The invention of glass-blowing did not however, allow the production of large sheets of glass, because the thickness of the centre of the sheets was unpredictable, with the mark of the fracture of the glass stalk. The centre of the glass sheet thus produced, and usable only with difficultly, survived under the (incorrect) designation of the “bottom of the bottle”’. The rest of the glass plate could be cut into small pieces which were, nonetheless, suitable for mounting in open-work windows. Fitted into lead frames, these small glass plates became the foundation of stained glass.

Before the use of diamonds for cutting glass, the normal method was by heat. A red-hot iron was passed over the glass in the intended direction of the cut, which was usually accomplished reasonably successfully. It was then tidied up with pliers.

Because paper was in short supply, the design was drawn in crayon on a table. The design could be modified, which compensated for any errors in the cutting itself. The casting and smoothing of the lead provided additional flexibility as required, as did the grey texture of the lead, as it disappeared into the glass.

The beginning of the fourteenth century saw the appearance of silver stain, a powerful oxide able to gild the glass in depth without affecting its transparency. Used together with glass plates which could be engraved, it made possible the juxtaposition of colours without lead between them. This technique was, of course, used in heraldry, and allowed details to be emphasised.

The Renaissance introduced two other innovations: the use first of diamonds and then of paper to make designs more advanced, and the evolution of the technique of grisaille to give a much more realistic effect.

Lead as a graphic element made a happy return in the peregrinations of the Art Nouveau movement around Europe at the start of the twentieth century. It lent itself also to the contours of the Art Deco movement.

The architecture of the second half of the twentieth century sought to be classical. It only allowed lines and spaces: fussy designs were not welcome. We sometimes have the pleasure of adding the odd baroque touch.

The scale of 1/10 is normally accepted.
The design has to be in complete harmony with the place it is intended to be exhibited, and as close as possible to the requirement, which itself sometimes needs some clarification.
It is important to think about the light, and the degree of transparency required, as well as the specific techniques which will be required. On the other hand, it is important to avoid making the kind of notches in the glass which are difficult to accomplish and make the glass weaker, without rejecting them entirely, since they do make the design more dynamic.

The lead framework should never be intrusive - it should appear to divide the space naturally.
It is important to think about how adjacent pieces of glass will look when they are put in a lead frame.
Finally, samples of the glass should be at hand at all times, to remind you of their colour, their structure and their opacity.

THE DRAWING

The model is reproduced full-size. The lead frame determines how the glass will be cut. Each piece is given a number and details of the glass chosen. If space permits, information about painting is also included.

A careful tracing of the drawing is then made. It will enable the pieces of the puzzle to be reassembled, and, if the drawing is complex, will serve as a guide for reconstituting it.
The drawing can then be cut with special scissors, taking account of the space required for the lead frames.

CUTTING

Once the drawing has been cut into a series of templates, the layout of the lead frames cannot be further modified. The pieces of glass are cut with the aid of a glass-cutter or a diamond, as close as possible to the edge of the template. Some complicated cuts are made in several stages, by approximations. For geometric shapes, a bar gliding along a ruler is used to make sure that repeated elements are absolutely regular. The pieces are then checked, trimmed as required and placed onto the tracing.

PAINTING
The pieces are carefully cleaned, and the sharp edges are rubbed down to avoid damaging the brushes. The line of grisaille, with the addition of gum Arabic diluted in vinegar, is the first thing to be applied with a long fine brush, following the indications on the tracing. The opacity of the line has to be checked regularly in daylight. The lines should be soft, and finish delicately. It is important to execute both upstrokes and down strokes carefully. Practising on complex designs is useful.

The next day, the grisaille in liquid form, diluted with distilled water, can be applied. The grisaille must be finely ground, and applied with a brush of badger’s hair to ensure that it goes where darker tones are required.

When the drying is half completed (or entirely so, depending on the effect sought, lightening takes place with a brush made from the hair of a skunk. When the work is completely dray, straight lines can be made with a needle a sharp stick or an old brush.

A third grisaille, diluted in turpentine, can then be applied, without any need for prior firing, to bind together or strengthen the whole. Enamels or silver stain can be applied drop-by-drop or brushed ob the other side of the glass, and fired at the same time.

The difficulty with painting in this fashion is that the paint does not adhere to the glass, and so each brush-stroke can be diluted by the next one. This difficulty can be avoided to some extent by using a different medium for each application. Similarly, the glass painter proceeds from dark to light tones, separating the details.

MOUNTING
Mounting is carried out on a wooden table, two sides of which are equipped with beadings. Along the length of these beadings, and slightly raised, are two lead frames adapted to the length and width of the piece of glass. Into the angle thus formed, the first piece is placed, secured with a nail in one side. On the other side is fitted a second lead frame which will hold a second piece of glass in place and is fixed by a nail also. When the first nail has been removed, the first piece of lead frame is cut exactly, by crushing its extremity. A second lead frame is then placed, supporting the two pieces. One then proceeds progressively, so that the lead frames cross each other regularly, thus ensuring that the result is solid. By contrast, a single lead frame traversing the entire panel would act as a kind of hinge, making the whole edifice weaker. If the crossing points are obvious enough in the case of a geometric design, they require some forethought if the design is a freer one.

In any case, a beginner would be well-advised to draw a sketch of these crossing points before starting the mounting.

When everything is ready, the lead frames which have been opened to facilitate the mounting are attached to the glass.

