Cloisonné stained glass, analysis of materials and conservation constraints

So few news have been preserved as objects made with this procedure and the very process of documentation of these windows has gone through more or less adventurous and ad hoc attempts that have left little or no continuity. In the light of the latest discoveries, it was interesting to write a compilation and computerized text of what we have come to know so far, with analyses that definitively clarify the materials used, finally clearing up the contradiction in the documentation of García-Martín (1,2) and that of the patent described by Strobl (3).

When dealing with cloisonné stained glass, it is necessary to clarify the misunderstanding with another homonymous decorative process, the fired enamel used in jewelry as a pictorial process and cloisonné enamel, which has also had applications on stained glass1. Cloisonné stained glass windows are constructed with tiny glass beads sandwiched between thin strips of brass. There is no baking or welding during the process.

The desire for innovation of the stained glass workshops of the late nineteenth century justifies the fact that the introduction of cloisonné stained glass in Catalonia began. Frederic Vidal i Javelí, owner of the interior decoration company Vidal, sent his son to London to learn a new method of stained glass construction in the workshop that held the patent. This was requested by the company Pfister and Barthels in 1897 who ran as partners the London Cloisonné Glass Company, located in London at 40 Berners Street. So far these are the only known artisans, although the suspicion remains that the number of objects produced is too large in relation to the few documented artisan producers.

In 1898, Frederic Vidal Puig (1882-1950) arrived in London, after only one year in the workshop he had learned enough to produce stained glass in cloisonné technique, so he returned to Barcelona. Soon after, he began teaching his father’s workers the new procedure, but after six months they refused to continue learning, arguing that the technique was too difficult. In 1904 Vidal Puig went to South America where he spent 9 years. He returned, although he never again made cloisonné stained glass windows or engaged in any artistic activity. It is assumed that all the stained glass windows made in this process were made by Vidal Puig’s workshop between 1899 and 1904. García Martín (3,4) and Strobl 5 described the construction process as follows.

It begins with the preparation of a life-size drawing of the object to be built and its placement under a transparent glass of the same size, initially preparing the glass with a solution of gum Arabic. Subsequently, the brass wires will be placed on this glass, duly bent following the contours and adhering them with gum Arabic.

Then the glass particles were progressively added and finally, when they were all arranged, they were glued together by applying hot fish glue. Once the adhesive had dried, the stained glass was covered with another glass pane of lesser thickness, which served only as a cover. The side of this sandwich was closed with a thin bead of putty duly shaped into thin strips 1 cm wide and about 3 mm thick. The side of the whole assembly was finally closed with gummed paper. In some cases, the possibility of closing the stained glass windows with tin-plated copper sheets although only one small object made in this way is known, originally owned by Frederic Vidal Puig himself and used as a color sample to choose the tones during the design of the stained glass.

It should also be added that in some cases translucent objects were not made, but rather appliqués for furniture or tables, so that the base where the particles adhered was not glass but plaster or other materials, and in these cases they did not have any type of cover. Some of these objects that we have been able to observe are in a remarkable state of conservation without the lack of protection having accelerated the deterioration.

After the closure of the only two known companies dedicated to the production of this type of stained glass, the technique was forgotten. During the documentation of the Bertrand i Serra house in Barcelona, the extensive collection of stained glass windows produced with this process was discovered. However, no one was able to recognize or name the technique and the lack of knowledge of the original authors was absolute. The pioneer researcher of the history of cloisonné stained glass windows was Professor Manuel García Martín. The master glassmaker J.M. Bonet was the first to identify the technique and the author of the stained glass windows. Knowing the author of the stained glass Professor Garcia-Martin was able to link Frederic with the London workshop, discovered in the Victoria and Albert Museum a brochure (5,6) on cloisonné stained glass and even contacted descendants of that company that unfortunately could not provide any information. The professor’s work was completed with an exhibition of the stained glass windows of the Bertran and Serra house, which the family gave to the City Council of Barcelona and with the restoration attempts of the cloisonné stained glass windows by the occupational workshop of the Casa Elizalde in Barcelona.

Any subsequent publication (7) to García Martín’s work has provided little new historical information. However, the brilliant publications of this author left a great void in the documentation of the original materials used and although he mentioned the possibility that the binder used was gum Arabic, he did not provide any conclusive analysis. It was not until this author’s research that the Anglo-Saxon world began to make timid attempts to document its heritage in this field, with various objects appearing in England, South Africa and the United States.

