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A design icon in X-ray close-up

by Prof. Dr.-Ing Friederike Deuerler / deuerler@uni-wuppertal.de

Ludwig Mies van der Rohe designed the famous chair for the German pavilion at the Barcelona World Fair in 1929. Since then it has become an icon of modern design. In cooperation with the Federal Institute of Materials Research and Testing (BAM) in Berlin and the Institutes for Welding Engineering (SLV) in Duisburg and Munich the author conducted X-ray analysis of the oldest known examples of the Barcelona chair in order to establish non-destructively how this piece of furniture was made.

The investigation enabled the production period of the chair to be determined, and established parameters for the proximity of any particular example to the original.

Fig 1: Braun prospectus, Frankfurt 1966 (photo: Engel und Norden).

The easy chair displayed in a 1966 Braun prospectus (fig. 1) had awoken my interest, and when I finally found out about its background and manufacturer, I decided to discover the secrets of its construction and production. Ludwig Mies van der Rohe (1886-1969) had built a pavilion for the Barcelona World Fair in 1929 and designed chairs to go with it.

I eagerly followed the reconstruction of the pavilion for Mies’s 100th birthday in 1986; the interior of the main room is shown here (fig. 2) with two of the so-called Barcelona chairs. The frames of these two chairs from Knoll International’s (KI) special series are, however, made of stainless steel and the cushions are of bleached cowhide. The original 1929 chairs had frames of chrome-plated standard construction steel and the cushions were also finished differently.

When I visited Munich’s 1998 Werkstoffwoche (Materials Week), an exhibition on Mies van der Rohe’s Tugendhat Villa was running simultaneously at the Zentralinstitut für Kunstgeschichte. The Tugendhat Villa in Brno (Czech Republic) was built at the same time as the Barcelona pavilion and, like the latter, furnished with specially designed chairs as well as three Barcelona chairs. Built for the entrepreneur couple Fritz and Grete Tugendhat (parents of the German philosopher Ernst Tugendhat), the villa soon became an icon of modern architecture.

Fig 2: Barcelona pavilion, reconstruction 1986 (photo: Hans Deuerler, Barcelona 1986).

The constructional secrets of the Barcelona chair could only be unveiled by elaborate X-ray and computer tomography, and it soon became clear that the attempt to determine the age of an individual chair by materials analysis alone would be about as accurate as reading tea-leaves.

Other criteria had to be applied: measurements of the frame and of the flat steel bars used for its side members, type and layout of the leather straps, material and finish of the cushions, surface finish and quality of the steel used for the frame, construction and curvature of the side members, details of the central node, and construction of the lateral cross pieces and the sides.

To discover what holds the inner core of the Barcelona chair in its original 1929 version together, and how it was manufactured since 1929, it was, therefore, necessary to apply the same sort of non-destructive methods in an engineering context as are normally applied to two-dimensional works of art. This undertaking was greatly aided by links established in 1999 with the German Welding Society (DVS), and a cooperation established in 2004 with BAM, as well as by the welding training offered at the University of Wuppertal’s (BUW) School of Mechanical Engineering.

Fig 3: Strap arrangement of pavilion chairs from pre-war production: Barcelona chairs from the Tugendhat Villa (City of Brno Museum. Photo: Miroslav Ambroz, Brno, April 1, 2011).

Research into the technical and production details of the Barcelona chair began in 2005 in the run-up to the van de Velde Society’s symposium ‘Mies’s Furniture and Interior Design’, scheduled for 2007 in Hagen. Further results of this research, in particular from analysis of materials and production methods, were presented at BUW’s 2009 exhibition ‘The Original from Prototype to Cult Object – Ludwig Mies van der Rohe’s Barcelona Chair’.

The light and elegant 1929 original had a steel frame that seemed to be made in one piece, but a drawing from Mies’s design bureau clearly shows a hairline joint between the side members and horizontal bars. The drawing is dated September 14, 1931, two years after Barcelona, and the original exhibition photos do not reveal whether the steel frames of the chairs there were formed in a single piece or consisted of two side members and three bars. Despite every effort, it has not yet been possible to trace the original chairs with certainty.

However this is not the case with two Barcelona chairs from the Tugendhat Villa. These orginals were rediscovered in Brno in 2010. They differ from each other in the number of leather straps forming the back (fig. 3). The hairline joint between side member and upper bar is visible on the left hand chair.

Fig 4: Pavilion chair cir. 1930 with original strap arrangement (Grassi Museum, Leipzig. Inventory no. 72/35. Photo: Margrit Behrens, Central Institute of Art History, Munich 2007).

Until the rediscovery in Brno, the oldest known chair was that in the Grassi Museum in Leipzig (fig. 4), bearing the inventory date October 27, 1933. Its chrome-plated frame measures 75.5 x 75.0 x 75.3 cm (height x width x depth), and it consists of two side members and three bars.