At each point where the lead frames cross, solder is applied after the use of an abrasive oil, first on one side of the panel and then the other. Finally, a semi-liquid putty made with linseed oil is firmly applied on both sides, pushed between the glass and the lead to make the whole work stronger and more water-tight. The excess is carefully wiped away.

FITTING
Fitting is done, according to circumstances, in wooden frames such as windows, in metal frames or into the masonry itself. It is a trade quite apart, which, without demanding a mastery of carpentry, ironworking or stone-cutting, nonetheless requires some knowledge of these techniques, as well as great initiative. It should be added that for this trade knowledge of workshop activities, or at least the approach, is essential.

CONCLUSION
This description is not intended as a technical lecture. Rather, the attempt has been to explain the things that seem most important, and, finally, the spirit and the principles which have guided the author’s work.

Parallèlement à son activité de création, l'atelier s'applique depuis 1977 à la restauration et à l'entretien des vitraux.
Si en création notre intention est de trouver des projets en cohérence avec les lieux et les personnes auxquels ils sont destinés, cette démarche débouche souvent sur plusieurs solutions.
En restauration, le but est l'accord parfait des parties restaurées à l'existant.
C'est l'unique solution.
L'intention est d'y parvenir et le métier de s'en approcher.

Restauration et conservation

Dans l'exemple du décor floral ci-dessous, la question se posait de refaire la pièce peinte A en totalité ou uniquement la partie manquante.
Cette seconde possibilité allant dans le sens de la conservation.
Les autres pièces du vitrail étant intactes nous avons choisi de restaurer, de reproduire en totalité la partie brisée pour restituer au vitrail son aspect initial.

Il y a quelques années nous avions restauré de cette façon des vitraux XIXe d'une église paroissiale et j'étais satisfait du résultat, les pièces reproduites étant très proches des originales.
L'architecte affecté aux travaux m'a demandé d'utiliser, à l'avenir, une grisaille de teinte différente afin de pouvoir aisément identifier les parties refaites.

En résumé, la restauration par l'emploi d'une technique contemporaine à son sujet,
assez simple en fait, se qualifie par le degré d'habileté et d'exigence du restaurateur.
L'intuition y trouve sa part. C'est un art et, comme tel inquantifiable.

La conservation consiste à préserver au mieux les parties anciennes, même parcellaires.
Les intervention de métier si elles peuvent être visibles ne doivent pas être irréversibles.
Des technologies nouvelles doivent êtres acquises et leurs applications décrites.
C'est une science. Tout peut être inventorié, quantifié.

Il semble que ces deux approches soient moins antinomiques qu'elles le paraissent, pour autant que nous essayons de résoudre chaque cas au mieux de nos connaissances et capacités.

RESTAURATION D'UN VITRAIL XIXe DECOR FLORAL.
Restitution d'une pièce brisée.

A/ La pièce brisée est extraite

B/ Le verre de support a été retrouvé, c'est un cordelé gris vert.
Le trait est fait d'une grisaille brune proche de l'originale,
diluée au vinaigre avec un peu de gomme arabique.

C/ Après séchage du trait, le lendemain, un jus de grisaille diluée à l'eau est appliqué.
Le jus encore liquide est travaillé au blaireau.
Au séchage, de légers éclaircissements sont exécutés au putois.
Des passages de lumière plus vifs et précis sont faits à l'aide d'un bois aiguisé.

D/ Sur la face extérieure des émaux translucides sont appliqués, à la goutte ou blaireautés
selon l'effet voulu.
Un nettoyage systématique des espaces non peints est fait avant cuisson.

La pièce peut ainsi ne subir qu'une cuisson.
La condition est de réussir d'emblée le jus à l'eau. Y revenir diluerait le trait au vinaigre.
Le verre se peint simultanément sur 2 faces. La face grisaille peut reposer sur la sole du four. La face émaillée est toujours au-dessus.

LE RESEAU DE PLOMB

Le réseau de plomb a une durée de vie de 80 à 120 ans selon l'exposition du panneau ( vent, salinité ….), ses dimensions et les renforts prévus initialement.
La vétusté, chimique comme mécanique se manifeste d'abord par des ruptures au niveau des soudures.

A la dépose, le vitrail peut totalement se désolidariser.
Il convient de le consolider au préalable par l'application de bandes adhésives croisées.

En atelier, le panneau est immergé dans un bain d'eau claire afin d'attendrir les restes de mastic… et de canaliser la poussière. Il est ensuite rincé puis désserti.

Si le dessin des plombs est complexe, naturellement ou du fait d'interventions antérieures, on aura pris soin d'en prendre l'empreinte à l'aide de papier frotté par un chiffon sali.

Les pièces brisées son remplacées ou traitées en conservation. Nous préférons dans ce cas, aux collages, l'emploi de cuivre mince étamé. Ce procédé, plus discret que les plombs de casse ne nécessite pas de gruger les pièces.

Dans les cas d'accidents ou vandalisme, des pièces peuvent être brisées sans que le réseau de plomb soit altéré. Il est alors possible d'intervenir sans déposer le panneau.
Les ailes du plomb sont soulevées précautionneusement avec une lame et la nouvelle pièce est mise en place.
Les ailes sont ensuite rabattues sur un bourrage de mastic gris.

Pour résumer, par son exigence d'accord à l'existant et par les cas particuliers qu'elle oblige à résoudre, la restauration est pour le verrier une école essentielle à l'acquisition de beaucoup de technique et d'un peu d' humilité.