German Glass Industry Intro 2

German Glass Industry 1 Introduction

{ Spellings (minor) corrected.}



This report contains the information collected in Germany during August and September 1945 by C.I.O.S. Team Group 3, Item 22h in an investigation of technical developments in glass manufacture and research with particular reference to Sheet Window, Plate, Safety and Special glasses, including glass products used for insulation. The information was obtained by the inspection of industrial targets, by enquiry through military channels at both Army Group H.Q. and local Military Government offices and by the interrogation of German Technical personnel.

An attempt was made to cover the maximum number of targets in the British and American zones, the visit being essentially of an exploratory nature. Thorough investigation of all details was thus impossible. More than thirty targets were visited; this total does not include many visits to research workers and departmental heads of firms not directly concerned with building materials who were interviewed by various members of the Team, but mainly by one (J.H.W.), in order to ascertain the works most likely to repay investigation.

Reference to Germany should be read as applying only to the British and American zones and to the present time as being the time of the visit.


The German flat glass industry before the war was closely connected financially with Belgian and French interests and within itself the various producing organisations were in general intricately inter-related. Opportunities for determining the effect of the war on these international and national relationships were not such as to yield reliable information. On the other hand it was apparent that the various groups of Works within an organisation are still behaving in the same way as before the war although intercommunication between scattered related Works is appreciably restricted and only just beginning to open up again.

Deutsche Tafelglas A.G. (DETAG) with head offices in Fürth still control Works at Witten-Krengeldanz and Weiden, Bavaria, but there appears to be uncertainty regarding what is happening in their Works in Russian-occupied Silesia (Kunzendorf), Poland and Czechoslovakia.

Vereinigte Glaswerke, Aachen, still control the four Works at Stolberg, Herzogenrath, Sindorf and Mannheim.

Deutsche Spiegelglas A.G. with Works at Grünenplan and Mitterteich had been working in close co-operation with Schott and Genossen of Jena during the war.

German Glass Industry 2 Introduction

Some relationship appeared to exist between Glas und Spiegelmanufaktur A.G. at Gelsenkirchen-Schalke and Spiegelglaswerke Germania A.G. at Porz-Urbach in that they had the same manager, and between the last named and the adjacent Bheinische Ziehglas A.G. in that the former supplied the latter with producer gas, and perhaps also between there and Rheinische Spiegelglasfabrik at Ratingen.

Bayerische Spiegelglasfabriken Bechmann,Kupfer A.G. with a Head Office in Fürth, has maintained contact with its main Works at Furth-im-Wald but is apparently out of touch with its other Works in Czechoslovakia.

Deutsche Libbey-Owens Gesellschaft für Maschinelle Glasherstellung A.G. (DELOG) with a principal Works at Gelsenkirchen-Rotthausen has retained the partly non-German name.

The glass fibre Works appear to be mainly in two organisations; A.G. der Gerresheimer Glashüttenwerke v. Ferd. Heye control plants at Düsseldorf-Gerresheim, Hamburg-Bergedorf (Oscar Gossler), Ettlingen and Bergisch-Gladbach; Glaswolle Kommanditges. W. Schuller und Co. operate plants at Coburg and in Thuringia and Sudetenland.

It would seem that the German glass industry was allowed to function during the war years generally as previously, apart from some introduction of Party principles into the Works and a pooling of resources to meet the demand for particular products.

It must be remembered, however, that only part of the industry is located in the British and American zones; a very substantial part of it is in Saxony and Silesia in the Russian zone of occupation. No details could be obtained of some special glasses made as war products and it has been concluded that these must have been made in the Russian zone.


(a) General

At the time of the visit only a few isolated Works were producing glass. Although some Works are extensively damaged the stoppage is in general not due to war damage but to shortage of fuel and lack of transportation. As fuel and transportation become available locally, the Military Government authorities are making allocations to window glass makers with the result that two or three additional firms were either about to start or hoping to be starting production in the near future. No factory of course may operate without permission from the Military Government.