The side members are made of flat sections of unkilled steel 35 x 15 mm, and each of these members consists of two sharply angled pieces, one facing backward the other forward, welded together with a steel insert at a central joint. The joint itself measures 37 mm across and 34 mm down (fig. 5).

This manner of construction is astonishing because of the stresses it places on the steel strip: extreme stretching at the outside and extreme compression at the inside of the bend. On the other hand it means that only two welding seams have to be finished, one above and one below the joint.

The three horizontal bar assemblages consist of a brass U-section 35 x 14 x 2 mm (length x width x thickness) into which is riveted the flat 10 x 10 mm cross-section steel inlay.

This unit is screwed from the front into a steel connecting piece that is inserted and riveted into the side frame member (fig. 6). The bar is drilled and tapped at regular intervals to take the screws for the strap attachments.

James Johnson Sweeney, art critic, collector, and curator of the Guggenheim Museum, furnished his New York flat in the 1930s with pieces designed by his friend Mies van der Rohe. One of these pieces, a Barcelona chair from Sweeney´s estate, was available for detailed examination.

Fig 5: Central joint of Grassi Museum chair (drawing: Mathias Winkler, Munich 2008; X-ray image: SLV Munich 2007).
Fig 6: Bar / side-frame joint of Grassi Museum chair, Leipzig, 1930-31 (drawing: Mathias Winkler, Munich 2008).

Fig 10: Bauhaus Dessau Foundation chair, office of Military Governor Lucius D. Clay cir. 1954-55. a) side member, b) bar with original leather straps, c) side member with lug for lap joint bearing, hammer-blow number 44, d) central joint (photo: Christoph Becker, Wuppertal 2009).

Its chrome-plated frame measures 75.2 x 75.0 x 75.5 cm and, like the chairs described above, it consists of two side members and three bars. Like them, its side members are made of flat strips of unkilled steel 35 x 15 mm in cross section.

Each of these side members consists of two pieces welded together, but the similarity ends there. In this chair one of the pieces is formed into a flat S, the other into a quarter-circle (radius 75 cm).

Each is notched across half its width at the central joint, which is formed by cross lapping and subsequent four-fold welding and finishing (fig. 7).

The joints on this chair, measuring 34 mm across and 25 mm down, have been executed with great skill and care – in other words at considerable expense.

But from the point of view of the stress imposed on the material this constructional method is preferable.

Fig 7: Central joint of James Johnson Sweeney chair (drawing: Mathias Winkler, Munich 2008; X-ray image: SLV Munich 2007).
Fig 8: Bar / side-frame joint of James Johnson Sweeney chair (drawing: Mathias Winkler, Munich 2008).
Fig 9: Blueprint of Barcelona chair, KI series (drawing no. 239/6, KI., September 13, 1951).

As in the Grassi model, the three bar assemblages consist each of a brass U-section 35 x 14 x 2 mm into which the steel profile is riveted, but this is now rectangular in cross-section: 20 x 10 mm (fig. 8). This unit is again screwed from the front into a steel connecting piece, but this is now brazed into the side frame member. The inlay is again drilled and tapped at regular intervals to take the screws for the leather strap attachments.

The steel frames of these chairs were almost certainly made by the Berlin metalworking company Metallgewerbe Jos. Müller, or its successor, Bamberg Metallwerkstätten, in Berlin-Neukölln. In 1930 this latter company offered the MR 90 chair with chrome-plated metal frame and pigskin cushions for 520 reichsmarks, at the time between two and three months’ wages for a skilled craftsman.

In the interests of rationalization and cost saving, the construction of the Barcelona chair was evidently changed in the short time between 1929 and 1933. The versions sold by KI after the war reveal the same concern with cutting production costs, without seriously compromising Mies’s aesthetic of reduction to the “skin and bones” of constructional essentials. Honesty of construction was his watchword, but the result was on no account to look cheap.

In 1946 Hans G. Knoll, son of a Stuttgart family of cabinet makers and upholsterers, together with his wife Florence (née Schust), founded Knoll Associates Inc. in New York. An interior designer, Florence Knoll had obtained a license from her teacher and mentor Mies van der Rohe to manufacture the Barcelona chair. However, KI did not do this themselves: they had the chairs made by Waldemar Stiegler, a medium-sized metalworking company in Marbach, near Stuttgart. From 1954-1976 the metal frames for the Barcelona chair were produced there as model 250, on the basis of KI drawing no. 239/6, dated September 13, 1951 (fig. 9).

The Bauhaus Foundation in Dessau holds in its archives a chair frame from the office of the Allied Forces’ Military Governor, Lucius D. Clay, that matches the original Knoll drawing (fig. 10). Like the other chairs, it has two side members and three bars. The side members, each made of two 30 x 12 mm chrome-plated steel strips, are again notched and joined by cross lapping as indicated in the drawing. The joint, measuring 30 x 20.6 mm, is considerably reduced and welded with simple fillet welds (fig. 11).

