic tubes. When the factory moved to Wertheim, where the new machines were constructed, this produced 1.8 million square metres of glass wool in 1953. Today, this production has increased to include the same quantity, but, in only half an hour!

Weaving mills made insulating and technical tissues out of glass fibre threads. In 1960, Schuller also opened the doors of a factory for producing fibreglass wall paper-repla­cing the jute tissues of wall covering and filters. In 1954, Schuller built factories in Canada and sold the licenses and machines to the rest of the world. In 1971, the family sold the company to the Johns-Manville Corporation, in Denver, USA. In 1972, a new factory was built to produce pallets as basic material for the fibreglass industry. In 1973, this factory established a twiner in Wertheim where glass fibres could be manu­factured into threads. By the time the health dangers of asbestos proximity and inhalation were understood, all its fibres could be replaced by glass threads and industrial glass insulation tissues including blankets for covering kilns and the tunnel belts for coolers. NB: Asbestos and Chrysotile is a natural material of tiny microscopic and needle-like fibres, mainly consisting of silica or mineral fibres. The Romans used it for lamp wicks and cremation cloths. Forgotten in the Middle Ages, Marco Polo brought the knowledge back from China where he had seen “fabrics not burning in fire.” The material’s inexpensive, excellent insulating properties were lost forever when its use was prohibited in favour of people’s health.

Wet fibre machines produce broad glass membranes for an underlay for PVC floor coverings or raw glass membranes used layered with other materials, where several properties can be improved by adding synthetic materials. In 1980, Ecomat invented a fibreglass mat made from cut textile glass. These fibres, without any chemical addition, are cut and sown together in strips for insulation of washing machines and freezers. Recent innovations in High-Temperature-insulation plates and porous glass are used in chemical, bio-technological and medical indus­try products. With some 850 workers in Germany, China and Poland, the Schuller Compa­ny is still searching for new applications of the High-Tech-fibreglass.

Glass fibres are thin, mostly with a circular profile and are gained from melted glass and manufactured further into threads. A section of a fibre is less than 18 um or 0,00018 mm. They are divided lengthwise comprises the originating technique into both glass filaments and glass stack fibres. Forming it, special pallets of E-glass are used, this alkali-free glass has a high percentage of boric oxide and aluminium and good resistance to water. When fibres must be resistant to acids, S-glass will be used, which is an alka­li-lime-glass with a high borosilicate addition. D-glass is used when di-electric qualities are required –this refers to qualities apparent in an electric field, R-glass is used for high mechanical demands and M-glass for a high elastic standard.

Cutting filaments into fibres obtain staple-fibre-yarns or chopped strands of various lengths.
Glass staple-fibres are primarily fabricated by the glass industry using the spin-blow procedure in which liquid glass runs into spinning nozzles and pneumatic air or gas blows it into mono-threads with a length between 3 mm to 60 mm. This is stretched out by a perfor­ated barrel that sucks and winds up these fibre-threads or yarns. The partially diagonal cross fibres of these threads are not as firm as the spun ones. Immediately after production a substance is added to the fibres that prevents the slippage of glass on glass. For spun glass threads this is called Schliechte, while for glass-staple-fibres Schmälze. These fibres can be spun and twined into glass threads, wadding, membranes and mats.
Additionally, paper sheets, used as very thin separation material for kiln forming techniques, are made out of glass-staple-fibre, while the binder is made of sugar that burns off when heated.

Insulating fibreglass, fibreglass membrane, glass wool or glass wadding are mostly made by an oscillate procedure. In the manufacture of 70 to 80% recycled glass is used while the rest consists of soda, sand and limestone. The liquid glass mass flows from a kiln into a rapidly rotating barrel. In the brim there are tiny holes where the liquid glass is oscillated and fibres are formed. Hot air with the speed of the rotating barrel blow the fibres away and stretch them out into 6 um (0,0006 mm). Because glass coagulates, the fibres break into small pieces, fall onto a moving band that turns them into a felt blanket called wadding. Sprayed with a plastic after drying, the blanket’s pattern becomes firmer in a hardening kiln. This glass wadding blanket or Roving is cut to measure then rolled up or packed as piece goods. It is put upon the market as yarn, joint band, loose wadding, netting blanket or galvanised netting, sewed with glass yarns, as a filling between two paper layers or covered with an aluminium layer on one side. Or, it is in the shape of strips, mats and membranes. Bowls -cylindrical elements- are obtained by shaping glass wadding soaked in a plastic. Pressed parts are obtained by pressing the soaked glass wadding into a plate. Glass wadding has excellent insulation qualities, is water repel­lent, a noise insulator and is fire-proof. Coarse mats of glass fibre are used as air filters and rectifying towers of distillation plants.

End of part I
Read Part II>

Angela van der Burght © 2002 This Side Up!, 2003 Fjoezzz

Thanks to Riekje Jouvenaz-Broekman, former lecturer at the Academy of Visual Arts Maastricht and former member SFBVO Commission Federation BVO and Glossary (Visual Arts Education Foundation Federation) TeHaTex, with whom I wrote most of this article.

Translation: Ingrid Bongers