German Glass Industry 3 Introduction

No glass Works visited appeared to have been the object of special bombing attacks and damage inside a Works was therefore haphazard. Works, however, in the Aachen area appeared to have been centres in local fighting and had been shelled appreciably. In general damage was mainly superficial, consisting of collapsed buildings rather than of irreparable damage to plant. In some cases the damage has already been made good and the recovered plant restored to normal condition. Extensive maintenance and repair work is being carried out in individual factories in the expectation of an early restart on production. This restarting will be to some extent facilitated by the fact that duplicates of vital plant had been dispersed at an early stage in the war and will now be available more readily than fresh parts can be produced by the steel industry.

In most districts shortage of labour is not expected to retard starting up. On the other hand in areas where there had been fighting works personnel had been conscripted into the Volksturme and the whereabouts of many are still unknown.

(b) Sheet Window Glass

During August only one Works (Witten) was producing glass, the weekly output being then about 600,000 sq. ft. Three other Works (Weiden, Porz-Urbach and Grünenplan) had received fuel allocations and were heating up tank furnaces which before the end of September could be producing weekly a further 750,000 sq. ft. The possible future output of Sheet Window glass is given in Table I; it will be seen that it may exceed six million sq. ft. per week. The seven Works visited in the British and American zones with plant suitable for producing Sheet Window glass have collectively 11 tank furnaces and 43 drawing machines. (A small quantity of Clear Rolled glass, a substitute for Sheet Window glass, was being made at Düsseldorf-Gerresheim, and a small quantity of figured glass at Mannheim-Waldhof).

(c) Plate Glass

No rough cast or polished Plate glass is being produced in Germany at the present time. Only one tank furnace (Stolberg) was seen capable of producing suitable rough cast glass continuously, the bulk of German Plate glass being made by the pot process. It is unlikely that production of Plate glass will be started for some time as Sheet glass is required so urgently and the tanks fitted for producing drawn sheet are sufficiently numerous to absorb the coal as it becomes available. The possible future output of Plate glass will be similar to that before the war, since no new tanks or pot furnaces appear to have been built in recent years.

German Glass Industry 4 Introduction


(Estimated on the basis of 3.0 mm. thickness.)


Location of Works

No. of Tanks

No. of Machines

Type of machines

Width of Sheet



Possible output per week
(Sq. Ft.)





48" - 78"

















59" - 95"










48" - 78"
























Total Weekly Production: 6,300,000 square feet

German Glass Industry 5 Introduction

(d) Glass Fibre

Present output is confined so that from one centrifugal (Schleuder or Haber) unit and one drawing (Gossler) unit at Hamburg and one centrifugal unit at Bergisch-Gladbach, totalling probably 0.5 tons per 24 hour day. The possible future output of Glass Fibre is given in Table II; the figures are estimates only but they indicate that the output may exceed 20,000 tons per annum in the two zones of Western Germany. It was said that the output for the Russian zone had amounted to a further 9,000 tons per annum.


Schleuder Thermal Insulation 2,372
Schuller Thermal Insulation 763
Gossler Thermal Insulation 169
American Type Thermal Insulation 17,420
American Type Continuous Textile Yarn 434
American Type Staple Textile Yarn 135
Total Annual Production 21,293 tons

(e) Pressed and Blown Ware

Only one tank furnace was making products of this type. This is at Essen-Karnap where preserving jars were being made. Three other works visited could also produce pressed and blown ware but no estimate has been attempted of possible outputs because of the wide variety of the products made. Glass bricks, floor tiles and roofing tiles were made during the war at Sindorf, carboys at the Gerresheimer works at Minden and up to one million containers per week at the Gerresheimer works at Düsseldorf; each of these works has plant for making many other glass products.


