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Summary
Hans-Uli Feldmann
Scribing on coated glass plates:
50 years of technical history at the Federal Office of Topography
In the 19th century, only copper or steel engraving, stone engraving and lithography were used for the production of original maps. With the further development of reprographic technology after 1900, it was possible to draw the originals for maps or, in rare cases, engrave them in an opaque layer on a transparent material such as glass or plastic sheets and processed photographically.
The slow development of the scribing technology was due to various circumstances. Above all, there was a lack of suitable transparent flexible carrier materials, consistent scribe coats, engraving instruments and repro-technical processing options. Alternatives to dimensionally stable but fragile glass were thermally strengthened plastics made of cellulose acetate, vinyl and polyester films. The latter soon became the preferred carrier material due to its toughness, flexibility and dimensional stability. The Swiss Federal Office of Topography also followed the development of this new technology with interest but remained conservatively cautious for various reasons.
On June 21, 1935, the Swiss Federal Council decided to produce a new national map at scales of 1:25,000, 1:50,000 and 1:100,000. However, the Second World War disrupted the development of the national map series considerably. Because of the constantly growing backlog in the planned publication of new sheets, the Federal Council decided in 1949 to commission Professors Eduard Imhof and Alfred Walther with drafting a report to reduce production costs. Their extensive research concluded, among other things, to forego engraving copperplates in the future, and that the map originals should only be drawn – either in separate colors or combined.
Karl Schneider retired as Director of the Federal Office of Topography at the end of 1951. In his place, the Swiss Federal Council appointed Simon Bertschmann as the new director on January 1, 1952. Before that, he was the city surveyor of Zurich, where he was responsible for introducing scribing on coated plastic sheets of Cellon (a cellulose acetate). Bertschmann took note of the report on cost-saving by Imhof and Walther, followed most of the guidelines consistently, but was equally adamant in his own philosophy regarding the replacement of copper engraving. In his opinion, the only option was to engrave in layers on glass plates because of the dimensional accuracy. Straight away the employees had to develop a suitable scribe coat and appropriate engraving equipment. In addition, the precision instrument company Haag-Streit SA in Köniz was called in to advise on and produce engraving instruments and inserts. On July 5, 1953, the employees of the Federal Office of Topography were given the go-ahead for this new technology.
Significant improvements and remarkable cost reductions were realized in a very short time. Despite having reduced the number of employees from 200 to 150, the annual map production increased impressively. Furthermore, a noticeable influence was due to changing the working format, i.e. instead of the previous sheet size of the «Siegfried map» (35 x 24 cm), the new format was that of the «normal sheet» (35 x 48 cm), which was later doubled to the 70 x 48 cm format still in use today. The main players in the technical field were the reproduction specialists Daniel Chervet and Hans Stump as well as the head of cartography Paul Bühler.
In the mid-sixties, the terrain surveys of the first sheets of the national maps were already 10 to 25 years old and were correspondingly outdated. A fundamental update of these sheets was unavoidable. Initially, only the oldest sheets were updated, but from 1968 it was decided to carry out an overall revision in blocks over a six-year cycle. The original red scribe coat on glass plates was also used to update the national map. The cartographer engraved the new map elements right-reading and in the original size, which were then copied together with the existing, still correct map image. Although this updating method was flawless in terms of quality, it involved a relatively large amount of manual retouching and, above all, a great deal of effort in terms of copying.
The development of the etching method in 1969 brought a significant improvement to the updating method, whereby the new map names, height figures and the still correct map image were etched negatively into the scribe coat. The cartographer was then able to add the new elements to the map image on one level without additional, time-consuming image retouching. With the introduction of the etching method, the color of the engraving layer was also changed from aggressive red to a calming green for physiological reasons.
In view of the success that the Federal Office of Topography achieved with the development of the scribing method on glass and having maintained it for almost 50 years, it is astonishing that its origin only exists as a simple document in typewriter font. Although the recipe of the scribe coat solution was sold at least 24 times worldwide to national surveying offices and private cartography companies under license, no attempt was ever made to patent its production.
Ideally, mirror glass plates with a thickness of 4 to 6 mm were suitable for the scribing plates. The resistant scribe coat, which was only a few thousandths of a millimeter thick, consisted of three layers cast on top of each other, each of which ensured certain qualities for the end product. The solutions were poured in a tournette (plate whirler). All three castings were precisely coordinated and even slight deviations from the working instructions resulted in the scribe coat becoming unusable. A list of all chemicals, dosages, aids and forms of application is not provided here for reasons of space.
The advantage of scribing was that it produced a uniform, optimal line definition down to a fineness of 0.05 millimeters and, in contrast to copperplate engraving, it was possible to work right-reading wise. A positive image could be copied directly from the negative lines scribed into the opaque layer for further processing. The scribing tools used were primarily the Haag-Streit scribing ring with ready-made steel burins for single, double or triple lines (e.g. for highways). For the rigid triangular slides, the cartographer ground his own phonographic needles to chisel-shaped points with the specified units of measurement. In addition, steel needles and scrapers were used, which had already been used for copper and stone engraving.
In 1988, the first – and immediately successful – attempt was made at the Federal Office of Topography using computer-aided cartography on a Scitex workstation. However, the hardware and software did not yet meet the requirements of a comprehensive solution. At the end of 2000, computer-aided cartography with desktop workstations and a wide range of software applications marked another change in technology – almost 50 years after the successful beginning of scribing on glass plates.
Translation by Christine Studer
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