Watch glass (clock)
A watch glass is a transparent protection of the dial and the hands of watches in a variety of shapes, sizes and qualities.
Materials
- Right from the start: unhardened mineral glasses (also known as silicate glasses, crystal glasses or glasses made of inorganic glass)
- Since the 1930s: plastic glasses made from plastic sheets
- Since the 1950s: injection-molded plastic glasses made from granulate
- Since the 1970s: hardened mineral glasses
- Since the 1980s: sapphire glasses
Unhardened mineral glass
The first watch glasses were made of glass. When watch glasses were later made from plastics and the trademark Plexiglas was registered for a plastic, the need for clear differentiation arose, especially with watch glasses. In the meantime, the term mineral glass has established itself in the industry, which was recommended by the leading German watch glass manufacturer, Münchmeyer Sternkreuz GmbH & Co. KG , in its multilingual advertising worldwide. Colorless optical glass is used for the watch glasses , which was originally blown into spheres and then broken up into spherical segments. The watch glasses were then cut from the so-called calottes , the edges ground and polished. In the beginning, all watch glasses therefore had a spherical curvature, even if they were e.g. B. were rectangular. Later, the glasses were reheated in small muffle furnaces and pressed into kaolin molds using wooden stamps , so that, for example, larger rounded edges were produced and a variety of shapes with flat surfaces. The edges of these glasses were also ground and polished. Due to the processing, the dimensions spread widely, so the finished glasses were measured and sorted to an accuracy of 1/10 mm. Today optical glass is produced (drawn) in flat sheets.
Plastic glasses made from plastic sheets
At the end of the 1920s and beginning of the 1930s, the North American company Germanow-Simon, Rochester , produced watch glasses made of celluloid , which, with the characteristic “unbreakable”, immediately led to great demand, although the material celluloid is extremely flammable in sunlight in large quantities quickly yellowed and shrunk. Very soon it was replaced by the material cellon , which however had a bluish color of its own and was also not very dimensionally stable. It was not until 1934 that Röhm, Darmstadt, brought the material polymethyl methacrylate to market maturity as Plexiglas that a light-resistant, non-shrinking material was available, which then opened the world market for plastic watch glass. Celluloid , Cellon and also acrylic glass (collective name for numerous commercial brands on the market) were sheet materials that were available in different thicknesses between 0.5 and 1.5 mm, heated and then shaped. Various deformation processes are still in use today.
Injection molded plastic glasses made from granules
In the 1950s, plastic injection molding was ready for the market. The plastic, which is cheaper in the form of granules than the tablets, is pressed into finished steel molds under high pressure and hot, giving it its final shape, from which only the injection point had to be removed. This process has limits for watch glasses because injection-molded plastic parts have asymmetrical manufacturing stresses from the gate. Wrist watch glasses, also known as “small watch glasses” in technical terms, were originally all blasted into the glass edge of the watch case, the bezel , that is, they were inserted with a vaulted tension. The additional manufacturing tension from injection molding will soon cause such blown glasses to crack. For alarm clocks in which the glasses were installed without tension, the injection-molded plastic glass became very popular very quickly. It was only used in wristwatches when installation methods were developed that did not put additional bending stress on the glasses, e.g. B. so-called "armored glasses", with a clamping ring that presses the glass against the bezel.
Hardened mineral glasses
At a very early stage in the history of its development, panes of glass with a thickness of 3 mm or more were stressed by punctual heating and quenching in such a way that they are flexible and crumble into crumbs in the event of destruction. This is called thermal glass hardening. In the 1970s, chemical hardening of glass was invented, in which the desired stress distribution in the glass was created by replacing the smaller ions in the two glass surfaces with larger ones in a salt bath . This made it possible to harden the watch glasses, which were usually 1 mm thick. Since then, these mineral glasses - hardening is taken for granted today - have largely replaced plastic glasses, with the exception of wristwatches in the lower price range. Due to the overall price range of the alarm clocks, alarm clock glasses are still manufactured from plastic using the injection molding process.
Sapphire glasses
The mineral glasses were no longer fragile, but the glass surface remained scratch-sensitive. In contrast to scratches on plastic glasses, the scratches in the mineral glasses were deep grooves that could not be polished out. Aging mineral glasses were scratched until they became opaque. In the meantime, synthetic sapphires were developed, which are produced from alumina at high temperatures, and the processing of these sapphires has been technically solved. The artificial sapphire is initially an elongated pear from which watch glasses are cut out, so to speak, as disks, which then have to be ground and polished. Both the raw material and the processing are expensive. Nevertheless, from a certain class of wristwatches onwards, sapphire glass has largely established itself as the standard.
Paths from the manufacturer to the consumer
Basic equipment
For the watch industry, the watch glasses - and the necessary molds and tools - are made according to the wishes of the watch manufacturer or the case manufacturer. Originally it was counted in dozen (12 pieces) and gros (144 pieces) and packed in rolls. The decimal system now applies and the glasses are often delivered on trays for automatic processing.