(a) Research Facilities

Laboratories are possessed by some but not all Works and the work undertaken is limited to simple routine control matters. None of the organisations had central Research Departments although one particularly (DETAG) appeared to have well-trained technical personnel available. The German glass industry contributes to a

German Glass Industry 6 Introduction

common research institution in Berlin run under the direction of Professor Franck. Some work on glass is also done in the Kaiser Wilhelm Institute für Silikat Forschung under Prof. Dr. W. Eitel. A certain amount of development work has been carried out in several works, particularly those of DETAG and Deutsche Spiegelglas.

(b) Fuel

Brown coal, in briquetted form, is the main fuel in use for gas production and the majority of the producers are of a mechanical type, circular and with rotating grates to facilitate ash removal. Several works have gas cleaning plants of a simple type, either just condensation or simple washing. In some cases the tar removed from the dirty gas near the producer is reintroduced into the cleaned gas at the furnace, the object being to make the burn-out of flues unnecessary. One Works (Grünenplan) stated that it disposed of its tar by feeding it into the producer. Washed gas is the general fuel for lehrs.

Some works in the Ruhr (e.g. Witten) are supplied with coke-oven gas and use this in the furnaces; the gas distribution grid is an extensive one.

One organisation (DETAG) has waste-heat boilers in two of its Works and there is also one at Mannheim, but no attempt has been made to adopt crown insulation other than at Gerresheim where a flowing end was insulated.

(c) Raw Materials

Some works, the more modern, have attractive lay-outs for storing and handling batch materials. In one case (at Witten) materials can be transferred pneumatically from incoming wagons, and portable conveyors were seen on several occasions. Again some Mixing Rooms are attractively laid out and commendably clean, but others are the reverse and one measured its raw materials by volume. No recording weighing equipment was seen. One Mixing Room (Grünenplan) built for the production of numerous special glasses has about forty tall narrow hoppers for the various cullets in use. Fully automatic batch monitoring had been adopted at Essen-Karnap.

(d) Furnaces

Novelties in furnace design are mainly connected with the ports and stacks; one tank (Grünenplan) possesses split air passages to bring air both above and below the gas stream entering the port while another has stacks feeding as many as three ports of relatively small size. One tank (Witten) has a suspended crown, flat for the greater part of the span; suspended crowns on the canals to drawing machines were seen on several tanks. Two works (Grünenplan and Mitterteich) have small experimental tanks, both equipped with small Fourcault machines. One or two tanks have horizontal regenerators. The spacing of regenerator packings is in general greater than in

German Glass Industry 7 Introduction

English practice. At Witten the regenerators were cleaned each week. A double crown section was a feature of a tank at Essen-Karnap.

The pot furnaces built to take pots 1-1œ tons capacity all have single large ports at each end.

No electric melting or refining furnaces were seen though one or two pot arches are electrically heated.

Some plants have the furnace control devices very neatly grouped and pyrometric installations are sometimes located in special rooms.

(e) Refractories

Whereas some works have used solely Grossalmerode clay for making their debiteuses, pots and general claywork, others were emphatic in their preference for the French and Belgian clays for their pots. Usually each works has made its own requirements in pots and debiteuses; there appeared to be no case of these coming from other works (except with Sindorf) or outside suppliers, A few works have made their own tank-blocks. There was nothing novel to be seen in the making of debiteuses nor in pot-making. All the pots seen were hand-made; in two works (Stolberg and Herzogenrath) accelerated drying could be carried out in controlled humidity drying chambers.

Most of the tanks contained clay blocks made by Didier-Werke A. G. who appeared also to be the chief suppliers of regenerator bricks. The latter are of the normal fireclay type.

A plant for making electrically fused blocks of Corhart type had been built at Mannheim-Waldhof but had been totally destroyed by bombing before it was put into operation. Several plants used Corhart blocks for tank side walls.

(f) Production Processes

(i) Sheet and Plate Glasses

Two outstanding features of the German flat glass industry are that the bulk of the Sheet glass is made by the Fourcault process while the bulk of the Plate glass is made by intermittent casting from pots or ladling. Rolled Plate is made by the Boudin process in a simple form whilst ornamental, Cathedral and Wired glasses are produced on Chance type machines, or from rolled plate tanks. Both welded and non-welded wire mesh is used.