With the recent appearance of Professor Strobl ‘s publication in 2007, almost twenty years after Garcia Martin’s publication, news of cloisonné stained glass windows has returned. Strobl was able to find the patent describing the materials and steps taken by The London Cloisonné Glass Company. What was surprising to the community of conservators and historians interested in this type of stained glass was that the binder mentioned by G.M., gum Arabic, was not the only one used in the construction of stained glass. Explicitly mentioning the use of rubber
arabic for fastening the brass strips and fishtail for fastening the balls. G.M.’s documentation had led all conservators who accepted the challenge of restoring a deteriorated stained glass window to use only gum arabic as a binder. This adhesive however yellows very noticeably after a certain time and behaves quite differently from fish glue. This fact makes the restored stained glass windows very detectable in the work carried out by the Elizalde house, the panels are ostensibly yellowed.

After Strobl’s publication, a new restoration was started by the co-author of this text(Jordi Bonet) (9), where work was localized, prioritizing minimal intervention and maintaining the original materials of the stained glass. All previous restorations had worked by disassembling the entire stained glass window to reinstall all the balls and brasses, the pictorial material in this case, to a new glass base.

In the case of this type of stained glass it should be noted that the fragility of the materials used made the stained glass very susceptible to suffer some kind of alteration. For many years it was practically impossible to restore because the procedure was unknown to most glaziers and conservators or it was so laborious to repair that it was economically unfeasible. It is very likely that the stained glass windows with fractures in the back glass were discarded. The number of objects conserved in Catalonia is greater than the number of objects conserved in England. The two adhesives
used are water-soluble, leaks in the panels result in loss of adhesion of the particles, triggering other deteriorations. This is
more likely to occur in countries with more severe rainfall regimes.

The conservation problems of the stained glass windows stem from their own structural constitution, aggravated by the poor performance of the adhesives chosen. Cloisonné stained glass windows were already fragile and weak at the beginning of the century when they left the workshops where they were built. The accidental fracture of the back glass is relatively frequent, since when some of the particles become detached, they are trapped between the two panes and the pictorial layer of adhered glass, favoring the increase of stresses and the breakage of some of the panes.

Structural deterioration, breakage of glass is the last of the stages in the evolution of stained glassThe previous step, the detachment of the elements, glass beads, ground glass or brass strips is given by the weak adhesion to the adhesives and is usually detectable in any of the preserved objects. Although the materials used have been known since ancient times and have had a multitude of applications, it should be noted that none of them has ever been on glass.

The combination of materials is unique and not much can be extracted from the existing literature, neither from the materials and their use in art nor from the classic literature on leaded glass: Theophilo (10), Cennini (11), Pisa (12), Neri (13), Vieil (14).

The two adhesives used in the construction of stained glass, gum arabic and fish glue. They already appear in the classic books on painting materials and methods (15,16,17) and some of the limitations of their use are even discussed. Neither do the articles on chemicals and preservatives provide information that can be extrapolated to this application, since the substrate to be fixed is completely different (18,19,20), in this case the adhesives do not fix pigments, paper or porous wood surfaces. The substrate to be bonded is the brass strips with the base glass on one side and the balls and powder on the other.
glass. Both are very difficult joints as they are surfaces that make it difficult for adhesives to grip. The surface of the glass is surrounded by a thin layer of hydrated silica (21) and the influence this may have on the adhesive in the long term is unknown.

The small 52 x 52 cm treated panel has gone through all the vicissitudes that the lack of knowledge of these objects has caused. Owned by a private collector, it was deposited in the restoration workshop in 1989. It is probably a fragment of one of the leaves of a screen, although its origin is unknown and there is no documentation about its authorship, so we can only assume that it was the work of Frederic Vidal Puig. The soffit was treated in two distinct phases, initially a conservation program was followed following the materials and methods described in the exhibition catalog, which quickly yielded very poor results.

The initial intervention consisted of completely dismantling the panels, and transferring the layer of beads and glass powder to a new glass on which the wires and beads were again adhered. This reconstructive process is very intrusive and the object resulting from the treatment, after the complete manipulation of the object’s material, contains little of the characteristics of the initial one, although the material and the pictorial content are preserved, it clearly loses part of its authenticity and spirit. It is not a process of anastylosis since the base glass is completely new and although the particles are distributed again in the correct position to recompose the initial composition, each particle occupies a new position. These are indistinguishable from each other. This fact is not noticeable to the eye of the observer, but the manipulation of the pictorial material is complete.