Fittings glasses
A watchmaker who replaces a watch glass can now fall back on an enormous range of different sizes and types in different qualities. There are catalogs in many languages for this. The watchmaker buys his needs, which also include many other watch parts, from the watch spare parts wholesaler. The watch spare parts are called watch fittings and the wholesalers are called fittings wholesalers. That is why one also speaks of fittings glasses. The wholesalers themselves maintain large warehouses and, in turn, use the even larger warehouses at the glass manufacturers. The watch glasses for distribution through wholesalers to the watchmaker were originally individually stuck with labels to identify the type and size. The picture shows the labels of the DUF (see below) and some other factories. With the advent of plastic watch glasses, glasses were packaged in individual small bags. Originally, because of the fragility of the glasses, each watch was re-glazed several times in its history. In the meantime, the exchange of glass with the “throw-away watch” in the cheap segment and the sapphire glasses in the better watches has decreased significantly.
History of watch glass production
The beginnings up to the First World War
The first watch glass factories in Europe were built around 1830/1840 in the Vosges in Lorraine . The Chrystallerie de Vallerysthal and Walter Berger & Co in Götzenbrück are well known . From 1860 to 1870 the Verreries de Trois-Fontaines (VTF) took over the market management in Dreibrunnen . These companies obtained the raw glass domes (spherical sections) from Deutsche Spiegelglas AG (DESAG, now Schott AG ) in Grünenplan , Holzminden district . This sheet glass hut manufactured and manufactured optical glass that, in contrast to general window glass, is absolutely colorless. The glass was melted in large clay vats in ports , ten of which were in a large furnace that was originally heated with wood. The ports at the front of the furnace did not get as hot as in the center. The optical quality of the glass was not sufficient for glasses and other optics. The glass for the watch glasses was blown from these ports. For DESAG , whose director at the time was Franz Krippendorff , the sale of glass for watch glasses seemed particularly important. When the largest customer, VTF, threatened to fail because of cheaper competing offers, DESAG founded two watch glass factories in 1906 in cooperation with the leading German furniture wholesalers Flume , Berlin , and Jakob , Leipzig . They originated under the name Jequier & Co in Frammont in the Vosges and in Fleurier in Switzerland. The watch glasses for the two wholesalers involved were sold under their own Elbe brand .
A competition arose both for the watch glasses for the initial equipment of the factories and for the watch glasses for the international spare parts wholesalers, that is for the watchmakers. The prices fell to such an extent that the production of watch glass was threatened. With the involvement of the leading watch company bosses Junghans, Kienzle, Kollmar, Daub and Haller, an agreement was reached in 1912 between the watch glass manufacturers, the watch factories and wholesalers to establish a watch glass label in Strasbourg, the Verreries Unies Strasbourg (VUS). The negotiations were conducted by Rudolf Flume , owner of the Berlin company Flume. A further decline of the watch glass market was prevented and the production of an important article could be maintained. The collaboration was successful until the end of 1918.
From 1918 to 1930
With Germany's capitulation at the end of the First World War , the Treaty of Versailles also expropriated the watch glass factories in Frammont and a share in Fleurier . The French watch glass factories stopped their raw glass purchases from DESAG . Due to inflation and the lack of foreign exchange there were no more watch glasses in Germany. In this situation, the emergency community, consisting of DESAG , the companies Flume , Jacob , Ludwig and Fries, decided in 1919 to found the Deutsche Uhrglasfabrik GmbH (DUF) in Freden , 100 percent of which was taken over by DESAG . The general director of DESAG , Franz Krippendorff, took over the management . This secured DESAG the supply of raw glass and German industry and wholesalers the domestic delivery of watch glasses. Due to the early death of Krippendorff in 1919, the company development came to a standstill. The son Walter Krippendorff had to take over the construction after breaking off his studies in 1920 and was able to carry it out successfully, moving from the founding place Freden to the headquarters of DESAG in Grünenplan. In the early 1920s, 50,000 to 60,000 watch glasses were produced per day.
Fierce competition developed again between the Strasbourg watch glass factory syndicate and DESAG in Grünenplan. Through the mediation of the wholesalers, the DUF was accepted into the syndicate in 1927, but under unfavorable conditions, and it was still fought quietly within the syndicate. This led to the DUF leaving the syndicate in 1937. The DUF has been able to assert itself well on the market, but wristwatch glasses were increasingly made of plastic. In contrast, the market for alarm clock and other large clock glasses grew, especially since plastic injection molding technology did not yet exist. When glasses for alarm clocks were later made of plastic, DUF's production was switched to rear-view mirrors for the car industry. The company became a leader in this segment. The DESAG later became a plant of the company Schott , the DUF closed and transferred production to its main plant. The production of rearview mirrors later abandoned.
Manufactured from plastic
When the first plastic watch glasses came from the United States , DESAG prohibited its daughter, DUF, from starting plastic production. However, the director, Walter Krippendorff, was approved to take action. Together with his war comrade Dipl. Ing. Heinrich Münchmeyer, he founded the company Dipl. Ing. Heinrich in his hometown Verden in 1930/31 . Münchmeyer , today Münchmeyer Sternkreuz GmbH & Co. This company - one of the first German plastics processors - started production from the very beginning, first from celluloid, then from cellon and finally from acrylic glass (Plexiglas).
swell
- German watchmaker newspaper 1920s page 979/980
- DUF documents in family possession Krippendorff
- Personal notes of Walter Krippendorff (1896–1983)
literature
- Johannes Laufer: From glass manufacture to industrial company: Deutsche Spiegelglas AG (1830–1955). Contributions to economic and social history. Ed .: Gömmel, Klug u. Schneider, Vol. 75 in Kom with Franz Steiner Verg. Stuttgart, 1997
Web links
Individual evidence
- ↑ A.-F. Jobin: Classifications of Swiss watch movements and watch fittings. Geneva, around 1938.