Filling is done without unusual mechanical assistance except that one tank (Witten) had an elaborately suspended ladle for transferring batch from an overhead hopper to the filling pocket and the larger installations of pot furnaces had filling machines travelling on tracks along the two sides of the furnaces.

German Glass Industry 8 Introduction

Although the bulk of the plates produced intermittently are annealed in moving rail lehrs, there are roller lehrs in two Works (Grünenplan and Mitterteich). Indirect water cooling of the hot end rollers was carried out and lubrication was by pressure.

One Works (Waldsassen) has produced coloured glasses by a flat drawn process and another (Mitterteich) has been carrying out similar experiments with filter glasses, normally produced by hand blowing. Mitterteich includes amongst other products, blown watch and clock glasses, these being bevelled at Grünenplan.

(ii) Glass Fibre

Production processes vary from the early method of drawing down a heated rod to the most modern (pre-war) American high production method. Six fibre works were visited; the processes for which each had plant available are set out in Table III.


Location of Works


No. of units


(1) Centrifugal (wool)

(2) Rotating perforated plates (Continuous fibre)




(1) Owens-Corning (Continuous fibre)

(2) Owens-Corning (staple)




Owens-Corning (wool)



Owens-Corning (Continuous fibre)



Centrifugal (wool)



Drawing from rods (Continuous fibre)


The Herzogenrath plant appeared to have been well run on progressive lines but little, if any, development had taken place since the original installation in the other factories using the Owens-Corning processes. The rod process as used at Coburg was said to be also used in Thuringia but the Thuringian works were not accessible during this visit; very fine fibre (5 to 6 microns in diameter) was claimed to have been made by this Schuller process. This process is, however, dependent on glass rod which is not made in the fibre forming plant but has to be transported from another plant.

German Glass Industry 9 Introduction

A fibre with a high safe working temperature is said to have been produced at Gerresheim from the residue from shale oil distillation retorts.

(iii) Optical Glass.

A process of casting optical glass had been developed at Zwiesel.

(g) Grinding and Polishing

The greater part of the polished Plate glass produced is ground and polished by the Disc process. One works (Herzogenrath) has two continuous machines. Sheet glass (at DELOG) is ground and polished on small rotating tables of fixed position. A great deal of repolishing is done, most Plate Glass Works possessing repolishing sections attached to their grinding and polishing departments.

(h) Auxiliary Processes

(i) Toughening

Only one glass producing Works (Herzogenrath) has a toughening department and this is badly damaged. There are several Works which treat bought Plate glass (e.g. there is one in Aachen) but these were not visited.

(ii) Bending

Many intermittent bending kilns were seen and also a number of kilns built specially for bending searchlight circles.

(iii) Silvering

Both hot and cold processes were in operation but on an intermittent basis.

(iv) Pressing

Two works (Grünenplan and Mitterteich) have large departments for the mass production of pressed lenses.

(i) Warehousing

In one or two Sheet Glass works the Warehouses were the most recently erected buildings, built to take glass by monorail straight from the cutting-off floor. The lay-out generally favoured appeared to be examination along the sides of the rooms, utilising daylight from windows, with packing down the centre.

Since none of the Plate Glass Works were working, no actual routine examination of Plate Glass was seen but the facilities were of the simplest.

Some Warehouses had chutes for taking cullet from the cutters' tables; others had boxes readily handled by two men. In some cases the cullet was weighed.

Packages in most Works were of a simple frame design, wood wool being a common packing material.

German Glass Industry 10 Introduction

(j) Quality of Products

Every opportunity was taken to assess the quality of the products at each Works. In general the Sheet glass was poor as regards lines and distortion and the Plate glass as regards seed and finish. Even glass said to be of older manufacture was below the general British and American standards of quality. Silvered mirrors were not in general copper backed.