To hold the bars, 85 mm long lugs made of 4 mm gauge flat steel are welded to the side members and the bars are fixed onto these with two screws from the front. The ends of the bars are rabbeted to the thickness of the lugs, resulting in a total bar thickness of 12 mm. In serial production, the lugs and bars are stamped with hammer blow numbers to ensure that the corresponding parts fit together after chromium-plating. (fig. 10).

Fig 11: Bauhaus Dessau Foundation chair, office of Military Governor Lucius D. Clay cir. 1954-55, a) central joint from side, b) central joint from above (X-ray images: Bernhard Redmer, BAM Berlin 2008).

This method of construction indicates the limits of rationalization. The overlap joint between bar and side member affects the stability of the chair, and the lugs on this particular example had been bent and broken in an accident. Because of the inadequacies of frames made to the specifications of drawing 239/6, KI used 14 mm gauge steel strip for later side members, and enlarged the central weld to 40 x 35 mm by inserting metal pieces into the joint. This latter modification is noted in a handwritten revision to the drawing. The reasons for this are aesthetic as well as technical. With the metal inserts the joint looks identical with that of the original Barcelona pavilion chair.

Fig 12: Barcelona chair frame with corner lap joints, a) overall view from above, b) lap joint detail (photos: Christoph Becker, Wuppertal 2009), c) upper bar / right side-member joint from above, d) front strut / right side-member joint from above (photos: Friederike Deuerler, Munich 2007).
Fig 13: Barcelona chair frame with corner lap joints, a) overall view from side (photo: Christoph Becker, Wuppertal 2009), b) central joint (X-ray image: Cord-Christoph Vogt, Schweinfurt 2005).

However, rationalization culminated in constructional measures that really did reach the limits of shoddiness, evident in a version of the frame manufactured between 1955 and 1958 in which the side members were constructed in exactly the same way as before (fig. 13-14), but the bars were connected to the side members by means of simple corner laps reinforced with screws (fig. 12). This involved rabbeting each piece of metal to half its thickness on a milling machine – a simple and inexpensive procedure.

But unless it was executed with great accuracy this type of joint did nothing to improve the stability of the frame, and exact workmanship, being expensive, ran counter to the object of rationalization. Nor would setting the screws diagonally in the joint altogether preclude the collapse of the frame into a parallelogram under high load. Apart from that, the lap joints fail to convince aesthetically.

Fig 14: Central weld of Barcelona chair with corner lap joints 1955, privately owned by Scheufelen Paper Mill (X-ray image: SLV,Duisburg 2010).
Fig 17: Central weld of Barcelona chair by Fa. Stiegler, Marbach, privately owned by Barmenia Insurances Wuppertal (X-ray image: SLV Duisburg 2010).

From about 1958 onward Stiegler developed a version of the frame that broadly satisfied both technical and aesthetic demands and was at the same time inexpensive to manufacture. While the central joint remained initially unchanged, the connection between side members and bars was radically modified. New connecting pieces cut to form a double rabbet and tapped for screws were welded onto the side members (fig. 15), and the bars were rabbeted to match (fig. 16). The two elements were then joined with Allen screws whose heads were sunk flush into the bar. The double rabbet was concealed by the leather straps.

Fig 15: Rabbeted and tapped connecting pieces on side member of Barcelona chair by Fa. Stiegler, Marbach 1970, a) upper connecting piece, b) front connecting piece (photos: Ernst Schauf, Essen 1998), c) X-ray image (SLV Munich 2007).
Fig 16: Struts of Barcelona chair by Fa. Stiegler, Marbach 1970, a) blueprint, b) bar with straps (photo: Ernst Schauf, Essen 1998).

A further modification introduced into the versions produced up to 1976 was to construct the side members of 30 x 14 mm steel strip, as before, but now as an upper and lower unit, curved accordingly (fig. 17). This reduced production costs, because the bend in the steel already provided an upper and lower angle at the point of joining, so only the front and back faces of the joint had to be welded and finished.

Because of the longer radius of the curves, this method made less demands on the material than was the case with the front-and-back Grassi model, and it is in this respect superior. The chairs are still produced today to these specifications, although the measurements of the steel strip for the side members, as well as of the central joint, have been reduced.

This research would not have been possible without the assistance of Edwin Burkhardt, a former employee of Stiegler’s, whom I should like to thank expressly on this occasion: he tirelessly answered all my questions on the Barcelona chair, from 1999 onward.

The research was funded by the German Research Foundation as part of the project ‘A Commented Catalogue of Ludwig Mies van der Rohe’s Furniture and Furniture Designs’ (project no. DE 756/3-1).

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