(k) General Factory layout, cleanliness, etc.

The German glass Works are widely scattered, being grouped relatively near the various coalfields. In some cases they are in small towns lying out in the country. There is a marked contrast between the few more recently built works (e.g. DETAG and DELOG) and the remainder which appear to have undergone little or no development. On the other hand there is a widespread appreciation of cleanliness and orderliness with regard to tools, surroundings, etc.


Most of the men in the Works visited were middle-aged; they appeared to be steady and conscientious workers. Some Works complained of the dispersal of skilled men to the Army as a result of interference by Nazi overseers with the ordinary management.

Bonus schemes were in force in most works, e.g. for cutters, based on output and also loss, and for producermen, based on furnace output.

Wages paid to workers in the flat glass industry varied from £5-£7 per week (at R.M.12 to the £l), but this was subject to various deductions.


The following targets should be visited preferably when they are working:-

1. Herzogenrath Toughening
2. Stolberg Plate glass tank
3. Grünenplan Watch and clock glass bevelling Special Plate glass compositions and founding details
4. Mitterteich Watch and clock glass blowing
5. Essen-Karnap Tubing, Pressings and Containers

A target as yet unvisited is Saarglass A.K.T. Fennisaar, near Louisenthal-Saar, where there are special recuperators for glass furnaces and burning kiln equipment. Another target worth revisiting is at Minden where Glasfabrik Wittekind is expected to produce carboys by an automatic blowing process.

German Glass Industry 11 Introduction


It must be appreciated that very few of the Works visited were working. Moreover only a short time could be spent in each Works on an exploratory visit such as this, and the guides had to be the personnel available. In some cases these were not always fully aware of the details of the processes normally operated.


It was not possible to find many applications of glass in building owing to the state of devastation prevailing in the cities visited.

No novel uses of glass in building were disclosed in conversation with the various technicians except as regards the application of glass wool for heat and sound insulation. Comparatively large quantities of this material were used in buildings. Glass wool mixed with a water soluble binder has also been used for the rendering of internal wall surfaces. The Finance Ministerium in Munich contains examples of the use of glass fibre blankets for duct insulation.

Relative to thermal insulation, the many miles of pipelines and numbers of steam-heated stills, kettles and the like seen (by J.H.W.) on a visit to the Hessische Lichtenau Powder Plant showed no evidence of surface attack except where definitely corrosive chemicals had been spilled upon the fibre. The protection afforded there was either by their metallic tubes split lengthways and shaped over the fibre coating or by hexagon wire mesh wrapped around it. The use of a facing of coarser fibre to protect an inner finer mass was quite common.

A number of Military Government headquarters were visited and many of these had double-glazed windows. One Works (Sindorf, 12 miles due west of Cologne, Map Reference K51/F25) should be visited by any party of Architects who may be in the vicinity. It produces glass roofing tiles, glass bricks and glass anti-slip floor tiles, and has examples of these in use in its own offices.


A small plant for making this Material was seen at Deutsche Gold u. Silver Anstalt (Degussa) in Frankfurt. The Germans have apparently found a satisfactory method of stabilising a frothed mixture of cement and sand which is poured into moulds and later sawn into blocks. The material is used for partition walls and can be made with a bulk density as low as 400 Kg. per cu. metre.

German Glass Industry 12 Introduction


1. Five "E" Cullet marbles (Herzogenrath)
2. Small piece of glass silk
3. Eight pieces U.V. Absorbing glass (Mitterteich)
4. Silvered plate glass (Fürth)
5. Edge-Forked plate glass (Fürth)
6. Cathedral and ornamental glasses (Sindorf)
7. Strip across flat drawn (Fourcault) Spectacle glass (Mitterteich)
8. Light weight concrete (Degussa)
9. Crucibles made from pure oxide refractory materials (Degussa)
10. Lathe cutting tool made of alumina (Degussa)
11. Continuous fibre (E?) cullet marbles made at Gerresheimer (Ettlingen)